RIFT Working Group A. Przygienda, Ed.
Internet-Draft Juniper
Intended status: Standards Track A. Sharma
Expires: 12 January 2022 Comcast
P. Thubert
Cisco
Bruno. Rijsman
Individual
Dmitry. Afanasiev
Yandex
11 July 2021
RIFT: Routing in Fat Trees
draft-ietf-rift-rift-13
Abstract
This document defines a specialized, dynamic routing protocol for
Clos and fat-tree network topologies optimized towards minimization
of control plane state as well as configuration and operational
complexity.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 7
2. A Reader's Digest . . . . . . . . . . . . . . . . . . . . . . 7
3. Reference Frame . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 9
3.2. Topology . . . . . . . . . . . . . . . . . . . . . . . . 15
4. RIFT: Routing in Fat Trees . . . . . . . . . . . . . . . . . 16
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 16
4.1.1. Properties . . . . . . . . . . . . . . . . . . . . . 17
4.1.2. Generalized Topology View . . . . . . . . . . . . . . 17
4.1.3. Fallen Leaf Problem . . . . . . . . . . . . . . . . . 29
4.1.4. Discovering Fallen Leaves . . . . . . . . . . . . . . 31
4.1.5. Addressing the Fallen Leaves Problem . . . . . . . . 32
4.2. Specification . . . . . . . . . . . . . . . . . . . . . . 33
4.2.1. Transport . . . . . . . . . . . . . . . . . . . . . . 34
4.2.2. Link (Neighbor) Discovery (LIE Exchange) . . . . . . 35
4.2.3. Topology Exchange (TIE Exchange) . . . . . . . . . . 49
4.2.4. Reachability Computation . . . . . . . . . . . . . . 74
4.2.5. Automatic Disaggregation on Link & Node Failures . . 76
4.2.6. Attaching Prefixes . . . . . . . . . . . . . . . . . 82
4.2.7. Optional Zero Touch Provisioning (ZTP) . . . . . . . 90
4.3. Further Mechanisms . . . . . . . . . . . . . . . . . . . 102
4.3.1. Route Preferences . . . . . . . . . . . . . . . . . . 102
4.3.2. Overload Bit . . . . . . . . . . . . . . . . . . . . 103
4.3.3. Optimized Route Computation on Leaves . . . . . . . . 103
4.3.4. Mobility . . . . . . . . . . . . . . . . . . . . . . 104
4.3.5. Key/Value Store . . . . . . . . . . . . . . . . . . . 107
4.3.6. Interactions with BFD . . . . . . . . . . . . . . . . 108
4.3.7. Fabric Bandwidth Balancing . . . . . . . . . . . . . 109
4.3.8. Label Binding . . . . . . . . . . . . . . . . . . . . 111
4.3.9. Leaf to Leaf Procedures . . . . . . . . . . . . . . . 111
4.3.10. Address Family and Multi Topology Considerations . . 112
4.3.11. One-Hop Healing of Levels with East-West Links . . . 112
4.4. Security . . . . . . . . . . . . . . . . . . . . . . . . 112
4.4.1. Security Model . . . . . . . . . . . . . . . . . . . 112
4.4.2. Security Mechanisms . . . . . . . . . . . . . . . . . 114
4.4.3. Security Envelope . . . . . . . . . . . . . . . . . . 115
4.4.4. Weak Nonces . . . . . . . . . . . . . . . . . . . . . 118
4.4.5. Lifetime . . . . . . . . . . . . . . . . . . . . . . 120
4.5. Security Association Changes . . . . . . . . . . . . . . 120
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5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 120
5.1. Normal Operation . . . . . . . . . . . . . . . . . . . . 120
5.2. Leaf Link Failure . . . . . . . . . . . . . . . . . . . . 122
5.3. Partitioned Fabric . . . . . . . . . . . . . . . . . . . 123
5.4. Northbound Partitioned Router and Optional East-West
Links . . . . . . . . . . . . . . . . . . . . . . . . . . 125
6. Further Details on Implementation . . . . . . . . . . . . . . 126
6.1. Considerations for Leaf-Only Implementation . . . . . . . 126
6.2. Considerations for Spine Implementation . . . . . . . . . 127
7. Security Considerations . . . . . . . . . . . . . . . . . . . 127
7.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 127
7.2. Malformed Packets . . . . . . . . . . . . . . . . . . . . 128
7.3. ZTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
7.4. Lifetime . . . . . . . . . . . . . . . . . . . . . . . . 128
7.5. Packet Number . . . . . . . . . . . . . . . . . . . . . . 128
7.6. Outer Fingerprint Attacks . . . . . . . . . . . . . . . . 129
7.7. TIE Origin Fingerprint DoS Attacks . . . . . . . . . . . 129
7.8. Host Implementations . . . . . . . . . . . . . . . . . . 129
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 130
8.1. Requested Multicast and Port Numbers . . . . . . . . . . 130
8.2. Requested Registries with Suggested Values . . . . . . . 130
8.2.1. Registry RIFT_v5/common/AddressFamilyType" . . . . . 131
8.2.2. Registry RIFT_v5/common/HierarchyIndications" . . . . 131
8.2.3. Registry RIFT_v5/common/IEEE802_1ASTimeStampType" . . 131
8.2.4. Registry RIFT_v5/common/IPAddressType" . . . . . . . 132
8.2.5. Registry RIFT_v5/common/IPPrefixType" . . . . . . . . 132
8.2.6. Registry RIFT_v5/common/IPv4PrefixType" . . . . . . . 133
8.2.7. Registry RIFT_v5/common/IPv6PrefixType" . . . . . . . 133
8.2.8. Registry RIFT_v5/common/PrefixSequenceType" . . . . . 133
8.2.9. Registry RIFT_v5/common/RouteType" . . . . . . . . . 134
8.2.10. Registry RIFT_v5/common/TIETypeType" . . . . . . . . 135
8.2.11. Registry RIFT_v5/common/TieDirectionType" . . . . . . 135
8.2.12. Registry RIFT_v5/encoding/Community" . . . . . . . . 136
8.2.13. Registry RIFT_v5/encoding/KeyValueTIEElement" . . . . 136
8.2.14. Registry RIFT_v5/encoding/LIEPacket" . . . . . . . . 137
8.2.15. Registry RIFT_v5/encoding/LinkCapabilities" . . . . . 139
8.2.16. Registry RIFT_v5/encoding/LinkIDPair" . . . . . . . . 139
8.2.17. Registry RIFT_v5/encoding/Neighbor" . . . . . . . . . 140
8.2.18. Registry RIFT_v5/encoding/NodeCapabilities" . . . . . 141
8.2.19. Registry RIFT_v5/encoding/NodeFlags" . . . . . . . . 141
8.2.20. Registry RIFT_v5/encoding/NodeNeighborsTIEElement" . 142
8.2.21. Registry RIFT_v5/encoding/NodeTIEElement" . . . . . . 142
8.2.22. Registry RIFT_v5/encoding/PacketContent" . . . . . . 143
8.2.23. Registry RIFT_v5/encoding/PacketHeader" . . . . . . . 144
8.2.24. Registry RIFT_v5/encoding/PrefixAttributes" . . . . . 144
8.2.25. Registry RIFT_v5/encoding/PrefixTIEElement" . . . . . 145
8.2.26. Registry RIFT_v5/encoding/ProtocolPacket" . . . . . . 145
8.2.27. Registry RIFT_v5/encoding/TIDEPacket" . . . . . . . . 146
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8.2.28. Registry RIFT_v5/encoding/TIEElement" . . . . . . . . 146
8.2.29. Registry RIFT_v5/encoding/TIEHeader" . . . . . . . . 147
8.2.30. Registry RIFT_v5/encoding/TIEHeaderWithLifeTime" . . 147
8.2.31. Registry RIFT_v5/encoding/TIEID" . . . . . . . . . . 148
8.2.32. Registry RIFT_v5/encoding/TIEPacket" . . . . . . . . 148
8.2.33. Registry RIFT_v5/encoding/TIREPacket" . . . . . . . . 149
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 149
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 150
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 150
11.1. Normative References . . . . . . . . . . . . . . . . . . 150
11.2. Informative References . . . . . . . . . . . . . . . . . 152
Appendix A. Sequence Number Binary Arithmetic . . . . . . . . . 154
Appendix B. Information Elements Schema . . . . . . . . . . . . 155
B.1. Backwards-Compatible Extension of Schema . . . . . . . . 156
B.2. common.thrift . . . . . . . . . . . . . . . . . . . . . . 157
B.3. encoding.thrift . . . . . . . . . . . . . . . . . . . . . 162
Appendix C. Constants . . . . . . . . . . . . . . . . . . . . . 169
C.1. Configurable Protocol Constants . . . . . . . . . . . . . 169
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 171
1. Introduction
Clos [CLOS] topologies (called commonly a fat tree/network in modern
IP fabric considerations [VAHDAT08] as homonym to the original
definition of the term [FATTREE]) have gained prominence in today's
networking, primarily as result of the paradigm shift towards a
centralized data-center based architecture that is poised to deliver
a majority of computation and storage services in the future. Many
builders of such IP fabrics desire a protocol that auto-configures
itself and deals with failures and mis-configurations with a minimum
of human intervention. Such a solution would allow local IP fabric
bandwidth to be consumed in a 'standard component' fashion, i.e.
provision it much faster and operate it at much lower costs than
today, much like compute or storage is consumed already.
In looking at the problem through the lens of such IP fabric
requirements, RIFT addresses those challenges not through an
incremental modification of either a link-state (distributed
computation) or distance-vector (diffused computation) techniques but
rather a mixture of both, colloquially best described as "link-state
towards the spines" and "distance vector towards the leaves". In
other words, "bottom" levels are flooding their link-state
information in the "northern" direction while each node generates
under normal conditions a "default route" and floods it in the
"southern" direction. This type of protocol allows naturally for
highly desirable aggregation. Alas, such aggregation could blackhole
traffic in cases of misconfiguration or while failures are being
resolved or even cause partial network partitioning and this has to
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be addressed by some adequate mechanism. The approach RIFT takes is
described in Section 4.2.5 and is basically based on automatic,
sufficient disaggregation of prefixes in case of link and node
failures.
The protocol does further provide
* optional fully automated construction of fat-tree topologies based
on detection of links without any configuration (Section 4.2.7)
while allowing for traditional configuration and arbitrary mix of
both types of nodes as well,
* minimum amount of routing state held at each level,
* automatic pruning and load balancing of topology flooding
exchanges over a sufficient subset of links which resolves the
traditional problem of link-state protocol struggling with densely
meshed graphs due to high volume of flooding traffic
(Section 4.2.3.9),
* automatic aggregation (Section 4.2.3.8) and consequently automatic
disaggregation (Section 4.2.5) of prefixes on link and node
failures to prevent black-holing and suboptimal routing,
* loop-free non-ECMP forwarding due to its inherent valley-free
nature,
* fast mobility (Section 4.3.4),
* re-balancing of traffic towards the spines based on bandwidth
available (Section 4.3.7.1) and finally
* mechanisms to synchronize a limited key-value data-store
(Section 4.3.5.1) that can be used after protocol convergence to
e.g. bootstrap higher levels of functionality on nodes.
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Figure 1 presents as first example of operation a simplified,
conceptual view of the resulting information and routes on a RIFT
fabric. The top of the fabric is holding in its link-state database
the information about the nodes below it and the routes to them
whereas the notation A/32 is used to indicate a loopback route to
node A and 0/0 is the usual notation for a default route. First row
of information represents the nodes for which full topology
information is available. The second row of the database table
indicates that partial information of other nodes in the same level
is available as well. Such information will be necessary to perform
certain algorithms necessary for correct protocol operation. When
"bottom" of the fabric is considered, or in other words the leaves,
the topology is basically empty and, under normal conditions, the
leaves hold a load balanced default route to the next level.
The balance of this document fills in the protocol specification
details.
[A,B,C,D]
[E]
+-----+ +-----+
| E | | F | A/32 @ [C,D]
+-+-+-+ +-+-+-+ B/32 @ [C,D]
| | | | C/32 @ C
| | +-----+ | D/32 @ D
| | | |
| +------+ |
| | | |
[A,B] +-+---+ | | +---+-+ [A,B]
[D] | C +--+ +-+ D | [C]
+-+-+-+ +-+-+-+
0/0 @ [E,F] | | | | 0/0 @ [E,F]
A/32 @ A | | +-----+ | A/32 @ A
B/32 @ B | | | | B/32 @ B
| +------+ |
| | | |
+-+---+ | | +---+-+
| A +--+ +-+ B |
0/0 @ [C,D] +-----+ +-----+ 0/0 @ [C,D]
Figure 1: RIFT Information Distribution
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1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they
appear in all capitals, as shown here.
2. A Reader's Digest
This section should serve as an initial guided tour through the
document in order to convey the necessary information for any reader,
depending on their level of interest. The glossary section
(Section 3.1) should be used as a supporting reference as the
document is read.
The indications to direction (i.e. "top", "bottom", etc.) referenced
in the Section 1 are of paramount importance. RIFT requires a
topology with a sense top and bottom in order to properly achieve a
sorted topology. Clos, Fat-Tree, and other similarly structured
networks are conducive to such requirements. RIFT does allow for
further relaxation of these constraints, they will be mentioned later
in this section.
Operators and implementors alike must understand if multi-plane IP
fabrics are of interest or not. Section 3.2 illustrates an example
of both single-plane in Figure 2 and multi-plane fabric in Figure 3.
Multi-plane fabrics require understanding of additional RIFT concepts
(e.g. negative disaggregation in Section 4.2.5.2) that are otherwise
unnecessary in context of strictly single-plane fabrics. Overview
(Section 4.1) and Section 4.1.2 aim to provide enough context to
determine if multi-plane fabrics are of interest to the reader. The
Fallen Leaf part (Section 4.1.3), and additionally Section 4.1.4 and
Section 4.1.5 describe further considerations that are specific to
multi-plane fabrics.
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The fundamental protocol concepts are described starting in the
specification part (Section 4.2), but some sub-sections are not quite
as relevant unless dealing with implementation of the protocol. The
protocol transport (Section 4.2.1) is of particular importance for
two reasons. First, it introduces RIFT's packet formats in the form
of a normative Thrift model given in Appendix B.3. Second, the
Thrift model component is a prelude to understanding the RIFT's
inherent security features as defined in the security segment
(Section 7). The normative schema defining the Thrift model can be
found in both Appendix B.2 and Appendix B.3. Furthermore, while a
detailed understanding of Thrift and the models are not required
unless implementing RIFT, they may provide additional useful
information for other readers.
If implementing RIFT to support multi-plane topologies Section 4.2
should be reviewed in its entirety in conjunction with previously
mentioned Thrift schemas. Sections not relevant to single-plane
implementations will be noted later in the section. Special
attention should be paid to the LIE definitions part (Section 4.2.2)
as it not only outlines basic neighbor discovery and adjacency
formation, but also provides necessary context for RIFT's ZTP
(Section 4.2.7) and mis-cabling detection capabilities that allow it
to automatically detect and build the underlay topology with a
negligible configuration. These specific capabilities are detailed
in Section 4.2.7.
For other readers, the following sections provide a more detailed
understanding of the fundamental properties and highlight some
additional benefits of RIFT such as link state packet formats, highly
efficient flooding, synchronization, loop-free path computation and
link-state database maintenance - Section 4.2.3, Section 4.2.3.2,
Section 4.2.3.3, Section 4.2.3.4, Section 4.2.3.6, Section 4.2.3.7,
Section 4.2.3.8, Section 4.2.4, Section 4.2.4.1, Section 4.2.4.2,
Section 4.2.4.3, Section 4.2.4.4. RIFT's unique ability to perform
weighted unequal-cost load balancing of traffic across all available
links is outlined in Section 4.3.7 with an accompanying example.
Section 4.2.5 is the place where the single-plane vs. multi-plane
requirement is explained in more detail. For those interested in
single-plane fabrics, only Section 4.2.5.1 is required. For the
multi-plane interested reader Section 4.2.5.2, Section 4.2.5.2.1,
Section 4.2.5.2.2, and Section 4.2.5.2.3 are also mandatory.
Section 4.2.6 is especially important for any multi-plane interested
reader as it outlines how the RIB and FIB are built via the
disaggregation mechanisms, but also illustrates how they prevent
defective routing decisions (e.g. black holes) in both single or
multi-plane topologies.
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Section 5 contains a set of comprehensive examples that continue to
highlight just how efficiently RIFT handles failures by containing
impact to only the required set of nodes. It should also help cement
some of RIFT's core concepts in the reader's mind.
Last, but not least, RIFT has other optional capabilities. One
example is the key-value data-store, which enables RIFT to advertise
data post-convergence in order to bootstrap higher levels of
functionality (e.g. operational telemetry). Those are covered in
Section 4.3 and Section 6.
More information related to RIFT can be found in the "RIFT
Applicability" [APPLICABILITY] document, which discusses alternate
topologies upon which RIFT may be deployed, use cases where it is
applicable, and presents operational considerations that complement
this document.
3. Reference Frame
3.1. Terminology
This section presents the terminology used in this document.
Crossbar:
Physical arrangement of ports in a switching matrix without
implying any further scheduling or buffering disciplines.
Clos/Fat Tree:
This document uses the terms Clos and Fat Tree interchangeably
whereas it always refers to a folded spine-and-leaf topology with
possibly multiple Points of Delivery (PoDs) and one or multiple
Top of Fabric (ToF) planes. Several modifications such as leaf-
2-leaf shortcuts and multiple level shortcuts are possible and
described further in the document.
Directed Acyclic Graph (DAG):
A finite directed graph with no directed cycles (loops). If links
in a Clos are considered as either being all directed towards the
top or vice versa, each of such two graphs is a DAG.
Folded Spine-and-Leaf:
In case the Clos fabric input and output stages are analogous, the
fabric can be "folded" to build a "superspine" or top which is
called Top of Fabric (ToF) in this document.
Level:
Clos and Fat Tree networks are topologically partially ordered
graphs and 'level' denotes the set of nodes at the same height in
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such a network, where the bottom level (leaf) is the level with
lowest value. A node has links to nodes one level down and/or one
level up. Under some circumstances, a node may have links to
nodes at the same level and a leaf may have links to nodes
multiple levels higher. RIFT counts levels from top-of-fabric
(ToF) numerically down. Level 0 always implies a leaf in RIFT but
a leaf does not have to be level 0. Level in RIFT can be
configured or automatically derive its level via ZTP as explained
in Section 4.2.7. As final footnote: Clos terminology uses often
the concept of "stage" but due to the folded nature of the Fat
Tree it is not used from this point on to prevent
misunderstandings.
Superspine, Aggregation/Spine and Edge/Leaf Switches:"
Traditional level names in 5-stages folded Clos for Level 2, 1 and
0 respectively (counting up from the bottom). We normalize this
language to talk about top-of-fabric (ToF), top-of-pod (ToP) and
leaves.
Zero Touch Provisioning (ZTP):
Optional RIFT mechanism which allows to derive node levels
automatically based on minimum configuration. Such a mininum
configuration consists solely of ToFs being configured as such.
Point of Delivery (PoD):
A self-contained vertical slice or subset of a Clos or Fat Tree
network containing normally only level 0 and level 1 nodes. A
node in a PoD communicates with nodes in other PoDs via the Top-
of-Fabric. PoDs are numbered to distinguish them and PoD value 0
(defined later in the encoding schema as `common.default_pod`) is
used to denote "undefined" or "any" PoD.
Top of PoD (ToP):
The set of nodes that provide intra-PoD communication and have
northbound adjacencies outside of the PoD, i.e. are at the "top"
of the PoD.
Top of Fabric (ToF):
The set of nodes that provide inter-PoD communication and have no
northbound adjacencies, i.e. are at the "very top" of the fabric.
ToF nodes do not belong to any PoD and are assigned
`common.default_pod` PoD value to indicate the equivalent of "any"
PoD.
Spine:
Any nodes north of leaves and south of top-of-fabric nodes.
Multiple layers of spines in a PoD are possible.
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Leaf:
A node without southbound adjacencies. As mentioned before, Level
0 implies a leaf in RIFT but a leaf does not have to be level 0.
Top-of-fabric Plane or Partition:
In large fabrics top-of-fabric switches may not have enough ports
to aggregate all switches south of them and with that, the ToF is
'split' into multiple independent planes. Section 4.1.2 explains
the concept in more detail. A plane is subset of ToF nodes that
see each other through south reflection or E-W links.
Radix:
A radix of a switch is number of switching ports it provides.
It's sometimes called fanout as well.
North Radix:
Ports cabled northbound to higher level nodes.
South Radix:
Ports cabled southbound to lower level nodes.
South/Southbound and North/Northbound (Direction):
When describing protocol elements and procedures, in different
situations the directionality of the compass is used. I.e.,
'lower', 'south' or 'southbound' mean moving towards the bottom of
the Clos or Fat Tree network and 'higher', 'north' and
'northbound' mean moving towards the top of the Clos or Fat Tree
network.
Northbound Link:
A link to a node one level up or in other words, one level further
north.
Southbound Link:
A link to a node one level down or in other words, one level
further south.
East-West (E-W) Link:
A link between two nodes at the same level. East-West links are
normally not part of Clos or "fat-tree" topologies.
Leaf shortcuts (L2L):
East-West links at leaf level will need to be differentiated from
East-West links at other levels.
Routing on the host (RotH):
Modern data center architecture variant where servers/leaves are
multi-homed and consecutively participate in routing.
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Northbound representation:
Subset of topology information flooded towards higher levels of
the fabric.
Southbound representation:
Subset of topology information sent towards a lower level.
South Reflection:
Often abbreviated just as "reflection", it defines a mechanism
where South Node TIEs are "reflected" from the level south back up
north to allow nodes in the same level without E-W links to "see"
each other's node Topology Information Elements (TIEs).
TIE:
This is an acronym for a "Topology Information Element". TIEs are
exchanged between RIFT nodes to describe parts of a network such
as links and address prefixes. A TIE has always a direction and a
type. North TIEs (sometimes abbreviated as N-TIEs) are used when
dealing with TIEs in the northbound representation and South-TIEs
(sometimes abbreviated as S-TIEs) for the southbound equivalent.
TIEs have different types such as node and prefix TIEs.
Node TIE:
This stands as acronym for a "Node Topology Information Element",
which contains all adjacencies the node discovered and information
about the node itself. Node TIE should NOT be confused with a
North TIE since "node" defines the type of TIE rather than its
direction. Consequently North Node TIEs and South Node TIEs
exist.
Prefix TIE:
This is an acronym for a "Prefix Topology Information Element" and
it contains all prefixes directly attached to this node in case of
a North TIE and in case of South TIE the necessary default routes
the node advertises southbound.
Key Value (KV) TIE:
A TIE that is carrying a set of key value pairs [DYNAMO]. It can
be used to distribute non topology related information within the
protocol.
TIDE:
Topology Information Description Element carrying descriptors of
the TIEs stored in the node.
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TIRE:
Topology Information Request Element carrying set of TIDE
descriptors. It can both confirm received and request missing
TIEs.
Disaggregation:
Process in which a node decides to advertise more specific
prefixes Southwards, either positively to attract the
corresponding traffic, or negatively to repel it. Disaggregation
is performed to prevent black-holing and suboptimal routing to the
more specific prefixes.
LIE:
This is an acronym for a "Link Information Element" exchanged on
all the system's links running RIFT to form ThreeWay adjacencies
and carry information used to perform Zero Touch Provisioning
(ZTP) of levels.
Flood Repeater (FR):
A node can designate one or more northbound neighbor nodes to be
flood repeaters. The flood repeaters are responsible for flooding
northbound TIEs further north. The document sometimes calls them
flood leaders as well.
Bandwidth Adjusted Distance (BAD):
Each RIFT node can calculate the amount of northbound bandwidth
available towards a node compared to other nodes at the same level
and can modify the route distance accordingly to allow for the
lower level to adjust their load balancing towards spines.
Overloaded:
Applies to a node advertising the `overload` attribute as set.
Overload attribute is carried in the `NodeFlags` object of the
encoding schema.
Interface:
A layer 3 entity over which RIFT control packets are exchanged.
ThreeWay Adjacency:
RIFT tries to form a unique adjacency over an interface and
exchange local configuration and necessary ZTP information. An
adjacency is only advertised in node TIEs and used for
computations after it achieved ThreeWay state, i.e. both routers
reflected each other in LIEs including relevant security
information. Nevertheless, LIEs before ThreeWay state is reached
may carry ZTP related information already.
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Bi-directional Adjacency:
Bidirectional adjacency is an adjacency where nodes of both sides
of the adjacency advertised it in the node TIEs with the correct
levels and system IDs. Bi-directionality is used to check in
different algorithms whether the link should be included.
Neighbor:
Once a ThreeWay adjacency has been formed a neighborship
relationship contains the neighbor's properties. Multiple
adjacencies can be formed to a remote node via parallel interfaces
but such adjacencies are *not* sharing a neighbor structure.
Saying "neighbor" is thus equivalent to saying "a ThreeWay
adjacency".
Cost:
The term signifies the weighted distance between two neighbors.
Distance:
Sum of costs (bound by infinite distance) between two nodes.
Shortest-Path First (SPF):
A well-known graph algorithm attributed to Dijkstra [DIJKSTRA]
that establishes a tree of shortest paths from a source to
destinations on the graph. SPF acronym is used due to its
familiarity as general term for the node reachability calculations
RIFT can employ to ultimately calculate routes of which Dijkstra
algorithm is a possible one.
North SPF (N-SPF):
A reachability calculation that is progressing northbound, as
example SPF that is using South Node TIEs only. Normally it
progresses a single hop only and installs default routes.
South SPF (S-SPF):
A reachability calculation that is progressing southbound, as
example SPF that is using North Node TIEs only.
Security Envelope:
RIFT packets are flooded within an authenticated security envelope
that allows to protect the integrity of information a node
accepts.
System ID:
Each RIFT node identifies itself by a valid, network wide unique
number when trying to build adjacencies or describing its
topology. RIFT System IDs can be auto-derived or configured.
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Additionally, when the specification refers to elements of packet
encoding or constants provided in the Appendix B grave accents are
used, e.g. `invalid_distance`. Same convention is used when
referring to finite state machine states or events outside the
context of the machine itself, e.g. `OneWay`.
3.2. Topology
^ N +--------+ +--------+
Level 2 | |ToF 21| |ToF 22|
W <-*-> E ++-+--+-++ ++-+--+-++
| | | | | | | | |
S v P111/2 P121/2 | | | |
^ ^ ^ ^ | | | |
| | | | | | | |
+--------------+ | +-----------+ | | | +---------------+
| | | | | | | |
South +-----------------------------+ | | ^
| | | | | | | All TIEs
0/0 0/0 0/0 +-----------------------------+ |
v v v | | | | |
| | +-+ +<-0/0----------+ | |
| | | | | | | |
+-+----++ optional +-+----++ ++----+-+ ++-----++
Level 1 | | E/W link | | | | | |
|Spin111+----------+Spin112| |Spin121| |Spin122|
+-+---+-+ ++----+-+ +-+---+-+ ++---+--+
| | | South | | | |
| +---0/0--->-----+ 0/0 | +----------------+ |
0/0 | | | | | | |
| +---<-0/0-----+ | v | +--------------+ | |
v | | | | | | |
+-+---+-+ +--+--+-+ +-+---+-+ +---+-+-+
Level 0 | | (L2L) | | | | | |
|Leaf111+~~~~~~~~~~+Leaf112| |Leaf121| |Leaf122|
+-+-----+ +-+---+-+ +--+--+-+ +-+-----+
+ + \ / + +
Prefix111 Prefix112 \ / Prefix121 Prefix122
multi-homed
Prefix
+---------- PoD 1 ---------+ +---------- PoD 2 ---------+
Figure 2: A Three Level Spine-and-Leaf Topology
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+--------+ +--------+ +--------+ +--------+
|ToF A1| |ToF B1| |ToF B2| |ToF A2|
++-+-----+ ++-+-----+ ++-+-----+ ++-+-----+
| | | | | | | |
| | | | | +---------------+
| | | | | | | |
| | | +-------------------------+ |
| | | | | | | |
| +-----------------------+ | | | |
| | | | | | | |
| | +---------+ | +---------+ | |
| | | | | | | |
| +---------------------------------+ | |
| | | | | | | |
++-+-----+ ++-+-----+ +--+-+---+ +----+-+-+
|Spine111| |Spine112| |Spine121| |Spine122|
+-+---+--+ ++----+--+ +-+---+--+ ++---+---+
| | | | | | | |
| +--------+ | | +--------+ |
| | | | | | | |
| -------+ | | | +------+ | |
| | | | | | | |
+-+---+-+ +--+--+-+ +-+---+-+ +---+-+-+
|Leaf111| |Leaf112| |Leaf121| |Leaf122|
+-------+ +-------+ +-------+ +-------+
Figure 3: Topology with Multiple Planes
Topology in Figure 2 is refered to in all further considerations.
This figure depicts a generic "single plane fat-tree" and the
concepts explained using three levels apply by induction to further
levels and higher degrees of connectivity. Further, this document
will deal also with designs that provide only sparser connectivity
and "partitioned spines" as shown in Figure 3 and explained further
in Section 4.1.2.
4. RIFT: Routing in Fat Trees
Remainder of this documents presents the detailed specification of a
protocol optimized for Routing in Fat Trees (RIFT) that in most
abstract terms has many properties of a modified link-state protocol
when distributing information northbound and a distance vector
protocol when distributing information southbound. While this is an
unusual combination, it does quite naturally exhibit the desirable
properties desired.
4.1. Overview
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4.1.1. Properties
The most singular property of RIFT is that it floods link-state
information northbound only so that each level obtains the full
topology of levels south of it. Link-State information is, with some
exceptions, never flooded East-West or back South again. Exceptions
like south reflection is explained in detail in Section 4.2.5.1 and
east-west flooding at ToF level in multi-plane fabrics is outlined in
Section 4.1.2. In the southbound direction, the necessary routing
information, normally just the default route, propagates one hop
south and is 're-advertised' by nodes at next lower level. However,
RIFT uses flooding in the southern direction as well to avoid the
overhead of building an update per adjacency. For the moment
describing the East-West direction is left out.
Those information flow constraints create not only an anisotropic
protocol (i.e. the information is not distributed "evenly" or
"clumped" but summarized along the N-S gradient) but also a "smooth"
information propagation where nodes do not receive the same
information from multiple directions at the same time. Normally,
accepting the same reachability on any link, without understanding
its topological significance, forces tie-breaking on some kind of
distance metric. And such tie-breaking leads ultimately in hop-by-
hop forwarding to shortest paths only. In contrast to that, RIFT,
under normal conditions, does not need to tie-break the same
reachability information from multiple directions. Its computation
principles (south forwarding direction is always preferred) leads to
valley-free [VFR] forwarding behavior. And since valley free routing
is loop-free, it can use all feasible paths which is another highly
desirable property if available bandwidth should be utilized to the
maximum extent possible.
To account for the "northern" and the "southern" information split
the link state database is partitioned accordingly into "north
representation" and "south representation" TIEs. In simplest terms
the North TIEs contain a link state topology description of lower
levels and and South TIEs carry simply node description of the level
above and default routes pointing north. This oversimplified view
will be refined gradually in the following sections while introducing
protocol procedures and state machines at the same time.
4.1.2. Generalized Topology View
This section and resulting Section 4.2.5.2 are dedicated to multi-
plane fabrics, in contrast with the single plane designs where all
top-of-fabric nodes are topologically equal and initially connected
to all the switches at the level below them.
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It is quite difficult to visualize multi plane design, which are
effectively multi-dimensional switching matrices. To cope with that,
this document introduces a methodology allowing to depict the
connectivity in two-dimensional pictures. Further, the fact can be
leveraged that what is under consideration here are basically stacked
crossbar fabrics where ports align "on top of each other" in a
regular fashion.
A word of caution to the reader; at this point it should be observed
that the language used to describe Clos variations, especially in
multi-plane designs, varies widely between sources. This description
follows the terminology introduced in Section 3.1. It is unavoidable
to have it present to be able to follow the rest of this section
correctly.
4.1.2.1. Terminology and Glossary
This section describes the terminology and acronyms used in the rest
of the text. Though the glossary may not be comprehensible on a
first read, the following sections will gradually introduce the terms
in their proper context.
P:
Denotes the number of PoDs in a topology.
S:
Denotes the number of ToF nodes in a topology.
K:
To simplify the visual aids, notations and further considerations,
implicit assumption is made that the switches are symmetrical,
i.e. equal number ports point northbound and southbound. With
that simplification, K denotes half of the radix of a symmetrical
switch, meaning that the switch has K ports pointing north and K
ports pointing south. K_LEAF (K of a leaf) thus represents both
the number of access ports in a leaf Node and the maximum number
of planes in the fabric, whereas K_TOP (K of a ToP) represents the
number of leaves in the PoD and the number of ports pointing north
in a ToP Node towards a higher spine level, thus the number of ToF
nodes in a plane.
ToF Plane:
Set of ToFs that are aware of each other by means of south
reflection. Planes are numbered by capital letters, e.g. plane
A.
N:
Denotes the number of independent ToF planes in a topology.
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R:
Denotes a redundancy factor, i.e. number of connections a spine
has towards a ToF plane. In single plane design K_TOP is equal to
R.
Fallen Leaf:
A fallen leaf in a plane Z is a switch that lost all connectivity
northbound to Z.
4.1.2.2. Clos as Crossed, Stacked Crossbars
The typical topology for which RIFT is defined is built of P number
of PoDs and connected together by S number of ToF nodes. A PoD node
has K number of ports. From here on half of them (K=Radix/2) are
assumed to connect host devices from the south, and the other half to
connect to interleaved PoD Top-Level switches to the north. The K
ratio can be chosen differently without loss of generality when port
speeds differ or the fabric is oversubscribed but K=Radix/2 allows
for more readable representation whereby there are as many ports
facing north as south on any intermediate node. A node is hence
represented in a schematic fashion with ports "sticking out" to its
north and south rather than by the usual real-world front faceplate
designs of the day.
Figure 4 provides a view of a leaf node as seen from the north, i.e.
showing ports that connect northbound. For lack of a better symbol,
the document chooses to use the "o" as ASCII visualisation of a
single port. In this example, K_LEAF has 6 ports. Observe that the
number of PoDs is not related to Radix unless the ToF Nodes are
constrained to be the same as the PoD nodes in a particular
deployment.
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Top view
+---+
| |
| O | e.g., Radix = 12, K_LEAF = 6
| |
| O |
| | -------------------------
| o <------ Physical Port (Ethernet) ----+
| | ------------------------- |
| O | |
| | |
| O | |
| | |
| O | |
| | |
+---+ v
|| || || || || || ||
+----+ +------------------------------------------------+
| | | |
+----+ +------------------------------------------------+
|| || || || || || ||
Side views
Figure 4: A Leaf Node, K_LEAF=6
The Radix of a PoD's top node may be different than that of the leaf
node. Though, more often than not, a same type of node is used for
both, effectively forming a square (K*K). In the general case,
switches at the top of the PoD with K_TOP southern ports not
necessarily equal to K_LEAF could be considered . For instance, in
the representations below, we pick a 6 port K_LEAF and a 8 port
K_TOP. In order to form a crossbar, K_TOP Leaf Nodes are necessary
as illustrated in Figure 5.
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+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
| | | | | | | | | | | | | | | |
| O | | O | | O | | O | | O | | O | | O | | O |
| | | | | | | | | | | | | | | |
| O | | O | | O | | O | | O | | O | | O | | O |
| | | | | | | | | | | | | | | |
| O | | O | | O | | O | | O | | O | | O | | O |
| | | | | | | | | | | | | | | |
| O | | O | | O | | O | | O | | O | | O | | O |
| | | | | | | | | | | | | | | |
| O | | O | | O | | O | | O | | O | | O | | O |
| | | | | | | | | | | | | | | |
| O | | O | | O | | O | | O | | O | | O | | O |
| | | | | | | | | | | | | | | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
Figure 5: Southern View of a PoD, K_TOP=8
As further visualized in Figure 6 the K_TOP Leaf Nodes are fully
interconnected with the K_LEAF ToP nodes, providing connectivity that
can be represented as a crossbar when "looked at" from the north.
The result is that, in the absence of a failure, a packet entering
the PoD from the north on any port can be routed to any port in the
south of the PoD and vice versa. And that is precisely why it makes
sense to talk about a "switching matrix".
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E<-*->W
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
| | | | | | | | | | | | | | | |
+--------------------------------------------------------+
| o o o o o o o o |
+--------------------------------------------------------+
+--------------------------------------------------------+
| o o o o o o o o |
+--------------------------------------------------------+
+--------------------------------------------------------+
| o o o o o o o o |
+--------------------------------------------------------+
+--------------------------------------------------------+
| o o o o o o o o |
+--------------------------------------------------------+
+--------------------------------------------------------+
| o o o o o o o o |<-+
+--------------------------------------------------------+ |
+--------------------------------------------------------+ |
| o o o o o o o o | |
+--------------------------------------------------------+ |
| | | | | | | | | | | | | | | | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ |
^ |
| |
| ---------- --------------------- |
+----- Leaf Node PoD top Node (Spine) --+
---------- ---------------------
Figure 6: Northern View of a PoD's Spines, K_TOP=8
Side views of this PoD is illustrated in Figure 7 and Figure 8.
Connecting to Spine
|| || || || || || || ||
+----------------------------------------------------------------+ N
| PoD top Nodes seen sideways | ^
+----------------------------------------------------------------+ |
|| || || || || || || || *
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
| | | | | | | | | | | | | | | | v
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ S
|| || || || || || || ||
Connecting to Client nodes
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Figure 7: Side View of a PoD, K_TOP=8, K_LEAF=6
Connecting to Spine
|| || || || || ||
+----+ +----+ +----+ +----+ +----+ +----+ N
| | | | | | | | | | | PoD top Nodes ^
+----+ +----+ +----+ +----+ +----+ +----+ |
|| || || || || || *
+------------------------------------------------+ |
| Leaf seen sideways | v
+------------------------------------------------+ S
Connecting to Client nodes
Figure 8: Other Side View of a PoD, K_TOP=8, K_LEAF=6, 90o turn
in E-W Plane from the previous figure
As next step, observe further that a resulting PoD can be abstracted
as a bigger node with a number K of K_POD= K_TOP * K_LEAF, and the
design can recurse.
It will be critical at this point that, before progressing further,
the concept and the picture of "crossed crossbars" is clear. Else,
the following considerations might be difficult to comprehend.
To continue, the PoDs are interconnected with each other through a
Top-of-Fabric (ToF) node at the very top or the north edge of the
fabric. The resulting ToF is *not* partitioned if, and only if
(IIF), every PoD top level node (spine) is connected to every ToF
Node. This topology is also referred to as a single plane
configuration and is quite popular due to its simplicity. In order
to reach a 1:1 connectivity ratio between the ToF and the leaves, it
results that there are K_TOP ToF nodes, because each port of a ToP
node connects to a different ToF node, and K_LEAF ToP nodes for the
same reason. Consequently, it will take (P * K_LEAF) ports on a ToF
node to connect to each of the K_LEAF ToP nodes of the P PoDs.
Figure 9 illustrates this, looking at P=3 PoDs from above and 2
sides. The large view is the one from above, with the 8 ToF of 3*6
ports each interconnecting the PoDs, every ToP Node being connected
to every ToF node.
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[ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] <-----+
| | | | | | | | |
[=================================] | --------------
| | | | | | | | +----- Top-of-Fabric
[ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] +----- Node -------+
| -------------- |
| v
+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ <-----+ +-+
| | | | | | | | | | | | | | | | | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] ------------------------- | |
[ |o| |o| |o| |o| |o| |o| |o| |o<--- Physical Port (Ethernet) | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] ------------------------- | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | |
| | | | | | | | | | | | | | | | | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] -------------- | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] <--- PoD top level | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] node (Spine) ---+ | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] -------------- | | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | | |
| | | | | | | | | | | | | | | | -+ +- +-+ v | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | | --| |--[ ]--| |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | ----- | --| |--[ ]--| |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] +--- PoD ---+ --| |--[ ]--| |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | ----- | --| |--[ ]--| |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | | --| |--[ ]--| |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | | --| |--[ ]--| |
| | | | | | | | | | | | | | | | -+ +- +-+ | |
+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+
Figure 9: Fabric Spines and TOFs in Single Plane Design, 3 PoDs
The top view can be collapsed into a third dimension where the hidden
depth index is representing the PoD number. One PoD can be shown
then as a class of PoDs and hence save one dimension in the
representation. The Spine Node expands in the depth and the vertical
dimensions, whereas the PoD top level Nodes are constrained, in
horizontal dimension. A port in the 2-D representation represents
effectively the class of all the ports at the same position in all
the PoDs that are projected in its position along the depth axis.
This is shown in Figure 10.
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/ / / / / / / / / / / / / / / /
/ / / / / / / / / / / / / / / /
/ / / / / / / / / / / / / / / /
/ / / / / / / / / / / / / / / / ]
+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ ]]
| | | | | | | | | | | | | | | | ] ---------------------------
[ |o| |o| |o| |o| |o| |o| |o| |o| ] <-- PoD top level node (Spine)
[ |o| |o| |o| |o| |o| |o| |o| |o| ] ---------------------------
[ |o| |o| |o| |o| |o| |o| |o| |o| ]]]]
[ |o| |o| |o| |o| |o| |o| |o| |o| ]]] ^^
[ |o| |o| |o| |o| |o| |o| |o| |o| ]] // PoDs
[ |o| |o| |o| |o| |o| |o| |o| |o| ] // (in depth)
| |/| |/| |/| |/| |/| |/| |/| |/ //
+-+ +-+ +-+/+-+/+-+ +-+ +-+ +-+ //
^
| ----------------
+----- Top-of-Fabric Node
----------------
Figure 10: Collapsed Northern View of a Fabric for Any Number of PoDs
As simple as single plane deployment is, it introduces a limit due to
the bound on the available radix of the ToF nodes that has to be at
least P * K_LEAF. Nevertheless, it will be come clear that a
distinct advantage of a connected or non-partitioned Top-of-Fabric is
that all failures can be resolved by simple, non-transitive, positive
disaggregation (i.e. nodes advertising more specific prefixes with
the default to the level below them that is however not propagated
further down the fabric) as described in Section 4.2.5.1 . In other
words; non-partitioned ToF nodes can always reach nodes below or
withdraw the routes from PoDs they cannot reach unambiguously. And
with this, positive disaggregation can heal all failures and still
allow all the ToF nodes to see each other via south reflection.
Disaggregation will be explained in further detail in Section 4.2.5.
In order to scale beyond the "single plane limit", the Top-of-Fabric
can be partitioned by an N number of identically wired planes where N
is an integer divider of K_LEAF. The 1:1 ratio and the desired
symmetry are still served, this time with (K_TOP * N) ToF nodes, each
of (P * K_LEAF / N) ports. N=1 represents a non-partitioned Spine
and N=K_LEAF is a maximally partitioned Spine. Further, if R is any
integer divisor of K_LEAF, then N=K_LEAF/R is a feasible number of
planes and R a redundancy factor that denotes the number of
independent paths between 2 leaves within a plane. It proves
convenient for deployments to use a radix for the leaf nodes that is
a power of 2 so they can pick a number of planes that is a lower
power of 2. The example in Figure 11 splits the Spine in 2 planes
with a redundancy factor R=3, meaning that there are 3 non-
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intersecting paths between any leaf node and any ToF node. A ToF
node must have, in this case, at least 3*P ports, and be directly
connected to 3 of the 6 ToP nodes (spines) in each PoD. The ToP
nodes are represented horizontally with K_TOP=8 ports northwards
each.
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | O | | O | | O | | O | | O | | O | | O | | O | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | O | | O | | O | | O | | O | | O | | O | | O | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | O | | O | | O | | O | | O | | O | | O | | O | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
Plane 1
----------- . ------------ . ------------ . ------------ . --------
Plane 2
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | O | | O | | O | | O | | O | | O | | O | | O | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | O | | O | | O | | O | | O | | O | | O | | O | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | O | | O | | O | | O | | O | | O | | O | | O | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
^
|
| ----------------
+----- Top-of-Fabric node
"across" depth
----------------
Figure 11: Northern View of a Multi-Plane ToF Level, K_LEAF=6, N=2
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At the extreme end of the spectrum it is even possible to fully
partition the spine with N = K_LEAF and R=1, while maintaining
connectivity between each leaf node and each Top-of-Fabric node. In
that case the ToF node connects to a single Port per PoD, so it
appears as a single port in the projected view represented in
Figure 12. The number of ports required on the Spine Node is more
than or equal to P, the number of PoDs.
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Plane 1
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ -+
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
| | O | | O | | O | | O | | O | | O | | O | | O | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ |
----------- . ------------------- . ------------ . ------- |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
| | O | | O | | O | | O | | O | | O | | O | | O | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ |
----------- . ------------ . ---- . ------------ . ------- |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
| | O | | O | | O | | O | | O | | O | | O | | O | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ |
----------- . ------------ . ------------------- . --------+<-+
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
| | O | | O | | O | | O | | O | | O | | O | | O | | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | |
----------- . ------------ . ------------ . ---- . ------- | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
| | O | | O | | O | | O | | O | | O | | O | | O | | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | |
----------- . ------------ . ------------ . -------------- | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
| | O | | O | | O | | O | | O | | O | | O | | O | | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ -+ |
Plane 6 ^ |
| |
| ---------------- ------------- |
+----- ToF Node Class of PoDs ---+
---------------- -------------
Figure 12: Northern View of a Maximally Partitioned ToF Level, R=1
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4.1.3. Fallen Leaf Problem
As mentioned earlier, RIFT exhibits an anisotropic behavior tailored
for fabrics with a North / South orientation and a high level of
interleaving paths. A non-partitioned fabric makes a total loss of
connectivity between a Top-of-Fabric node at the north and a leaf
node at the south a very rare but yet possible occasion that is fully
healed by positive disaggregation as described in Section 4.2.5.1.
In large fabrics or fabrics built from switches with low radix, the
ToF ends often being partitioned in planes which makes the occurrence
of having a given leaf being only reachable from a subset of the ToF
nodes more likely to happen. This makes some further considerations
necessary.
A "Fallen Leaf" is a leaf that can be reached by only a subset, but
not all, of Top-of-Fabric nodes due to missing connectivity. If R is
the redundancy factor, then it takes at least R breakages to reach a
"Fallen Leaf" situation.
In a maximally partitioned fabric, the redundancy factor is R=1, so
any breakage in the fabric will cause one or more fallen leaves in
the affected plane. R=2 guarantees that a single breakage will not
cause a fallen leaf. However, not all cases require disaggregation.
The following cases do not require particular action:
If a southern link on a node goes down, then connectivity through
that node is lost for all nodes south of it. There is no need to
disaggregate since the connectivity to this node is lost for all
spine nodes in a same fashion.
If a ToF Node goes down, then northern traffic towards it is
routed via alternate ToF nodes in the same plane and there is no
need to disaggregate routes.
In a general manner, the mechanism of non-transitive positive
disaggregation is sufficient when the disaggregating ToF nodes
collectively connect to all the ToP nodes in the broken plane. This
happens in the following case:
If the breakage is the last northern link from a ToP node to a ToF
node going down, then the fallen leaf problem affects only the ToF
node, and the connectivity to all the nodes in the PoD is lost
from that ToF node. This can be observed by other ToF nodes
within the plane where the ToP node is located and positively
disaggregated within that plane.
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On the other hand, there is a need to disaggregate the routes to
Fallen Leaves within the plane in a transitive fashion, that is, all
the way to the other leaves, in the following cases:
* If the breakage is the last northern link from a leaf node within
a plane (there is only one such link in a maximally partitioned
fabric) that goes down, then connectivity to all unicast prefixes
attached to the leaf node is lost within the plane where the link
is located. Southern Reflection by a leaf node, e.g., between ToP
nodes, if the PoD has only 2 levels, happens in between planes,
allowing the ToP nodes to detect the problem within the PoD where
it occurs and positively disaggregate. The breakage can be
observed by the ToF nodes in the same plane through the North
flooding of TIEs from the ToP nodes. The ToF nodes however need
to be aware of all the affected prefixes for the negative,
possibly transitive disaggregation to be fully effective (i.e. a
node advertising in the control plane that it cannot reach a
certain more specific prefix than default whereas such
disaggregation must in the extreme condition propagate further
down southbound). The problem can also be observed by the ToF
nodes in the other planes through the flooding of North TIEs from
the affected leaf nodes, together with non-node North TIEs which
indicate the affected prefixes. To be effective in that case, the
positive disaggregation must reach down to the nodes that make the
plane selection, which are typically the ingress leaf nodes. The
information is not useful for routing in the intermediate levels.
* If the breakage is a ToP node in a maximally partitioned fabric
(in which case it is the only ToP node serving the plane in that
PoD that goes down), then the connectivity to all the nodes in the
PoD is lost within the plane where the ToP node is located.
Consequently, all leaves of the PoD fall in this plane. Since the
Southern Reflection between the ToF nodes happens only within a
plane, ToF nodes in other planes cannot discover fallen leaves in
a different plane. They also cannot determine beyond their local
plane whether a leaf node that was initially reachable has become
unreachable. As the breakage can be observed by the ToF nodes in
the plane where the breakage happened, the ToF nodes in the plane
need to be aware of all the affected prefixes for the negative
disaggregation to be fully effective. The problem can also be
observed by the ToF nodes in the other planes through the flooding
of North TIEs from the affected leaf nodes, if there are only 3
levels and the ToP nodes are directly connected to the leaf nodes,
and then again it can only be effective it is propagated
transitively to the leaf, and useless above that level.
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For the sake of easy comprehension the abstractions are rolled back
into a simple example that shows that in Figure 3 the loss of link
Spine 122 to Leaf 122 will make Leaf 122 a fallen leaf for Top-of-
Fabric plane B. Worse, if the cabling was never present in the first
place, plane B will not even be able to know that such a fallen leaf
exists. Hence partitioning without further treatment results in two
grave problems:
* Leaf 111 trying to route to Leaf 122 must choose Spine 111 in
plane A as its next hop since plane B will inevitably blackhole
the packet when forwarding using default routes or do excessive
bow tying. This information must be in its routing table.
* A path computation trying to deal with the problem by distributing
host routes may only form paths through leaves. The flooding of
information about Leaf 122 would have to go up to Top-of-Fabric A
and then "loopback" over other leaves to ToF B leading in extreme
cases to traffic for Leaf 122 when presented to plane B taking an
"inverted fabric" path where leaves start to serve as TOFs, at
least for the duration of a protocol's convergence.
4.1.4. Discovering Fallen Leaves
When aggregation is used, RIFT deals with fallen leaves by ensuring
that all the ToF nodes share the same north topology database. This
happens naturally in single plane design by the means of northbound
flooding and south reflection but needs additional considerations in
multi-plane fabrics. To enable routing to fallen leaves in multi-
plane designs, RIFT requires additional interconnection across planes
between the ToF nodes, e.g., using rings as illustrated in Figure 13.
Other solutions are possible but they either need more cabling or end
up having much longer flooding paths and/or single points of failure.
In detail, by reserving two ports on each Top-of-Fabric node it is
possible to connect them together by interplane bi-directional rings
as illustrated in Figure 13. The rings will be used to exchange full
north topology information between planes. All ToFs having same
north topology allows by the means of transitive, negative
disaggregation described in Section 4.2.5.2 to efficiently fix any
possible fallen leaf scenario. Somewhat as a side-effect, the
exchange of information fulfills the requirement to have a full view
of the fabric topology at the Top-of-Fabric level, without the need
to collate it from multiple points.
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+---+ +---+ +---+ +---+ +---+ +---+ +--------+
| | | | | | | | | | | | | |
| | | | | | | |
+-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ |
+-| |--| |--| |--| |--| |--| |--| |-+ |
| | o | | o | | o | | o | | o | | o | | o | | | Plane A
+-| |--| |--| |--| |--| |--| |--| |-+ |
+-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ |
| | | | | | | |
+-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ |
+-| |--| |--| |--| |--| |--| |--| |-+ |
| | o | | o | | o | | o | | o | | o | | o | | | Plane B
+-| |--| |--| |--| |--| |--| |--| |-+ |
+-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ |
| | | | | | | |
... |
| | | | | | | |
+-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ |
+-| |--| |--| |--| |--| |--| |--| |-+ |
| | o | | o | | o | | o | | o | | o | | o | | | Plane X
+-| |--| |--| |--| |--| |--| |--| |-+ |
+-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ |
| | | | | | | |
| | | | | | | | | | | | | |
+---+ +---+ +---+ +---+ +---+ +---+ +--------+
Rings 1 2 3 4 5 6 7
Figure 13: Using rings to bring all planes and at the ToF bind them
4.1.5. Addressing the Fallen Leaves Problem
One consequence of the "Fallen Leaf" problem is that some prefixes
attached to the fallen leaf become unreachable from some of the ToF
nodes. RIFT defines two methods to address this issue, the positive
and the negative disaggregation. Both methods flood according types
of South TIEs to advertise the impacted prefix(es).
When used for the operation of disaggregation, a positive South TIE
contained in `positive_disaggregation_prefixes`, as usual, indicates
reachability to a prefix of given length and all addresses subsumed
by it. In contrast, a negative route advertisement contained in
`negative_disaggregation_prefixes` indicates that the origin cannot
route to the advertised prefix.
The positive disaggregation is originated by a router that can still
reach the advertised prefix, and the operation is not transitive. In
other words, the receiver does *not* generate its own TIEs or floods
them south as a consequence of receiving positive disaggregation
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advertisements from a higher level node. The effect of a positive
disaggregation is that the traffic to the impacted prefix will follow
the longest match and will be limited to the northbound routers that
advertised the more specific route.
In contrast, the negative disaggregation can be transitive, and is
propagated south when all the possible routes have been advertised as
negative exceptions. A negative route advertisement is only
actionable when the negative prefix is aggregated by a positive route
advertisement for a shorter prefix. In such case, the negative
advertisement "punches out a hole" in the positive route in the
routing table, making the positive prefix reachable through the
originator with the special consideration of the negative prefix
removing certain next hop neighbors. The specific procedures will be
explained in detail in Section 4.2.5.2.3.
When the top of fabric switches are not partitioned into multiple
planes, the resulting southbound flooding of the positive
disaggregation by the ToF nodes that can still reach the impacted
prefix is in general enough to cover all the switches at the next
level south, typically the ToP nodes. If all those switches are
aware of the disaggregation, they collectively create a ceiling that
intercepts all the traffic north and forwards it to the ToF nodes
that advertised the more specific route. In that case, the positive
disaggregation alone is sufficient to solve the fallen leaf problem.
On the other hand, when the fabric is partitioned in planes, the
positive disaggregation from ToF nodes in different planes do not
reach the ToP switches in the affected plane and cannot solve the
fallen leaves problem. In other words, a breakage in a plane can
only be solved in that plane. Also, the selection of the plane for a
packet typically occurs at the leaf level and the disaggregation must
be transitive and reach all the leaves. In that case, the negative
disaggregation is necessary. The details on the RIFT approach to
deal with fallen leaves in an optimal way are specified in
Section 4.2.5.2.
4.2. Specification
This section specifies the protocol in a normative fashion by either
prescriptive procedures or behavior defined by Finite State Machines
(FSM).
The FSMs, as usual, are presented as states the FSM can assume,
events that it can be given and according actions performed when
transitioning between states on event processing.
Actions are performed before the end state is assumed.
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The FSMs can queue events against itself to chain actions or against
other FSMs in the specification. Events are always processed in the
sequence they have been queued.
Consequently, "On Entry" actions on FSM state are performed every
time and right before the according state is entered, i.e. after any
transitions from previous state.
"On Exit" actions are performed every time and immediately when a
state is exited, i.e. before any transitions towards target state are
performed.
Any attempt to transition from a state towards another on reception
of an event where no action is specified MUST be considered an
unrecoverable error, i.e. the protocol MUST reset all adjacencies,
discard all the state and MAY NOT start again.
The data structures and FSMs described in this document are
conceptual and do not have to be implemented precisely as described
here, as long as the implementations support the described
functionality and exhibit the same externally visible behavior.
The machines can use conceptually "timers" for different situations.
Those timers are started through actions and their expiration leads
to queuing of according events to be processed.
The term `holdtime` is used often as short-hand for `holddown timer`
and signifies either the length of the holding down period or the
timer used to expire after such period. Such timers are used to
"hold down" state within an FSM that is cleaned if the machine
triggers a `HoldtimeExpired` event.
4.2.1. Transport
All packet formats are defined in Thrift [thrift] models in
Appendix B. LIE packet format is contained in the `LIEPacket` schema
element. TIE packet format is contained in `TIEPacket`, TIDE and
TIRE accordingly in `TIDEPacket`, `TIREPacket` and the whole packet
is a union of the above in `ProtocolPacket` while it contains a
`PacketHeader` as well.
Such a packet being in terms of bits on the wire a serialized
`ProtocolPacket` is carried in an envelope defined in Section 4.4.3
within a UDP frame that provides security and allows validation/
modification of several important fields without de-serialization for
performance and security reasons. Security model and procedures are
further explained in Section 7.
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4.2.2. Link (Neighbor) Discovery (LIE Exchange)
RIFT LIE exchange auto-discovers neighbors, negotiates ZTP parameters
and discovers miscablings. The formation progresses under normal
conditions from OneWay to TwoWay and then ThreeWay state at which
point it is ready to exchange TIEs per Section 4.2.3. The adjacency
exchanges ZTP information (Section 4.2.7) in any of the states, i.e.
it is not necessary to reach ThreeWay for zero-touch provisioning to
operate.
RIFT supports any combination of IPv4 and IPv6 addressing on the
fabric with the additional capability for forwarding paths that are
capable of forwarding IPv4 packets in presence of IPv6 addressing
only.
For IPv4 LIE exchange happens over well-known administratively
locally scoped and configured or otherwise well-known IPv4 multicast
address [RFC2365]. For IPv6 [RFC8200] exchange is performed over
link-local multicast scope [RFC4291] address which is configured or
otherwise well-known. In both cases a destination UDP port defined
in Appendix C.1 is used unless configured otherwise. LIEs SHOULD be
sent with an IPv4 Time to Live (TTL) / IPv6 Hop Limit (HL) of either
1 or 255 to prevent RIFT information reaching beyond a single L3
next-hop in the topology. LIEs SHOULD be sent with network control
precedence unless an implementation is prevented from doing so.
The originating port of the LIE has no further significance other
than identifying the origination point. LIEs are exchanged over all
links running RIFT.
An implementation MAY listen and send LIEs on IPv4 and/or IPv6
multicast addresses. A node MUST NOT originate LIEs on an address
family if it does not process received LIEs on that family. LIEs on
same link are considered part of the same LIE FSM independent of the
address family they arrive on. Observe further that the LIE source
address may not identify the peer uniquely in unnumbered or link-
local address cases so the response transmission MUST occur over the
same interface the LIEs have been received on. A node MAY use any of
the adjacency's source addresses it saw in LIEs on the specific
interface during adjacency formation to send TIEs (Section 4.2.3.3).
That implies that an implementation MUST be ready to accept TIEs on
all addresses it used as source of LIE frames.
A ThreeWay adjacency (as defined in the glossary) over any address
family implies support for IPv4 forwarding if the
`ipv4_forwarding_capable` flag in `LinkCapabilities` is set to true.
A node, in case of absence of IPv4 addresses on such links and
advertising `ipv4_forwarding_capable` as true, MUST forward IPv4
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packets using gateways discovered on IPv6-only links advertising this
capability. It is expected that the whole fabric supports the same
type of forwarding of address families on all the links, any other
combination is outside the scope of this specification.
`ipv4_forwarding_capable` MUST be set to true when LIEs from a IPv4
address are sent and MAY be set to true in LIEs on IPv6 address if no
LIEs are sent from a IPv4 address. If IPv4 and IPv6 LIEs indicate
contradicting information protocol behavior is unspecified.
Operation of a fabric where only some of the links are supporting
forwarding on an address family or have an address in a family and
others do not is outside the scope of this specification.
Any attempt to construct IPv6 forwarding over IPv4 only adjacencies
is outside this specification.
Table 1 outlines protocol behavior in case of different address
family combinations.
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+=======+=======+=============================================+
| AF | AF | Behavior |
+=======+=======+=============================================+
| IPv4 | IPv4 | LIEs and TIEs are exchanged over IPv4, no |
| | | IPv6 forwarding. TIEs are received on any |
| | | of the LIE sending addresses. |
+-------+-------+---------------------------------------------+
| IPv6 | IPv6 | LIEs and TIEs are exchanged over IPv6 only, |
| | | no IPv4 forwarding if either of the |
| | | `ipv4_forwarding_capable` flags is false. |
| | | If both `ipv4_forwarding_capable` flags are |
| | | true IPv4 is forwarded. TIEs are received |
| | | on any of the LIE sending addresses. |
+-------+-------+---------------------------------------------+
| IPv4, | IPv6 | LIEs and TIEs are exchanged over IPv6, no |
| IPv6 | | IPv4 forwarding if either of the |
| | | `ipv4_forwarding_capable` flags is false. |
| | | If both `ipv4_forwarding_capable` are true |
| | | IPv4 is forwarded. TIEs are received on |
| | | any of the IPv6 LIE sending addresses. |
+-------+-------+---------------------------------------------+
| IPv4, | IPv4, | LIEs and TIEs are exchanged over IPv6 and |
| IPv6 | IPv6 | IPv4, unspecified behavior if either of the |
| | | `ipv4_forwarding_capable` flags is false or |
| | | IPv4 and IPv6 advertise different flags as |
| | | described previously. IPv4 and IPv6 are |
| | | forwarded. TIEs are received on any of the |
| | | IPv4 and IPv6 LIE sending addresses. |
+-------+-------+---------------------------------------------+
Table 1: Neighbor AF Combination Behavior
The protocol does *not* support selective disabling of address
families after adjacency formation, disabling IPv4 forwarding
capability or any local address changes in ThreeWay state, i.e. if a
link has entered ThreeWay IPv4 and/or IPv6 with a neighbor on an
adjacency and it wants to stop supporting one of the families or
change any of its local addresses or stop IPv4 forwarding, it has to
tear down and rebuild the adjacency. It also has to remove any state
it stored about the remote side of the adjacency such as LIE source
addresses seen.
Unless ZTP as described in Section 4.2.7 is used, each node is
provisioned with the level at which it is operating and advertises it
in the `level` of the `PacketHeader` schema element. It MAY be also
provisioned with its PoD. If level is not provisioned it is not
present in the optional `PacketHeader` schema element and established
by ZTP procedures if feasible. If PoD is not provisioned it is as
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governed by the `LIEPacket` schema element assuming the
`common.default_pod` value. This means that switches except top of
fabric do not need to be configured at all. Necessary information to
configure all values is exchanged in the `LIEPacket` and
`PacketHeader` or derived by the node automatically.
Further definitions of leaf flags are found in Section 4.2.7 given
they have implications in terms of level and adjacency forming here.
Leaf flags are carried in `HierarchyIndications`.
A node MUST form a ThreeWay adjacency (or in other words consider the
neighbor "valid" and hence reflecting it) if and only if the
following first order logic conditions are satisfied on a LIE packet
as specified by the `LIEPacket` schema element and received on a link
1. the neighboring node is running the same major schema version as
indicated in the `major_version` element in `PacketHeader` *and*
2. the neighboring node uses a valid System ID (i.e. value different
from `IllegalSystemID`) in `sender` element in `PacketHeader`
*and*
3. the neighboring node uses a different System ID than the node
itself
4. the advertised MTUs in `LiePacket` element match on both sides
*and*
5. both nodes advertise defined level values in `level` element in
`PacketHeader` *and*
6. [
i) the node is at `leaf_level` value and has no ThreeWay
adjacencies already to nodes at Highest Adjacency ThreeWay
(HAT as defined later in Section 4.2.7.1) with level different
than the adjacent node *or*
ii) the node is not at `leaf_level` value and the neighboring
node is at `leaf_level` value *or*
iii) both nodes are at `leaf_level` values *and* both indicate
support for Section 4.3.9 *or*
iv) neither node is at `leaf_level` value and the neighboring
node is at most one level difference away
].
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LIEs arriving with IPv4 Time to Live (TTL) / IPv6 Hop Limit (HL)
different than 1 or 255 SHOULD be ignored.
4.2.2.1. LIE Finite State Machine
This section specifies the precise, normative LIE FSM. For easier
reference the according figure is given as well in Figure 14.
Additionally, some sets of actions repeat often and are hence
summarized into well-known procedures.
Events generated are fairly fine grained, especially when indicating
problems in adjacency forming conditions. The intention of such
differentiation is to simplify tracking of problems in deployment.
Initial state is `OneWay`.
The machine sends LIEs proactively on several transitions to
accelerate adjacency bring-up without waiting for the according timer
tic.
Enter
|
V
+-----------+
| OneWay |<----+
| | | HALChanged
| | | HALSChanged
| | | HATChanged
| | | HoldTimerExpired
| | | InstanceNameMismatch
| | | LevelChanged
| | | LieRcvd
| | | MTUMismatch
| | | NeighborChangedAddress
| | | NeighborChangedLevel
| | | NeighborChangedMinorFields
| | | NeighborDroppedReflection
| | | SendLIE
| | | TimerTick
| | | UnacceptableHeader
| | | UpdateZTPOffer
| |-----+
| |
| |<--------------------- (ThreeWay)
| |--------------------->
| | ValidReflection
| |
| |---------------------> (Multiple
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| | MultipleNeighbors Neighbors
+-----------+ Wait)
^ |
| |
| | NewNeighbor
| V
(TwoWay)
(OneWay)
| ^
| | HoldTimeExpired
| | InstanceNameMismatch
| | MTUMismatch
| | NeighborChangedAddress
| | NeighborChangedLevel
| | UnacceptableHeader
V |
+-----------+
| TwoWay |<----+
| | | HALChanged
| | | HALSChanged
| | | HATChanged
| | | LevelChanged
| | | LIERcvd
| | | SendLIE
| | | TimerTick
| | | UpdateZTPOffer
| | | FloodLeadersChanged
| |-----+
| |
| |<----------------------
| |----------------------> (Multiple
| | NewNeighbor Neighbors
| | Wait)
| | MultipleNeighbors
+-----------+
^ |
| | ValidReflection
| V
(ThreeWay)
(TwoWay) (OneWay)
^ | ^
| | | HoldTimerExpired
| | | InstanceNameMismatch
| | | LevelChanged
| | | MTUMismatch
| | | NeighborChangedAddress
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| | | NeighborChangedLevel
NeighborDropped- | | | UnacceptableHeader
Reflection | | |
| V |
+-----------+ |
| ThreeWay |-----+
| |
| |<----+
| | | HALChanged
| | | HALSChanged
| | | HATChanged
| | | LieRcvd
| | | SendLIE
| | | TimerTick
| | | UpdateZTPOffer
| | | ValidReflection
| | | FloodLeadersChanged
| |-----+
| |----------------------> (Multiple
| | MultipleNeighbors Neighbors
+-----------+ Wait)
(TwoWay) (ThreeWay)
| |
V V
+------------+
| Multiple |<----+
| Neighbors | | HALChanged
| Wait | | HALSChanged
| | | HATChanged
| | | MultipleNeighbors
| | | TimerTick
| | | UpdateZTPOffer
| | | FloodLeadersChanged
| | | NeighborChangedAddress
| | | UnacceptableHeader
| | | SendLie
| | | MTUMismatch
| | | LieRcvd
| | | NeighborDroppedReflection
| | |
| | |
| |-----+
| |
| |<---------------------------
| |---------------------------> (OneWay)
| | LevelChanged
+------------+ MultipleNeighborsDone
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Figure 14: LIE FSM
The following words are used for well known procedures:
* PUSH Event: queues an event to be executed by the FSM upon exit of
this action
* CLEANUP: neighbor MUST be reset to unknown
* SEND_LIE: create and send a new LIE packet
1. reflecting the neighbor if known and valid and
2. setting the necessary `not_a_ztp_offer` variable if level was
derived from last known neighbor on this interface and
3. setting `you_are_not_flood_repeater` to computed value
* PROCESS_LIE:
1. if LIE has major version not equal to this node's *or* system
ID equal to this node's system ID or `IllegalSystemID` then
CLEANUP else
2. if LIE has non matching MTUs then CLEANUP, PUSH
UpdateZTPOffer, PUSH MTUMismatch else
3. if LIE has undefined level OR this node's level is undefined
OR this node is a leaf and remote level is lower than HAT OR
(LIE's level is not leaf AND its difference is more than one
from this node's level) then CLEANUP, PUSH UpdateZTPOffer,
PUSH UnacceptableHeader else
4. PUSH UpdateZTPOffer, construct temporary new neighbor
structure with values from LIE, if no current neighbor exists
then set neighbor to new neighbor, PUSH NewNeighbor event,
CHECK_THREE_WAY else
1. if current neighbor system ID differs from LIE's system ID
then PUSH MultipleNeighbors else
2. if current neighbor stored level differs from LIE's level
then PUSH NeighborChangedLevel else
3. if current neighbor stored IPv4/v6 address differs from
LIE's address then PUSH NeighborChangedAddress else
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4. if any of neighbor's flood address port, name, local
LinkID changed then PUSH NeighborChangedMinorFields
5. CHECK_THREE_WAY
* CHECK_THREE_WAY: if current state is OneWay do nothing else
1. if LIE packet does not contain neighbor then if current state
is ThreeWay then PUSH NeighborDroppedReflection else
2. if packet reflects this system's ID and local port and state
is ThreeWay then PUSH event ValidReflection else PUSH event
MultipleNeighbors
States:
* OneWay: initial state FSM is starting from. In this state the
neighbors did not see any valid LIEs from a neighbor after the
state was entered.
* TwoWay: that state is entered when a node has seen a LIE from a
neighbor but it did not contain its reflection.
* ThreeWay: this state signifies that lies from a neighbor are seen
with correct reflection. On achieving this state the link can be
advertised in `neighbors` element in `NodeTIEElement`.
* MultipleNeighborsWait: occurs normally when more than two nodes
see each other on the same link or a remote node is quickly
reconfigured or rebooted without regressing to `OneWay` first.
Each occurrence of the event SHOULD generate a clear, according
notification to help operational deployments.
Events:
* TimerTick: one second timer tic, i.e. the event is generated for
FSM by some external entity once a second. To be quietly ignored
if transition does not exist.
* LevelChanged: node's level has been changed by ZTP or
configuration. This is provided by the ZTP FSM.
* HALChanged: best HAL computed by ZTP has changed. This is
provided by the ZTP FSM.
* HATChanged: HAT computed by ZTP has changed. This is provided by
the ZTP FSM.
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* HALSChanged: set of HAL offering systems computed by ZTP has
changed. This is provided by the ZTP FSM.
* LieRcvd: received LIE on the interface.
* NewNeighbor: new neighbor seen on the received LIE.
* ValidReflection: received reflection of this node from neighbor,
i.e. `neighbor` element in `LiePacket` corresponds to this node.
* NeighborDroppedReflection: lost previously seen reflection from
neighbor, i.e. `neighbor` element in `LiePacket` does not
correspond to this node or is not present.
* NeighborChangedLevel: neighbor changed advertised level from the
previously seen one.
* NeighborChangedAddress: neighbor changed IP address, i.e. LIE has
been received from an address different from previous LIEs. Those
changes will influence the sockets used to listen to TIEs, TIREs,
TIDEs.
* UnacceptableHeader: Unacceptable header seen.
* MTUMismatch: MTU mismatched.
* NeighborChangedMinorFields: minor fields changed in neighbor's
LIE.
* HoldtimeExpired: adjacency holddown timer expired.
* MultipleNeighbors: more than one neighbor seen on interface
* MultipleNeighborsDone: multiple neighbors timer expired.
* FloodLeadersChanged: node's election algorithm determined new set
of flood leaders.
* SendLie: send a LIE out.
* UpdateZTPOffer: update this node's ZTP offer. This is sent to the
ZTP FSM.
Actions:
* on TimerTick in OneWay finishes in OneWay: PUSH SendLie event
* on UnacceptableHeader in OneWay finishes in OneWay: no action
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* on LevelChanged in OneWay finishes in OneWay: update level with
event value, PUSH SendLie event
* on NeighborChangedMinorFields in OneWay finishes in OneWay: no
action
* on NeighborChangedLevel in OneWay finishes in OneWay: no action
* on NewNeighbor in OneWay finishes in TwoWay: PUSH SendLie event
* on HoldtimeExpired in OneWay finishes in OneWay: no action
* on HALSChanged in OneWay finishes in OneWay: store HALS
* on NeighborChangedAddress in OneWay finishes in OneWay: no action
* on LieRcvd in OneWay finishes in OneWay: PROCESS_LIE
* on ValidReflection in OneWay finishes in ThreeWay: no action
* on SendLie in OneWay finishes in OneWay: SEND_LIE
* on UpdateZTPOffer in OneWay finishes in OneWay: send offer to ZTP
FSM
* on HATChanged in OneWay finishes in OneWay: store HAT
* on MultipleNeighbors in OneWay finishes in MultipleNeighborsWait:
start multiple neighbors timer with interval
`multiple_neighbors_lie_holdtime_multipler` *
`default_lie_holdtime`
* on MTUMismatch in OneWay finishes in OneWay: no action
* on FloodLeadersChanged in OneWay finishes in OneWay: update
`you_are_flood_repeater` LIE elements based on flood leader
election results
* on NeighborDroppedReflection in OneWay finishes in OneWay: no
action
* on HALChanged in OneWay finishes in OneWay: store new HAL
* on NeighborChangedAddress in TwoWay finishes in OneWay: no action
* on LieRcvd in TwoWay finishes in TwoWay: PROCESS_LIE
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* on UpdateZTPOffer in TwoWay finishes in TwoWay: send offer to ZTP
FSM
* on HoldtimeExpired in TwoWay finishes in OneWay: no action
* on MTUMismatch in TwoWay finishes in OneWay: no action
* on UnacceptableHeader in TwoWay finishes in OneWay: no action
* on ValidReflection in TwoWay finishes in ThreeWay: no action
* on SendLie in TwoWay finishes in TwoWay: SEND_LIE
* on HATChanged in TwoWay finishes in TwoWay: store HAT
* on HALChanged in TwoWay finishes in TwoWay: store new HAL
* on LevelChanged in TwoWay finishes in TwoWay: update level with
event value
* on FloodLeadersChanged in TwoWay finishes in TwoWay: update
`you_are_flood_repeater` LIE elements based on flood leader
election results
* on NewNeighbor in TwoWay finishes in MultipleNeighborsWait: PUSH
SendLie event
* on TimerTick in TwoWay finishes in TwoWay: PUSH SendLie event, if
last valid LIE was received more than `holdtime` ago as advertised
by neighbor then PUSH HoldtimeExpired event
* on NeighborChangedLevel in TwoWay finishes in OneWay: no action
* on MultipleNeighbors in TwoWay finishes in MultipleNeighborsWait:
start multiple neighbors timer with interval
`multiple_neighbors_lie_holdtime_multipler` *
`default_lie_holdtime`
* on HALSChanged in TwoWay finishes in TwoWay: store HALS
* on NeighborChangedAddress in ThreeWay finishes in OneWay: no
action
* on ValidReflection in ThreeWay finishes in ThreeWay: no action
* on HoldtimeExpired in ThreeWay finishes in OneWay: no action
* on UnacceptableHeader in ThreeWay finishes in OneWay: no action
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* on NeighborDroppedReflection in ThreeWay finishes in TwoWay: no
action
* on HALChanged in ThreeWay finishes in ThreeWay: store new HAL
* on MultipleNeighbors in ThreeWay finishes in
MultipleNeighborsWait: start multiple neighbors timer with
interval `multiple_neighbors_lie_holdtime_multipler` *
`default_lie_holdtime`
* on LevelChanged in ThreeWay finishes in OneWay: update level with
event value
* on HALSChanged in ThreeWay finishes in ThreeWay: store HALS
* on TimerTick in ThreeWay finishes in ThreeWay: PUSH SendLie event,
if last valid LIE was received more than `holdtime` ago as
advertised by neighbor then PUSH HoldtimeExpired event
* on HATChanged in ThreeWay finishes in ThreeWay: store HAT
* on UpdateZTPOffer in ThreeWay finishes in ThreeWay: send offer to
ZTP FSM
* on LieRcvd in ThreeWay finishes in ThreeWay: PROCESS_LIE
* on NeighborChangedLevel in ThreeWay finishes in OneWay: no action
* on SendLie in ThreeWay finishes in ThreeWay: SEND_LIE
* on FloodLeadersChanged in ThreeWay finishes in ThreeWay: update
`you_are_flood_repeater` LIE elements based on flood leader
election results, PUSH SendLie
* on MTUMismatch in ThreeWay finishes in OneWay: no action
* on HoldtimeExpired in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
* on LieRcvd in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
* on NeighborDroppedReflection in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
* on MTUMismatch in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
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* on NeighborChangedBFDCapability in MultipleNeighborsWait finishes
in MultipleNeighborsWait: no action
* on LevelChanged in MultipleNeighborsWait finishes in OneWay:
update level with event value
* on SendLie in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
* on UpdateZTPOffer in MultipleNeighborsWait finishes in
MultipleNeighborsWait: send offer to ZTP FSM
* on MultipleNeighborsDone in MultipleNeighborsWait finishes in
OneWay: no action
* on HATChanged in MultipleNeighborsWait finishes in
MultipleNeighborsWait: store HAT
* on NeighborChangedAddress in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
* on HALSChanged in MultipleNeighborsWait finishes in
MultipleNeighborsWait: store HALS
* on HALChanged in MultipleNeighborsWait finishes in
MultipleNeighborsWait: store new HAL
* on MultipleNeighbors in MultipleNeighborsWait finishes in
MultipleNeighborsWait: start multiple neighbors timer with
interval `multiple_neighbors_lie_holdtime_multipler` *
`default_lie_holdtime`
* on FloodLeadersChanged in MultipleNeighborsWait finishes in
MultipleNeighborsWait: update `you_are_flood_repeater` LIE
elements based on flood leader election results
* on ValidReflection in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
* on TimerTick in MultipleNeighborsWait finishes in
MultipleNeighborsWait: check MultipleNeighbors timer, if timer
expired PUSH MultipleNeighborsDone
* on UnacceptableHeader in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
* on Entry into OneWay: CLEANUP
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4.2.3. Topology Exchange (TIE Exchange)
4.2.3.1. Topology Information Elements
Topology and reachability information in RIFT is conveyed by the
means of TIEs.
The TIE exchange mechanism uses the port indicated by each node in
the LIE exchange as `flood_port` in `LIEPacket` and the interface on
which the adjacency has been formed as destination. It SHOULD use
TTL of 1 or 255 as well and set inter-network control precedence on
according packets.
TIEs contain sequence numbers, lifetimes and a type. Each type has
ample identifying number space and information is spread across
possibly many TIEs of a certain type by the means of a hash function
that an implementation can individually determine. One extreme
design choice is a prefix per TIE which leads to more BGP-like
behavior where small increments are only advertised on route changes
vs. deploying with dense prefix packing into few TIEs leading to more
traditional IGP trade-off with fewer TIEs. An implementation may
even rehash prefix to TIE mapping at any time at the cost of
significant amount of re-advertisements of TIEs.
More information about the TIE structure can be found in the schema
in Appendix B starting with `TIEPacket` root.
4.2.3.2. Southbound and Northbound TIE Representation
A central concept of RIFT is that each node represents itself
differently depending on the direction in which it is advertising
information. More precisely, a spine node represents two different
databases over its adjacencies depending whether it advertises TIEs
to the north or to the south/east-west. Those differing TIE
databases are called either south- or northbound (South TIEs and
North TIEs) depending on the direction of distribution.
The North TIEs hold all of the node's adjacencies and local prefixes
while the South TIEs hold only all of the node's adjacencies, the
default prefix with necessary disaggregated prefixes and local
prefixes. Section 4.2.5 explains further details.
The TIE types are mostly symmetric in both directions and Table 2
provides a quick reference to main TIE types including direction and
their function. The direction itself is carried in `direction` of
`TIEID` schema element.
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+=========================+=================================+
| TIE-Type | Content |
+=========================+=================================+
| Node North TIE | node properties and adjacencies |
+-------------------------+---------------------------------+
| Node South TIE | same content as node North TIE |
+-------------------------+---------------------------------+
| Prefix North TIE | contains nodes' directly |
| | reachable prefixes |
+-------------------------+---------------------------------+
| Prefix South TIE | contains originated defaults |
| | and directly reachable prefixes |
+-------------------------+---------------------------------+
| Positive Disaggregation | contains disaggregated prefixes |
| South TIE | |
+-------------------------+---------------------------------+
| Negative Disaggregation | contains special, negatively |
| South TIE | disaggregated prefixes to |
| | support multi-plane designs |
+-------------------------+---------------------------------+
| External Prefix North | contains external prefixes |
| TIE | |
+-------------------------+---------------------------------+
| Key-Value North TIE | contains nodes northbound KVs |
+-------------------------+---------------------------------+
| Key-Value South TIE | contains nodes southbound KVs |
+-------------------------+---------------------------------+
Table 2: TIE Types
As an example illustrating a databases holding both representations,
the topology in Figure 2 with the optional link between spine 111 and
spine 112 (so that the flooding on an East-West link can be shown) is
considered. Unnumbered interfaces are implicitly assumed and for
simplicity, the key value elements which may be included in their
South TIEs or North TIEs are not shown. First, in Figure 15 are the
TIEs generated by some nodes.
ToF 21 South TIEs:
Node South TIE:
NodeElement(level=2, neighbors((Spine 111, level 1, cost 1),
(Spine 112, level 1, cost 1), (Spine 121, level 1, cost 1),
(Spine 122, level 1, cost 1)))
Prefix South TIE:
SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1))
Spine 111 South TIEs:
Node South TIE:
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NodeElement(level=1, neighbors((ToF 21, level 2, cost 1,
links(...)),
(ToF 22, level 2, cost 1, links(...)),
(Spine 112, level 1, cost 1, links(...)),
(Leaf111, level 0, cost 1, links(...)),
(Leaf112, level 0, cost 1, links(...))))
Prefix South TIE:
SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1))
Spine 111 North TIEs:
Node North TIE:
NodeElement(level=1,
neighbors((ToF 21, level 2, cost 1, links(...)),
(ToF 22, level 2, cost 1, links(...)),
(Spine 112, level 1, cost 1, links(...)),
(Leaf111, level 0, cost 1, links(...)),
(Leaf112, level 0, cost 1, links(...))))
Prefix North TIE:
NorthPrefixesElement(prefixes(Spine 111.loopback)
Spine 121 South TIEs:
Node South TIE:
NodeElement(level=1, neighbors((ToF 21,level 2,cost 1),
(ToF 22, level 2, cost 1), (Leaf121, level 0, cost 1),
(Leaf122, level 0, cost 1)))
Prefix South TIE:
SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1))
Spine 121 North TIEs:
Node North TIE:
NodeElement(level=1,
neighbors((ToF 21, level 2, cost 1, links(...)),
(ToF 22, level 2, cost 1, links(...)),
(Leaf121, level 0, cost 1, links(...)),
(Leaf122, level 0, cost 1, links(...))))
Prefix North TIE:
NorthPrefixesElement(prefixes(Spine 121.loopback)
Leaf112 North TIEs:
Node North TIE:
NodeElement(level=0,
neighbors((Spine 111, level 1, cost 1, links(...)),
(Spine 112, level 1, cost 1, links(...))))
Prefix North TIE:
NorthPrefixesElement(prefixes(Leaf112.loopback, Prefix112,
Prefix_MH))
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Figure 15: Example TIES Generated in a 2 Level Spine-and-Leaf
Topology
It may be here not necessarily obvious why the node South TIEs
contain all the adjacencies of the according node. This will be
necessary for algorithms further elaborated on in Section 4.2.3.9 and
Section 4.3.7.
For node TIEs to carry more adjacencies than fit into an MTU, the
element `neighbors` may contain different set of neighbors in each
TIE. Those disjoint sets of neighbors MUST be joined during
according computation. Nevertheless, in case across multiple node
TIEs
1. `capabilities` do not match *or*
2. `flags` values do not match *or*
3. same neighbor repeats with different values
the behavior is undefined and a warning SHOULD be generated after a
period of time. The element `miscabled_links` SHOULD be repeated in
every node TIE, otherwise the behavior is undefined.
Different TIE types are carried in `TIEElement`. Schema enum
`common.TIETypeType` in `TIEID` indicates which elements MUST be
present in the `TIEElement`. In case of mismatch the unexpected
elements MUST be ignored. In case of lack of expected element in the
TIE an error MUST be reported and the TIE MUST be ignored.
`positive_disaggregation_prefixes` and
`positive_external_disaggregation_prefixes` MUST be advertised
southbound only and ignored in North TIEs.
`negative_disaggregation_prefixes` MUST be aggregated and propagated
according to Section 4.2.5.2 southwards towards lower levels to heal
pathological upper level partitioning, otherwise blackholes may occur
in multiplane fabrics. It MUST NOT be advertised within a North TIE
and ignored otherwise.
4.2.3.3. Flooding
The mechanism used to distribute TIEs is the well-known (albeit
modified in several respects to take advantage of Fat Tree topology)
flooding mechanism used in link-state protocols. Although flooding
is initially more demanding to implement it avoids many problems with
update style used in diffused computation by distance vector
protocols. However, since flooding tends to present a significant
burden in large, densely meshed topologies (Fat Trees being
unfortunately such a topology) RIFT provides as solution a close to
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optimal global flood reduction and load balancing optimization in
Section 4.2.3.9.
As described before, TIEs themselves are transported over UDP with
the ports indicated in the LIE exchanges and using the destination
address on which the LIE adjacency has been formed. For unnumbered
IPv4 interfaces same considerations apply as in other link-state
routing protocols and are largely implementation dependent.
TIEs are uniquely identifed by `TIEID` schema element. `TIEID` space
is a total order achieved by comparing the elements in sequence
defined in the element and comparing each value as an unsigned
integer of according length. They contain a `seq_nr` element to
distinguish newer versions of same TIE. TIEIDs also carry
`origination_time` and `origination_lifetime`. Field
`origination_time` contains the absolute timestamp when the TIE was
generated. Field `origination_lifetime` carries lifetime when the
TIE was generated. Those are normally disregarded during comparison
and carried purely for debugging/security purposes if present. They
may be used for comparison of last resort to differentiate otherwise
equal ties and they can be used on fabrics with synchronized clock to
prevent lifetime modification attacks.
Remaining lifetime counts down to 0 from origination lifetime. TIEs
with lifetimes differing by less than `lifetime_diff2ignore` MUST be
considered EQUAL (if all other fields are equal). This constant MUST
be larger than `purge_lifetime` to avoid retransmissions.
All valid TIE types are defined in `TIETypeType`. This enum indicates
what TIE type the TIE is carrying. In case the value is not known to
the receiver, the TIE MUST be re-flooded. This allows for future
extensions of the protocol within the same major schema with types
opaque to some nodes with some restrictions.
4.2.3.3.1. Normative Flooding Procedures
On reception of a TIE with an undefined level value in the packet
header the node MAY issue a warning and indiscriminately discard the
packet. Such packets can be useful however to establish e.g. via
`instance_name`, `name` and `originator` elements in `LIEPacket`
whether the cabling of the node fulfills expectations, even before
ZTP procedures determine levels across the topology.
This section specifies the precise, normative flooding mechanism and
can be omitted unless the reader is pursuing an implementation of the
protocol or looks for a deep understanding of underlying information
distribution mechanism.
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Flooding Procedures are described in terms of a flooding state of an
adjacency and resulting operations on it driven by packet arrivals.
The FSM itself has basically just a single state and is not well
suited to represent the behavior. An implementation MUST either
implement the given procedures in a verbatim manner or behave on the
wire in the same way as the provided normative procedures of this
paragraph.
RIFT does not specify any kind of flood rate limiting since such
specifications always assume particular points in available
technology speeds and feeds and those points are shifting at faster
and faster rate (speed of light holding for the moment).
To help with adjustement of flooding speeds the encoded packets
provide hints to react accordingly to losses or overruns via
`you_are_sending_too_quickly` in `LIEPacket` and `Packet Number` in
security envelope described in Section 4.4.3. Flooding of all
according topology exchange elements SHOULD be performed at highest
feasible rate whereas the rate of transmission MUST be throttled by
reacting to packet elements and adequate features of the system such
as e.g. queue lengths or congestion indications in the protocol
packets.
A node SHOULD NOT send out any topology information elements if the
adjacency is not in a "ThreeWay" state. No further tightening of
this rule as to e.g. sequence is possible due to possible link
buffering and re-ordering of LIEs and TIEs/TIDEs/TIREs in a real
implementation for e.g. performance purposes.
A node MUST drop any received TIEs/TIDEs/TIREs unless it is in
ThreeWay state.
TIDEs and TIREs MUST NOT be re-flooded the way TIEs of other nodes
MUST be always generated by the node itself and cross only to the
neighboring node.
4.2.3.3.1.1. FloodState Structure per Adjacency
The structure contains conceptually on each adjacency the following
elements. The word collection or queue indicates a set of elements
that can be iterated over:
TIES_TX:
Collection containing all the TIEs to transmit on the adjacency.
TIES_ACK:
Collection containing all the TIEs that have to be acknowledged on
the adjacency.
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TIES_REQ:
Collection containing all the TIE headers that have to be
requested on the adjacency.
TIES_RTX:
Collection containing all TIEs that need retransmission with the
according time to retransmit.
Following words are used for well known elements and procedures
operating on this structure:
TIE:
Describes either a full RIFT TIE or accordingly just the
`TIEHeader` or `TIEID` equivalent as defined in Appendix B.3. The
according meaning is unambiguously contained in the context of
each algorithm.
is_flood_reduced(TIE):
returns whether a TIE can be flood reduced or not.
is_tide_entry_filtered(TIE):
returns whether a header should be propagated in TIDE according to
flooding scopes.
is_request_filtered(TIE):
returns whether a TIE request should be propagated to neighbor or
not according to flooding scopes.
is_flood_filtered(TIE):
returns whether a TIE requested be flooded to neighbor or not
according to flooding scopes.
try_to_transmit_tie(TIE):
A. if not is_flood_filtered(TIE) then
1. remove TIE from TIES_RTX if present
2. if TIE" with same key is found on TIES_ACK then
a. if TIE" is same or newer than TIE do nothing else
b. remove TIE" from TIES_ACK and add TIE to TIES_TX
3. else insert TIE into TIES_TX
ack_tie(TIE):
remove TIE from all collections and then insert TIE into TIES_ACK.
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tie_been_acked(TIE):
remove TIE from all collections.
remove_from_all_queues(TIE):
same as `tie_been_acked`.
request_tie(TIE):
if not is_request_filtered(TIE) then remove_from_all_queues(TIE)
and add to TIES_REQ.
move_to_rtx_list(TIE):
remove TIE from TIES_TX and then add to TIES_RTX using TIE
retransmission interval.
clear_requests(TIEs):
remove all TIEs from TIES_REQ.
bump_own_tie(TIE):
for self-originated TIE originate an empty or re-generate with
version number higher then the one in TIE.
The collection SHOULD be served with the following priorities if the
system cannot process all the collections in real time:
1. Elements on TIES_ACK should be processed with highest priority
2. TIES_TX
3. TIES_REQ and TIES_RTX
4.2.3.3.1.2. TIDEs
`TIEID` and `TIEHeader` space forms a strict total order (modulo
incomparable sequence numbers as explained in Appendix A in the very
unlikely event that can occur if a TIE is "stuck" in a part of a
network while the originator reboots and reissues TIEs many times to
the point its sequence# rolls over and forms incomparable distance to
the "stuck" copy) which implies that a comparison relation is
possible between two elements. With that it is implicitly possible
to compare TIEs, TIEHeaders and TIEIDs to each other whereas the
shortest viable key is always implied.
When generating and sending TIDEs an implementation SHOULD ensure
that enough bandwidth is left to send elements from other queues of
`Floodstate` structure.
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4.2.3.3.1.2.1. TIDE Generation
As given by timer constant, periodically generate TIDEs by:
NEXT_TIDE_ID: ID of next TIE to be sent in TIDE.
TIDE_START: Begin of TIDE packet range.
a. NEXT_TIDE_ID = MIN_TIEID
b. while NEXT_TIDE_ID not equal to MAX_TIEID do
1. TIDE_START = NEXT_TIDE_ID
2. HEADERS = At most TIRDEs_PER_PKT headers in TIEDB starting at
NEXT_TIDE_ID or higher that SHOULD be filtered by
is_tide_entry_filtered and MUST either have a lifetime left >
0 or have no content
3. if HEADERS is empty then START = MIN_TIEID else START = first
element in HEADERS
4. if HEADERS' size less than TIRDEs_PER_PKT then END =
MAX_TIEID else END = last element in HEADERS
5. send *sorted* HEADERS as TIDE setting START and END as its
range
6. NEXT_TIDE_ID = END
The constant `TIRDEs_PER_PKT` SHOULD be computed per interface and
used by the implementation to limit the amount of TIE headers per
TIDE so the sent TIDE PDU does not exceed interface MTU.
TIDE PDUs SHOULD be spaced on sending to prevent packet drops.
4.2.3.3.1.2.2. TIDE Processing
On reception of TIDEs the following processing is performed:
TXKEYS: Collection of TIE Headers to be sent after processing of
the packet
REQKEYS: Collection of TIEIDs to be requested after processing of
the packet
CLEARKEYS: Collection of TIEIDs to be removed from flood state
queues
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LASTPROCESSED: Last processed TIEID in TIDE
DBTIE: TIE in the LSDB if found
a. LASTPROCESSED = TIDE.start_range
b. for every HEADER in TIDE do
1. DBTIE = find HEADER in current LSDB
2. if HEADER < LASTPROCESSED then report error and reset
adjacency and return
3. put all TIEs in LSDB where (TIE.HEADER > LASTPROCESSED and
TIE.HEADER < HEADER) into TXKEYS
4. LASTPROCESSED = HEADER
5. if DBTIE not found then
I) if originator is this node then bump_own_tie
II) else put HEADER into REQKEYS
6. if DBTIE.HEADER < HEADER then
I) if originator is this node then bump_own_tie else
i. if this is a North TIE header from a northbound
neighbor then override DBTIE in LSDB with HEADER
ii. else put HEADER into REQKEYS
7. if DBTIE.HEADER > HEADER then put DBTIE.HEADER into TXKEYS
8. if DBTIE.HEADER = HEADER then
I) if DBTIE has content already then put DBTIE.HEADER into
CLEARKEYS
II) else put HEADER into REQKEYS
c. put all TIEs in LSDB where (TIE.HEADER > LASTPROCESSED and
TIE.HEADER <= TIDE.end_range) into TXKEYS
d. for all TIEs in TXKEYS try_to_transmit_tie(TIE)
e. for all TIEs in REQKEYS request_tie(TIE)
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f. for all TIEs in CLEARKEYS remove_from_all_queues(TIE)
4.2.3.3.1.3. TIREs
4.2.3.3.1.3.1. TIRE Generation
Elements from both TIES_REQ and TIES_ACK MUST be collected and sent
out as fast as feasible as TIREs. When sending TIREs with elements
from TIES_REQ the `remaining_lifetime` field in
`TIEHeaderWithLifeTime` MUST be set to 0 to force reflooding from the
neighbor even if the TIEs seem to be same.
4.2.3.3.1.3.2. TIRE Processing
On reception of TIREs the following processing is performed:
TXKEYS: Collection of TIE Headers to be send after processing of
the packet
REQKEYS: Collection of TIEIDs to be requested after processing of
the packet
ACKKEYS: Collection of TIEIDs that have been acked
DBTIE: TIE in the LSDB if found
a. for every HEADER in TIRE do
1. DBTIE = find HEADER in current LSDB
2. if DBTIE not found then do nothing
3. if DBTIE.HEADER < HEADER then put HEADER into REQKEYS
4. if DBTIE.HEADER > HEADER then put DBTIE.HEADER into TXKEYS
5. if DBTIE.HEADER = HEADER then put DBTIE.HEADER into ACKKEYS
b. for all TIEs in TXKEYS try_to_transmit_tie(TIE)
c. for all TIEs in REQKEYS request_tie(TIE)
d. for all TIEs in ACKKEYS tie_been_acked(TIE)
4.2.3.3.1.4. TIEs Processing on Flood State Adjacency
On reception of TIEs the following processing is performed:
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ACKTIE: TIE to acknowledge
TXTIE: TIE to transmit
DBTIE: TIE in the LSDB if found
a. DBTIE = find TIE in current LSDB
b. if DBTIE not found then
1. if originator is this node then bump_own_tie with a short
remaining lifetime
2. else insert TIE into LSDB and ACKTIE = TIE
else
1. if DBTIE.HEADER = TIE.HEADER then
i. if DBTIE has content already then ACKTIE = TIE
ii. else process like the "DBTIE.HEADER < TIE.HEADER" case
2. if DBTIE.HEADER < TIE.HEADER then
i. if originator is this node then bump_own_tie
ii. else insert TIE into LSDB and ACKTIE = TIE
3. if DBTIE.HEADER > TIE.HEADER then
i. if DBTIE has content already then TXTIE = DBTIE
ii. else ACKTIE = DBTIE
c. if TXTIE is set then try_to_transmit_tie(TXTIE)
d. if ACKTIE is set then ack_tie(TIE)
4.2.3.3.1.5. Sending TIEs
On a periodic basis all TIEs with lifetime left > 0 MUST be sent out
on the adjacency, removed from TIES_TX list and requeued onto
TIES_RTX list.
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4.2.3.3.1.6. TIEs Processing In LSDB
The Link State Database can be considered to be a switchboard that
does not need any flooding procedures but can be given versions of
TIEs by peers. Consecutively, after version tie-breaking by LSDB, a
peer receives from the LSDB newest versions of TIEs received by other
peers and processes them (without any filtering) just like receiving
TIEs from its remote peer. Such a publisher model can be implemented
in many ways, either in a single thread of execution of in parallel
threads.
LSDB can be logically considered as the entity aging out TIEs, i.e.
being responsible to discard TIEs that are stored longer than
`remaining_lifetime` on their reception.
LSDB is also expected to periodically re-originate the node's own
TIEs. It is recommended to originate at interval significantly
shorter than `default_lifetime` to prevent TIE expiration by other
nodes in the network which can lead to instabilities.
4.2.3.4. TIE Flooding Scopes
In a somewhat analogous fashion to link-local, area and domain
flooding scopes, RIFT defines several complex "flooding scopes"
depending on the direction and type of TIE propagated.
Every North TIE is flooded northbound, providing a node at a given
level with the complete topology of the Clos or Fat Tree network that
is reachable southwards of it, including all specific prefixes. This
means that a packet received from a node at the same or lower level
whose destination is covered by one of those specific prefixes will
be routed directly towards the node advertising that prefix rather
than sending the packet to a node at a higher level.
A node's Node South TIEs, consisting of all node's adjacencies and
prefix South TIEs limited to those related to default IP prefix and
disaggregated prefixes, are flooded southbound in order to allow the
nodes one level down to see connectivity of the higher level as well
as reachability to the rest of the fabric. In order to allow an E-W
disconnected node in a given level to receive the South TIEs of other
nodes at its level, every *NODE* South TIE is "reflected" northbound
to level from which it was received. It should be noted that East-
West links are included in South TIE flooding (except at ToF level);
those TIEs need to be flooded to satisfy algorithms in Section 4.2.4.
In that way nodes at same level can learn about each other without a
lower level except in case of leaf level. The precise, normative
flooding scopes are given in Table 3. Those rules govern as well
what SHOULD be included in TIDEs on the adjacency. Again, East-West
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flooding scopes are identical to South flooding scopes except in case
of ToF East-West links (rings) which are basically performing
northbound flooding.
Node South TIE "south reflection" allows to support positive
disaggregation on failures as described in in Section 4.2.5 and
flooding reduction in Section 4.2.3.9.
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+===========+======================+==============+=================+
| Type / | South | North | East-West |
| Direction | | | |
+===========+======================+==============+=================+
| node | flood if level of | flood if | flood only if |
| South TIE | originator is | level of | this node is |
| | equal to this | originator | not ToF |
| | node | is higher | |
| | | than this | |
| | | node | |
+-----------+----------------------+--------------+-----------------+
| non-node | flood self- | flood only | flood only if |
| South TIE | originated only | if neighbor | self-originated |
| | | is | and this node |
| | | originator | is not ToF |
| | | of TIE | |
+-----------+----------------------+--------------+-----------------+
| all North | never flood | flood always | flood only if |
| TIEs | | | this node is |
| | | | ToF |
+-----------+----------------------+--------------+-----------------+
| TIDE | include at least | include at | if this node is |
| | all non-self | least all | ToF then |
| | originated North | node South | include all |
| | TIE headers and | TIEs and all | North TIEs, |
| | self-originated | South TIEs | otherwise only |
| | South TIE headers | originated | self-originated |
| | and node South | by peer and | TIEs |
| | TIEs of nodes at | all North | |
| | same level | TIEs | |
+-----------+----------------------+--------------+-----------------+
| TIRE as | request all North | request all | if this node is |
| Request | TIEs and all | South TIEs | ToF then apply |
| | peer's self- | | North scope |
| | originated TIEs | | rules, |
| | and all node | | otherwise South |
| | South TIEs | | scope rules |
+-----------+----------------------+--------------+-----------------+
| TIRE as | Ack all received | Ack all | Ack all |
| Ack | TIEs | received | received TIEs |
| | | TIEs | |
+-----------+----------------------+--------------+-----------------+
Table 3: Normative Flooding Scopes
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If the TIDE includes additional TIE headers beside the ones
specified, the receiving neighbor must apply according filter to the
received TIDE strictly and MUST NOT request the extra TIE headers
that were not allowed by the flooding scope rules in its direction.
As an example to illustrate these rules, consider using the topology
in Figure 2, with the optional link between spine 111 and spine 112,
and the associated TIEs given in Figure 15. The flooding from
particular nodes of the TIEs is given in Table 4.
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+============+==========+===========================================+
| Local | Neighbor | TIEs Flooded from Local to Neighbor Node |
| Node | Node | |
+============+==========+===========================================+
| Leaf111 | Spine | Leaf111 North TIEs, Spine 111 node South |
| | 112 | TIE |
+------------+----------+-------------------------------------------+
| Leaf111 | Spine | Leaf111 North TIEs, Spine 112 node South |
| | 111 | TIE |
+------------+----------+-------------------------------------------+
| ... | ... | ... |
+------------+----------+-------------------------------------------+
| Spine | Leaf111 | Spine 111 South TIEs |
| 111 | | |
+------------+----------+-------------------------------------------+
| Spine | Leaf112 | Spine 111 South TIEs |
| 111 | | |
+------------+----------+-------------------------------------------+
| Spine | Spine | Spine 111 South TIEs |
| 111 | 112 | |
+------------+----------+-------------------------------------------+
| Spine | ToF 21 | Spine 111 North TIEs, Leaf111 North TIEs, |
| 111 | | Leaf112 North TIEs, ToF 22 node South TIE |
+------------+----------+-------------------------------------------+
| Spine | ToF 22 | Spine 111 North TIEs, Leaf111 North TIEs, |
| 111 | | Leaf112 North TIEs, ToF 21 node South TIE |
+------------+----------+-------------------------------------------+
| ... | ... | ... |
+------------+----------+-------------------------------------------+
| ToF 21 | Spine | ToF 21 South TIEs |
| | 111 | |
+------------+----------+-------------------------------------------+
| ToF 21 | Spine | ToF 21 South TIEs |
| | 112 | |
+------------+----------+-------------------------------------------+
| ToF 21 | Spine | ToF 21 South TIEs |
| | 121 | |
+------------+----------+-------------------------------------------+
| ToF 21 | Spine | ToF 21 South TIEs |
| | 122 | |
+------------+----------+-------------------------------------------+
| ... | ... | ... |
+------------+----------+-------------------------------------------+
Table 4: Flooding some TIEs from example topology
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4.2.3.5. 'Flood Only Node TIEs' Bit
RIFT includes an optional ECN (Explicit Congestion Notification)
mechanism to prevent "flooding inrush" on restart or bring-up with
many southbound neighbors. A node MAY set on its LIEs the according
`you_are_sending_too_quickly` flag to indicate to the neighbor that
it should temporarily flood node TIEs only to it and slow down the
flooding of any other TIEs. It SHOULD only set it in the southbound
direction. The receiving node SHOULD accommodate the request to
lessen the flooding load on the affected node if south of the sender
and SHOULD ignore the indication if northbound.
Obviously this mechanism is most useful in the southbound direction.
The distribution of node TIEs guarantees correct behavior of
algorithms like disaggregation or default route origination.
Furthermore though, the use of this bit presents an inherent trade-
off between processing load and convergence speed since suppressing
flooding of northbound prefixes from neighbors permanently will lead
to blackholes.
4.2.3.6. Initial and Periodic Database Synchronization
The initial exchange of RIFT includes periodic TIDE exchanges that
contain description of the link state database and TIREs which
perform the function of requesting unknown TIEs as well as confirming
reception of flooded TIEs. The content of TIDEs and TIREs is
governed by Table 3.
4.2.3.7. Purging and Roll-Overs
When a node exits the network, if "unpurged", residual stale TIEs may
exist in the network until their lifetimes expire (which in case of
RIFT is by default a rather long period to prevent ongoing re-
origination of TIEs in very large topologies). RIFT does however not
have a "purging mechanism" in the traditional sense based on sending
specialized "purge" packets. In other routing protocols such
mechanism has proven to be complex and fragile based on many years of
experience. RIFT simply issues a new, i.e. higher sequence number,
empty version of the TIE with a short lifetime given by
`purge_lifetime` constant and relies on each node to age out and
delete such TIE copy independently. Abundant amounts of memory are
available today even on low-end platforms and hence keeping those
relatively short-lived extra copies for a while is acceptable. The
information will age out and in the meantime all computations will
deliver correct results if a node leaves the network due to the new
information distributed by its adjacent nodes breaking bi-directional
connectivity checks in different computations.
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Once a RIFT node issues a TIE with an ID, it SHOULD preserve the ID
as long as feasible (also when the protocol restarts), even if the
TIE looses all content. The re-advertisement of empty TIE fulfills
the purpose of purging any information advertised in previous
versions. The originator is free to not re-originate the according
empty TIE again or originate an empty TIE with relatively short
lifetime to prevent large number of long-lived empty stubs polluting
the network. Each node MUST timeout and clean up the according empty
TIEs independently.
Upon restart a node MUST, as any link-state implementation, be
prepared to receive TIEs with its own system ID and supersede them
with equivalent, newly generated, empty TIEs with a higher sequence
number. As above, the lifetime can be relatively short since it only
needs to exceed the necessary propagation and processing delay by all
the nodes that are within the TIE's flooding scope.
TIE sequence numbers are rolled over using the method described in
Appendix A. First sequence number of any spontaneously originated
TIE (i.e. not originated to override a detected older copy in the
network) MUST be a reasonably unpredictable random number in the
interval [0, 2^30-1] which will prevent otherwise identical TIE
headers to remain "stuck" in the network with content different from
TIE originated after reboot. In traditional link-state protocols
this is delegated to a 16-bit checksum on packet content. RIFT
avoids this design due to the CPU burden presented by computation of
such checksums and additional complications tied to the fact that the
checksum must be "patched" into the packet after the generation of
the content, a difficult proposition in binary hand-crafted formats
already and highly incompatible with model-based, serialized formats.
The sequence number space is hence consciously chosen to be 64-bits
wide to make the occurrence of a TIE with same sequence number but
different content as much or even more unlikely than the checksum
method. To emulate the "checksum behavior" an implementation could
e.g. choose to compute 64-bit checksum over the TIE content and use
that as part of the first sequence number after reboot.
4.2.3.8. Southbound Default Route Origination
Under certain conditions nodes issue a default route in their South
Prefix TIEs with costs as computed in Section 4.3.7.1.
A node X that
1. is *not* overloaded *and*
2. has southbound or East-West adjacencies
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SHOULD originate in its south prefix TIE such a default route if and
only if
1. all other nodes at X's' level are overloaded *or*
2. all other nodes at X's' level have NO northbound adjacencies *or*
3. X has computed reachability to a default route during N-SPF.
The term "all other nodes at X's' level" describes obviously just the
nodes at the same level in the PoD with a viable lower level
(otherwise the node South TIEs cannot be reflected and the nodes in
e.g. PoD 1 and PoD 2 are "invisible" to each other).
A node originating a southbound default route SHOULD install a
default discard route if it did not compute a default route during
N-SPF. This makes the top of the fabric basically a blackhole for
unreachable addresses.
4.2.3.9. Northbound TIE Flooding Reduction
RIFT chooses only a subset of northbound nodes to propagate flooding
and with that both balances it (to prevent 'hot' flooding links)
across the fabric as well as reduces its volume. The solution is
based on several principles:
1. a node MUST flood self-originated North TIEs to all the reachable
nodes at the level above which is called the node's "parents";
2. it is typically not necessary that all parents reflood the North
TIEs to achieve a complete flooding of all the reachable nodes
two levels above which we choose to call the node's
"grandparents";
3. to control the volume of its flooding two hops North and yet keep
it robust enough, it is advantageous for a node to select a
subset of its parents as "Flood Repeaters" (FRs), which combined
together deliver two or more copies of its flooding to all of its
parents, i.e. the originating node's grandparents;
4. nodes at the same level do *not* have to agree on a specific
algorithm to select the FRs, but overall load balancing should be
achieved so that different nodes at the same level should tend to
select different parents as FRs;
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5. there are usually many solutions to the problem of finding a set
of FRs for a given node; the problem of finding the minimal set
is (similar to) a NP-Complete problem and a globally optimal set
may not be the minimal one if load-balancing with other nodes is
an important consideration;
6. it is expected that there will be often sets of equivalent nodes
at a level L, defined as having a common set of parents at L+1.
Applying this observation at both L and L+1, an algorithm may
attempt to split the larger problem in a sum of smaller separate
problems;
7. it is another expectation that there will be from time to time a
broken link between a parent and a grandparent, and in that case
the parent is probably a poor FR due to its lower reliability.
An algorithm may attempt to eliminate parents with broken
northbound adjacencies first in order to reduce the number of
FRs. Albeit it could be argued that relying on higher fanout FRs
will slow flooding due to higher replication load reliability of
FR's links seems to be a more pressing concern.
In a fully connected Clos Network, this means that a node selects one
arbitrary parent as FR and then a second one for redundancy. The
computation can be kept relatively simple and completely distributed
without any need for synchronization amongst nodes. In a "PoD"
structure, where the Level L+2 is partitioned in silos of equivalent
grandparents that are only reachable from respective parents, this
means treating each silo as a fully connected Clos Network and solve
the problem within the silo.
In terms of signaling, a node has enough information to select its
set of FRs; this information is derived from the node's parents' Node
South TIEs, which indicate the parent's reachable northbound
adjacencies to its own parents, i.e. the node's grandparents. A node
may send a LIE to a northbound neighbor with the optional boolean
field `you_are_flood_repeater` set to false, to indicate that the
northbound neighbor is not a flood repeater for the node that sent
the LIE. In that case the northbound neighbor SHOULD NOT reflood
northbound TIEs received from the node that sent the LIE. If the
`you_are_flood_repeater` is absent or if `you_are_flood_repeater` is
set to true, then the northbound neighbor is a flood repeater for the
node that sent the LIE and MUST reflood northbound TIEs received from
that node. The element `you_are_flood_repeater` MUST be ignored if
received from a northbound adjacency.
This specification provides a simple default algorithm that SHOULD be
implemented and used by default on every RIFT node.
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* let |NA(Node) be the set of Northbound adjacencies of node Node
and CN(Node) be the cardinality of |NA(Node);
* let |SA(Node) be the set of Southbound adjacencies of node Node
and CS(Node) be the cardinality of |SA(Node);
* let |P(Node) be the set of node Node's parents;
* let |G(Node) be the set of node Node's grandparents. Observe
that |G(Node) = |P(|P(Node));
* let N be the child node at level L computing a set of FR;
* let P be a node at level L+1 and a parent node of N, i.e. bi-
directionally reachable over adjacency ADJ(N, P);
* let G be a grandparent node of N, reachable transitively via a
parent P over adjacencies ADJ(N, P) and ADJ(P, G). Observe that N
does not have enough information to check bidirectional
reachability of ADJ(P, G);
* let R be a redundancy constant integer; a value of 2 or higher for
R is RECOMMENDED;
* let S be a similarity constant integer; a value in range 0 .. 2
for S is RECOMMENDED, the value of 1 SHOULD be used. Two
cardinalities are considered as equivalent if their absolute
difference is less than or equal to S, i.e. |a-b|<=S.
* let RND be a 64-bit random number generated by the system once on
startup.
The algorithm consists of the following steps:
1. Derive a 64-bits number by XOR'ing 'N's system ID with RND.
2. Derive a 16-bits pseudo-random unsigned integer PR(N) from the
resulting 64-bits number by splitting it in 16-bits-long words
W1, W2, W3, W4 (where W1 are the least significant 16 bits of the
64-bits number, and W4 are the most significant 16 bits) and then
XOR'ing the circularly shifted resulting words together:
A. (W1<<1) xor (W2<<2) xor (W3<<3) xor (W4<<4);
where << is the circular shift operator.
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3. Sort the parents by decreasing number of northbound adjacencies
(using decreasing system id of the parent as tie-breaker):
sort |P(N) by decreasing CN(P), for all P in |P(N), as ordered
array |A(N)
4. Partition |A(N) in subarrays |A_k(N) of parents with equivalent
cardinality of northbound adjacencies (in other words with
equivalent number of grandparents they can reach):
A. set k=0; // k is the ID of the subarrray
B. set i=0;
C. while i < CN(N) do
i) set j=i;
ii) while i < CN(N) and CN(|A(N)[j]) - CN(|A(N)[i]) <= S
a. place |A(N)[i] in |A_k(N) // abstract action, maybe
noop
b. set i=i+1;
iii) /* At this point j is the index in |A(N) of the first
member of |A_k(N) and (i-j) is C_k(N) defined as the
cardinality of |A_k(N) */
set k=k+1;
/* At this point k is the total number of subarrays, initialized
for the shuffling operation below */
5. shuffle individually each subarrays |A_k(N) of cardinality C_k(N)
within |A(N) using the Durstenfeld variation of Fisher-Yates
algorithm that depends on N's System ID:
A. while k > 0 do
i) for i from C_k(N)-1 to 1 decrementing by 1 do
a. set j to PR(N) modulo i;
b. exchange |A_k[j] and |A_k[i];
ii) set k=k-1;
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6. For each grandparent G, initialize a counter c(G) with the number
of its south-bound adjacencies to elected flood repeaters (which
is initially zero):
A. for each G in |G(N) set c(G) = 0;
7. Finally keep as FRs only parents that are needed to maintain the
number of adjacencies between the FRs and any grandparent G equal
or above the redundancy constant R:
A. for each P in reshuffled |A(N);
i) if there exists an adjacency ADJ(P, G) in |NA(P) such
that c(G) < R then
a. place P in FR set;
b. for all adjacencies ADJ(P, G') in |NA(P) increment
c(G')
B. If any c(G) is still < R, it was not possible to elect a set
of FRs that covers all grandparents with redundancy R
Additional rules for flooding reduction:
1. The algorithm MUST be re-evaluated by a node on every change of
local adjacencies or reception of a parent South TIE with changed
adjacencies. A node MAY apply a hysteresis to prevent excessive
amount of computation during periods of network instability just
like in case of reachability computation.
2. Upon a change of the flood repeater set, a node SHOULD send out
LIEs that grant flood repeater status to newly promoted nodes
before it sends LIEs that revoke the status to the nodes that
have been newly demoted. This is done to prevent transient
behavior where the full coverage of grandparents is not
guaranteed. Such a condition is sometimes unavoidable in case of
lost LIEs but it will correct itself though at possible transient
hit in flooding propagation speeds. The election can use the LIE
FSM `FloodLeadersChanged` event to notify LIE FSMs of necessity
to update the sent LIEs.
3. A node MUST always flood its self-originated TIEs to all its
neighbors.
4. A node receiving a TIE originated by a node for which it is not a
flood repeater SHOULD NOT reflood such TIEs to its neighbors
except for rules in Section 4.2.3.9, Paragraph 10, Item 6.
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5. The indication of flood reduction capability MUST be carried in
the node TIEs in the `flood_reduction` element and MAY be used to
optimize the algorithm to account for nodes that will flood
regardless.
6. A node generates TIDEs as usual but when receiving TIREs or TIDEs
resulting in requests for a TIE of which the newest received copy
came on an adjacency where the node was not flood repeater it
SHOULD ignore such requests on first and only first request.
Normally, the nodes that received the TIEs as flooding repeaters
should satisfy the requesting node and with that no further TIREs
for such TIEs will be generated. Otherwise, the next set of
TIDEs and TIREs MUST lead to flooding independent of the flood
repeater status. This solves a very difficult incast problem on
nodes restarting with a very wide fanout, especially northbound.
To retrieve the full database they often end up processing many
in-rushing copies whereas this approach load-balances the
incoming database between adjacent nodes and flood repeaters
should guarantee that two copies are sent by different nodes to
ensure against any losses.
4.2.3.10. Special Considerations
First, due to the distributed, asynchronous nature of ZTP, it can
create temporary convergence anomalies where nodes at higher levels
of the fabric temporarily see themselves lower than where they
ultimately belong. Since flooding can begin before ZTP is "finished"
and in fact must do so given there is no global termination criteria
for the unsychronized ZTP algorithm, information may end up
temporarily in wrong layers. A special clause when changing level
takes care of that.
More difficult is a condition where a node (e.g. a leaf) floods a TIE
north towards its grandparent, then its parent reboots, in fact
partitioning the grandparent from leaf directly and then the leaf
itself reboots. That can leave the grandparent holding the "primary
copy" of the leaf's TIE. Normally this condition is resolved easily
by the leaf re-originating its TIE with a higher sequence number than
it sees in the northbound TIEs, here however, when the parent comes
back it won't be able to obtain leaf's North TIE from the grandparent
easily and with that the leaf may not issue the TIE with a higher
sequence number that can reach the grandparent for a long time.
Flooding procedures are extended to deal with the problem by the
means of special clauses that override the database of a lower level
with headers of newer TIEs seen in TIDEs coming from the north.
Those headers are then propagated southbound towards the leaf nudging
it to originate a higher sequence number of the TIE effectively
refreshing it all the way up to ToF.
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4.2.4. Reachability Computation
A node has three possible sources of relevant information for
reachability computation. A node knows the full topology south of it
from the received North Node TIEs or alternately north of it from the
South Node TIEs. A node has the set of prefixes with their
associated distances and bandwidths from corresponding prefix TIEs.
To compute prefix reachability, a node runs conceptually a northbound
and a southbound SPF. N-SPF and S-SPF notation denotes here the
direction in which the computation front is progressing.
Since neither computation can "loop", it is possible to compute non-
equal-cost or even k-shortest paths [EPPSTEIN] and "saturate" the
fabric to the extent desired. This specification however uses
simple, familiar SPF algorithms and concepts as example due to their
prevalence in today's routing.
For reachability computation purposes RIFT considers all parallel
links between two nodes to be of the same cost advertised in `cost`
element of `NodeNeighborsTIEElement`. In case the neighbor has
multiple parallel links at different cost, the largest distance
(highest numerical value) MUST be advertised. Given the range of
thrift encodings, `infinite_distance` is defined as largest non-
negative `MetricType`. Any link with metric larger than that (i.e.
negative MetricType) MUST be ignored in computations. Any link with
metric set to `invalid_distance` MUST be ignored in computation as
well. In case of a negatively distributed prefix the metric
attribute MUST be set to `infinite_distance` by the originator and it
MUST be ignored by all nodes during computation except for the
purpose of determining transitive propagation and building the
according routing table.
A prefix can carry the `directly_attached` attribute to indicate that
the prefix is directly attached, i.e. should be routed to even if the
node is in overload. In case of a negatively distributed prefix this
attribute MUST not be included by the originator and it MUST be
ignored by all nodes during SPF computation. If a prefix is locally
originated the attribute `from_link` can indicate the interface to
which the address belongs to. In case of a negatively distributed
prefix this attribute MUST NOT be included by the originator and it
MUST be ignored by all nodes during computation. A prefix can also
carry the `loopback` attribute to indicate the said property.
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Prefixes are carried in different type of TIEs indicating their type.
For same prefix being included in different TIE types according to
Section 4.3.1. In case the same prefix is included multiple times in
multiple TIEs of same type originating at the same node the resulting
behavior is unspecified.
4.2.4.1. Northbound Reachability SPF
N-SPF MUST use exclusively northbound and East-West adjacencies in
the computing node's node North TIEs (since if the node is a leaf it
may not have generated a node South TIE) when starting SPF. Observe
that N-SPF is really just a one hop variety since Node South TIEs are
not re-flooded southbound beyond a single level (or East-West) and
with that the computation cannot progress beyond adjacent nodes.
Once progressing, the computation uses the next higher level's node
South TIEs to find according adjacencies to verify backlink
connectivity. Two unidirectional links MUST be associated together
to confirm bidirectional connectivity, a process often known as
`backlink check`. As part of the check, both node TIEs MUST contain
the correct system IDs *and* expected levels.
Default route found when crossing an E-W link SHOULD be used if and
only if
1. the node itself does *not* have any northbound adjacencies *and*
2. the adjacent node has one or more northbound adjacencies
This rule forms a "one-hop default route split-horizon" and prevents
looping over default routes while allowing for "one-hop protection"
of nodes that lost all northbound adjacencies except at Top-of-Fabric
where the links are used exclusively to flood topology information in
multi-plane designs.
Other south prefixes found when crossing E-W link MAY be used if and
only if
1. no north neighbors are advertising same or supersuming non-
default prefix *and*
2. the node does not originate a non-default supersuming prefix
itself.
i.e. the E-W link can be used as a gateway of last resort for a
specific prefix only. Using south prefixes across E-W link can be
beneficial e.g. on automatic disaggregation in pathological fabric
partitioning scenarios.
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A detailed example can be found in Section 5.4.
4.2.4.2. Southbound Reachability SPF
S-SPF MUST use the southbound adjacencies in the node South TIEs
exclusively, i.e. progresses towards nodes at lower levels. Observe
that E-W adjacencies are NEVER used in this computation. This
enforces the requirement that a packet traversing in a southbound
direction must never change its direction.
S-SPF MUST use northbound adjacencies in node North TIEs to verify
backlink connectivity by checking for presence of the link beside
correct System ID and level.
4.2.4.3. East-West Forwarding Within a non-ToF Level
Using south prefixes over horizontal links MAY occur if the N-SPF
includes East-West adjacencies in computation. It can protect
against pathological fabric partitioning cases that leave only paths
to destinations that would necessitate multiple changes of forwarding
direction between north and south.
4.2.4.4. East-West Links Within ToF Level
E-W ToF links behave in terms of flooding scopes defined in
Section 4.2.3.4 like northbound links and MUST be used exclusively
for control plane information flooding. Even though a ToF node could
be tempted to use those links during southbound SPF and carry traffic
over them this MUST NOT be attempted since it may lead in, e.g.
anycast cases to routing loops. An implementation MAY try to resolve
the looping problem by following on the ring strictly tie-broken
shortest-paths only but the details are outside this specification.
And even then, the problem of proper capacity provisioning of such
links when they become traffic-bearing in case of failures is vexing
and when used for forwarding purposes, they defeat statistical non-
blocking guarantees that Clos is providing normally.
4.2.5. Automatic Disaggregation on Link & Node Failures
4.2.5.1. Positive, Non-transitive Disaggregation
Under normal circumstances, a node's South TIEs contain just the
adjacencies and a default route. However, if a node detects that its
default IP prefix covers one or more prefixes that are reachable
through it but not through one or more other nodes at the same level,
then it MUST explicitly advertise those prefixes in an South TIE.
Otherwise, some percentage of the northbound traffic for those
prefixes would be sent to nodes without according reachability,
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causing it to be black-holed. Even when not black-holing, the
resulting forwarding could 'backhaul' packets through the higher
level spines, clearly an undesirable condition affecting the blocking
probabilities of the fabric.
This specification refers to the process of advertising additional
prefixes southbound as 'positive disaggregation'. Such
disaggregation is non-transitive, i.e. its' effects are always
contained to a single level of the fabric only. Naturally, multiple
node or link failures can lead to several independent instances of
positive disaggregation necessary to prevent looping or bow-tying the
fabric.
A node determines the set of prefixes needing disaggregation using
the following steps:
1. A DAG computation in the southern direction is performed first,
i.e. the North TIEs are used to find all of prefixes it can reach
and the set of next-hops in the lower level for each of them.
Such a computation can be easily performed on a Fat Tree by e.g.
setting all link costs in the southern direction to 1 and all
northern directions to infinity. We term set of those
prefixes |R, and for each prefix, r, in |R, its set of next-hops
is defined to be |H(r).
2. The node uses reflected South TIEs to find all nodes at the same
level in the same PoD and the set of southbound adjacencies for
each. The set of nodes at the same level is termed |N and for
each node, n, in |N, its set of southbound adjacencies is defined
to be |A(n).
3. For a given r, if the intersection of |H(r) and |A(n), for any n,
is empty then that prefix r must be explicitly advertised by the
node in an South TIE.
4. Identical set of disaggregated prefixes is flooded on each of the
node's southbound adjacencies. In accordance with the normal
flooding rules for an South TIE, a node at the lower level that
receives this South TIE SHOULD NOT propagate it south-bound or
reflect the disaggregated prefixes back over its adjacencies to
nodes at the level from which it was received.
To summarize the above in simplest terms: if a node detects that its
default route encompasses prefixes for which one of the other nodes
in its level has no possible next-hops in the level below, it has to
disaggregate it to prevent black-holing or suboptimal routing through
such nodes. Hence a node X needs to determine if it can reach a
different set of south neighbors than other nodes at the same level,
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which are connected to it via at least one common south neighbor. If
it can, then prefix disaggregation may be required. If it can't,
then no prefix disaggregation is needed. An example of
disaggregation is provided in Section 5.3.
Finally, a possible algorithm is described here:
1. Create partial_neighbors = (empty), a set of neighbors with
partial connectivity to the node X's level from X's perspective.
Each entry in the set is a south neighbor of X and a list of
nodes of X.level that can't reach that neighbor.
2. A node X determines its set of southbound neighbors
X.south_neighbors.
3. For each South TIE originated from a node Y that X has which is
at X.level, if Y.south_neighbors is not the same as
X.south_neighbors but the nodes share at least one southern
neighbor, for each neighbor N in X.south_neighbors but not in
Y.south_neighbors, add (N, (Y)) to partial_neighbors if N isn't
there or add Y to the list for N.
4. If partial_neighbors is empty, then node X does not disaggregate
any prefixes. If node X is advertising disaggregated prefixes in
its South TIE, X SHOULD remove them and re-advertise its
according South TIEs.
A node X computes reachability to all nodes below it based upon the
received North TIEs first. This results in a set of routes, each
categorized by (prefix, path_distance, next-hop set). Alternately,
for clarity in the following procedure, these can be organized by
next-hop set as ((next-hops), {(prefix, path_distance)}). If
partial_neighbors isn't empty, then the following procedure describes
how to identify prefixes to disaggregate.
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disaggregated_prefixes = { empty }
nodes_same_level = { empty }
for each South TIE
if (South TIE.level == X.level and
X shares at least one S-neighbor with X)
add South TIE.originator to nodes_same_level
end if
end for
for each next-hop-set NHS
isolated_nodes = nodes_same_level
for each NH in NHS
if NH in partial_neighbors
isolated_nodes =
intersection(isolated_nodes,
partial_neighbors[NH].nodes)
end if
end for
if isolated_nodes is not empty
for each prefix using NHS
add (prefix, distance) to disaggregated_prefixes
end for
end if
end for
copy disaggregated_prefixes to X's South TIE
if X's South TIE is different
schedule South TIE for flooding
end if
Figure 16: Computation of Disaggregated Prefixes
Each disaggregated prefix is sent with the according path_distance.
This allows a node to send the same South TIE to each south neighbor.
The south neighbor which is connected to that prefix will thus have a
shorter path.
Finally, to summarize the less obvious points partially omitted in
the algorithms to keep them more tractable:
1. all neighbor relationships MUST perform backlink checks.
2. overload bits as introduced in Section 4.3.2 and carried in
`overload` schema element have to be respected during the
computation, i.e. node advertising themselves as overloaded MUST
NOT be transited in reachability computation but MUST be used as
terminal nodes with prefixes they advertise being reachable.
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3. all the lower level nodes are flooded the same disaggregated
prefixes since RIFT does not build an South TIE per node which
would complicate things unnecessarily. The lower level node that
can compute a southbound route to the prefix will prefer it to
the disaggregated route anyway based on route preference rules.
4. positively disaggregated prefixes do *not* have to propagate to
lower levels. With that the disturbance in terms of new flooding
is contained to a single level experiencing failures.
5. disaggregated Prefix South TIEs are not "reflected" by the lower
level, i.e. nodes within same level do *not* need to be aware
which node computed the need for disaggregation.
6. The fabric is still supporting maximum load balancing properties
while not trying to send traffic northbound unless necessary.
In case positive disaggregation is triggered and due to the very
stable but un-synchronized nature of the algorithm the nodes may
issue the necessary disaggregated prefixes at different points in
time. This can lead for a short time to an "incast" behavior where
the first advertising router based on the nature of longest prefix
match will attract all the traffic. Different implementation
strategies can be used to lessen that effect but those are clearly
outside the scope of this specification.
To close this section it is worth to observe that in a single plane
ToF this disaggregation prevents blackholing up to (K_LEAF * P) link
failures in terms of Section 4.1.2 or in other terms, it takes at
minimum that many link failures to partition the ToF into multiple
planes.
4.2.5.2. Negative, Transitive Disaggregation for Fallen Leaves
As explained in Section 4.1.3 failures in multi-plane Top-of-Fabric
or more than (K_LEAF * P) links failing in single plane design can
generate fallen leaves. Such scenario cannot be addressed by
positive disaggregation only and needs a further mechanism.
4.2.5.2.1. Cabling of Multiple Top-of-Fabric Planes
Returning in this section to designs with multiple planes as shown
originally in Figure 3, Figure 17 highlights now how the ToF is
cabled in case of two planes by the means of dual-rings to distribute
all the North TIEs within both planes.
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++==========++ ++==========++
II II II II
+----++--+ +----++--+ +----++--+ +----++--+
|ToF A1| |ToF B1| |ToF B2| |ToF A2|
++-+-++--+ ++-+-++--+ ++-+-++--+ ++-+-++--+
| | II | | II | | II | | II
| | ++==========++ | | ++==========++
| | | | | | | |
~~~ Highlighted ToF of the previous multi-plane figure ~~
Figure 17: Topologically Connected Planes
Section 4.1.3 already describes how failures in multi-plane fabrics
can lead to blackholes which normal positive disaggregation cannot
fix. The mechanism of negative, transitive disaggregation
incorporated in RIFT provides the according solution and next section
explains the involved mechanisms in more detail.
4.2.5.2.2. Transitive Advertisement of Negative Disaggregates
A ToF node discovering that it cannot reach a fallen leaf SHOULD
disaggregate all the prefixes of such leaves. It uses for that
purpose negative prefix South TIEs that are, as usual, flooded
southwards with the scope defined in Section 4.2.3.4.
Transitively, a node explicitly loses connectivity to a prefix when
none of its children advertises it and when the prefix is negatively
disaggregated by all of its parents. When that happens, the node
originates the negative prefix further down south. Since the
mechanism applies recursively south the negative prefix may propagate
transitively all the way down to the leaf. This is necessary since
leaves connected to multiple planes by means of disjoint paths may
have to choose the correct plane already at the very bottom of the
fabric to make sure that they don't send traffic towards another leaf
using a plane where it is "fallen" at which in point a blackhole is
unavoidable.
When the connectivity is restored, a node that disaggregated a prefix
withdraws the negative disaggregation by the usual mechanism of re-
advertising TIEs omitting the negative prefix.
4.2.5.2.3. Computation of Negative Disaggregates
The document omitted so far the description of the computation
necessary to generate the correct set of negative prefixes. Negative
prefixes can in fact be advertised due to two different triggers.
This will be described consecutively.
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The first origination reason is a computation that uses all the node
North TIEs to build the set of all reachable nodes by reachability
computation over the complete graph and including horizontal ToF
links. The computation uses the node itself as root. This is
compared with the result of the normal southbound SPF as described in
Section 4.2.4.2. The difference are the fallen leaves and all their
attached prefixes are advertised as negative prefixes southbound if
the node does not see the prefix being reachable within the
southbound SPF.
The second mechanism hinges on the understanding how the negative
prefixes are used within the computation as described in Figure 18.
When attaching the negative prefixes at certain point in time the
negative prefix may find itself with all the viable nodes from the
shorter match nexthop being pruned. In other words, all its
northbound neighbors provided a negative prefix advertisement. This
is the trigger to advertise this negative prefix transitively south
and normally caused by the node being in a plane where the prefix
belongs to a fabric leaf that has "fallen" in this plane. Obviously,
when one of the northbound switches withdraws its negative
advertisement, the node has to withdraw its transitively provided
negative prefix as well.
4.2.6. Attaching Prefixes
After SPF is run, it is necessary to attach the resulting
reachability information in form of prefixes. For S-SPF, prefixes
from an North TIE are attached to the originating node with that
node's next-hop set and a distance equal to the prefix's cost plus
the node's minimized path distance. The RIFT route database, a set
of (prefix, prefix-type, attributes, path_distance, next-hop set),
accumulates these results.
In case of N-SPF prefixes from each South TIE need to also be added
to the RIFT route database. The N-SPF is really just a stub so the
computing node needs simply to determine, for each prefix in an South
TIE that originated from adjacent node, what next-hops to use to
reach that node. Since there may be parallel links, the next-hops to
use can be a set; presence of the computing node in the associated
Node South TIE is sufficient to verify that at least one link has
bidirectional connectivity. The set of minimum cost next-hops from
the computing node X to the originating adjacent node is determined.
Each prefix has its cost adjusted before being added into the RIFT
route database. The cost of the prefix is set to the cost received
plus the cost of the minimum distance next-hop to that neighbor while
taking into account its attributes such as mobility per
Section 4.3.4. Then each prefix can be added into the RIFT route
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database with the next-hop set; ties are broken based upon type first
and then distance and further on `PrefixAttributes` and only the best
combination is used for forwarding. RIFT route preferences are
normalized by the according Thrift [thrift] model type.
An example implementation for node X follows:
for each South TIE
if South TIE.level > X.level
next_hop_set = set of minimum cost links to the
South TIE.originator
next_hop_cost = minimum cost link to
South TIE.originator
end if
for each prefix P in the South TIE
P.cost = P.cost + next_hop_cost
if P not in route_database:
add (P, P.cost, P.type,
P.attributes, next_hop_set) to route_database
end if
if (P in route_database):
if route_database[P].cost > P.cost or
route_database[P].type > P.type:
update route_database[P] with (P, P.type, P.cost,
P.attributes,
next_hop_set)
else if route_database[P].cost == P.cost and
route_database[P].type == P.type:
update route_database[P] with (P, P.type,
P.cost, P.attributes,
merge(next_hop_set, route_database[P].next_hop_set))
else
// Not preferred route so ignore
end if
end if
end for
end for
Figure 18: Adding Routes from South TIE Positive and Negative
Prefixes
After the positive prefixes are attached and tie-broken, negative
prefixes are attached and used in case of northbound computation,
ideally from the shortest length to the longest. The nexthop
adjacencies for a negative prefix are inherited from the longest
positive prefix that aggregates it, and subsequently adjacencies to
nodes that advertised negative for this prefix are removed.
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The rule of inheritance MUST be maintained when the nexthop list for
a prefix is modified, as the modification may affect the entries for
matching negative prefixes of immediate longer prefix length. For
instance, if a nexthop is added, then by inheritance it must be added
to all the negative routes of immediate longer prefixes length unless
it is pruned due to a negative advertisement for the same next hop.
Similarly, if a nexthop is deleted for a given prefix, then it is
deleted for all the immediately aggregated negative routes. This
will recurse in the case of nested negative prefix aggregations.
The rule of inheritance must also be maintained when a new prefix of
intermediate length is inserted, or when the immediately aggregating
prefix is deleted from the routing table, making an even shorter
aggregating prefix the one from which the negative routes now inherit
their adjacencies. As the aggregating prefix changes, all the
negative routes must be recomputed, and then again the process may
recurse in case of nested negative prefix aggregations.
Although these operations can be computationally expensive, the
overall load on devices in the network is low because these
computations are not run very often, as positive route advertisements
are always preferred over negative ones. This prevents recursion in
most cases because positive reachability information never inherits
next hops.
To make the negative disaggregation less abstract and provide an
example ToP node T1 with 4 ToF parents S1..S4 as represented in
Figure 19 are considered further:
+----+ +----+ +----+ +----+ N
| S1 | | S2 | | S3 | | S4 | ^
+----+ +----+ +----+ +----+ W< + >E
| | | | v
|+--------+ | | S
||+-----------------+ |
|||+----------------+---------+
||||
+----+
| T1 |
+----+
Figure 19: A ToP Node with 4 Parents
If all ToF nodes can reach all the prefixes in the network; with
RIFT, they will normally advertise a default route south. An
abstract Routing Information Base (RIB), more commonly known as a
routing table, stores all types of maintained routes including the
negative ones and "tie-breaks" for the best one, whereas an abstract
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Forwarding table (FIB) retains only the ultimately computed
"positive" routing instructions. In T1, those tables would look as
illustrated in Figure 20:
+---------+
| Default |
+---------+
|
| +--------+
+---> | Via S1 |
| +--------+
|
| +--------+
+---> | Via S2 |
| +--------+
|
| +--------+
+---> | Via S3 |
| +---------+
|
| +--------+
+---> | Via S4 |
+--------+
Figure 20: Abstract RIB
In case T1 receives a negative advertisement for prefix 2001:db8::/32
from S1 a negative route is stored in the RIB (indicated by a ~
sign), while the more specific routes to the complementing ToF nodes
are installed in FIB. RIB and FIB in T1 now look as illustrated in
Figure 21 and Figure 22, respectively:
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+---------+ +-----------------+
| Default | <-------------- | ~2001:db8::/32 |
+---------+ +-----------------+
| |
| +--------+ | +--------+
+---> | Via S1 | +---> | Via S1 |
| +--------+ +--------+
|
| +--------+
+---> | Via S2 |
| +--------+
|
| +--------+
+---> | Via S3 |
| +---------+
|
| +--------+
+---> | Via S4 |
+--------+
Figure 21: Abstract RIB after Negative 2001:db8::/32 from S1
The negative 2001:db8::/32 prefix entry inherits from ::/0, so the
positive more specific routes are the complements to S1 in the set of
next-hops for the default route. That entry is composed of S2, S3,
and S4, or, in other words, it uses all entries the the default route
with a "hole punched" for S1 into them. These are the next hops that
are still available to reach 2001:db8::/32, now that S1 advertised
that it will not forward 2001:db8::/32 anymore. Ultimately, those
resulting next-hops are installed in FIB for the more specific route
to 2001:db8::/32 as illustrated below:
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+---------+ +---------------+
| Default | | 2001:db8::/32 |
+---------+ +---------------+
| |
| +--------+ |
+---> | Via S1 | |
| +--------+ |
| |
| +--------+ | +--------+
+---> | Via S2 | +---> | Via S2 |
| +--------+ | +--------+
| |
| +--------+ | +--------+
+---> | Via S3 | +---> | Via S3 |
| +--------+ | +--------+
| |
| +--------+ | +--------+
+---> | Via S4 | +---> | Via S4 |
+--------+ +--------+
Figure 22: Abstract FIB after Negative 2001:db8::/32 from S1
To illustrate matters further consider T1 receiving a negative
advertisement for prefix 2001:db8:1::/48 from S2, which is stored in
RIB again. After the update, the RIB in T1 is illustrated in
Figure 23:
+---------+ +----------------+ +------------------+
| Default | <----- | ~2001:db8::/32 | <------ | ~2001:db8:1::/48 |
+---------+ +----------------+ +------------------+
| | |
| +--------+ | +--------+ |
+---> | Via S1 | +---> | Via S1 | |
| +--------+ +--------+ |
| |
| +--------+ | +--------+
+---> | Via S2 | +---> | Via S2 |
| +--------+ +--------+
|
| +--------+
+---> | Via S3 |
| +---------+
|
| +--------+
+---> | Via S4 |
+--------+
Figure 23: Abstract RIB after Negative 2001:db8:1::/48 from S2
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Negative 2001:db8:1::/48 inherits from 2001:db8::/32 now, so the
positive more specific routes are the complements to S2 in the set of
next hops for 2001:db8::/32, which are S3 and S4, or, in other words,
all entries of the parent with the negative holes "punched in" again.
After the update, the FIB in T1 shows as illustrated in Figure 24:
+---------+ +---------------+ +-----------------+
| Default | | 2001:db8::/32 | | 2001:db8:1::/48 |
+---------+ +---------------+ +-----------------+
| | |
| +--------+ | |
+---> | Via S1 | | |
| +--------+ | |
| | |
| +--------+ | +--------+ |
+---> | Via S2 | +---> | Via S2 | |
| +--------+ | +--------+ |
| | |
| +--------+ | +--------+ | +--------+
+---> | Via S3 | +---> | Via S3 | +---> | Via S3 |
| +--------+ | +--------+ | +--------+
| | |
| +--------+ | +--------+ | +--------+
+---> | Via S4 | +---> | Via S4 | +---> | Via S4 |
+--------+ +--------+ +--------+
Figure 24: Abstract FIB after Negative 2001:db8:1::/48 from S2
Further, assume that S3 stops advertising its service as default
gateway. The entry is removed from RIB as usual. In order to update
the FIB, it is necessary to eliminate the FIB entry for the default
route, as well as all the FIB entries that were created for negative
routes pointing to the RIB entry being removed (::/0). This is done
recursively for 2001:db8::/32 and then for, 2001:db8:1::/48. The
related FIB entries via S3 are removed, as illustrated in Figure 25.
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+---------+ +---------------+ +-----------------+
| Default | | 2001:db8::/32 | | 2001:db8:1::/48 |
+---------+ +---------------+ +-----------------+
| | |
| +--------+ | |
+---> | Via S1 | | |
| +--------+ | |
| | |
| +--------+ | +--------+ |
+---> | Via S2 | +---> | Via S2 | |
| +--------+ | +--------+ |
| | |
| | |
| | |
| | |
| | |
| +--------+ | +--------+ | +--------+
+---> | Via S4 | +---> | Via S4 | +---> | Via S4 |
+--------+ +--------+ +--------+
Figure 25: Abstract FIB after Loss of S3
Say that at that time, S4 would also disaggregate prefix
2001:db8:1::/48. This would mean that the FIB entry for
2001:db8:1::/48 becomes a discard route, and that would be the signal
for T1 to disaggregate prefix 2001:db8:1::/48 negatively in a
transitive fashion with its own children.
Finally, the case occurs where S3 becomes available again as a
default gateway, and a negative advertisement is received from S4
about prefix 2001:db8:2::/48 as opposed to 2001:db8:1::/48. Again, a
negative route is stored in the RIB, and the more specific route to
the complementing ToF nodes are installed in FIB. Since
2001:db8:2::/48 inherits from 2001:db8::/32, the positive FIB routes
are chosen by removing S4 from S2, S3, S4. The abstract FIB in T1
now shows as illustrated in Figure 26:
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+-----------------+
| 2001:db8:2::/48 |
+-----------------+
|
+---------+ +---------------+ +-----------------+
| Default | | 2001:db8::/32 | | 2001:db8:1::/48 |
+---------+ +---------------+ +-----------------+
| | | |
| +--------+ | | | +--------+
+---> | Via S1 | | | +---> | Via S2 |
| +--------+ | | | +--------+
| | | |
| +--------+ | +--------+ | | +--------+
+---> | Via S2 | +---> | Via S2 | | +---> | Via S3 |
| +--------+ | +--------+ | +--------+
| | |
| +--------+ | +--------+ | +--------+
+---> | Via S3 | +---> | Via S3 | +---> | Via S3 |
| +--------+ | +--------+ | +--------+
| | |
| +--------+ | +--------+ | +--------+
+---> | Via S4 | +---> | Via S4 | +---> | Via S4 |
+--------+ +--------+ +--------+
Figure 26: Abstract FIB after Negative 2001:db8:2::/48 from S4
4.2.7. Optional Zero Touch Provisioning (ZTP)
Each RIFT node can operate in zero touch provisioning (ZTP) mode,
i.e. it has no configuration (unless it is a ToF or it is configured
to operate in the overall topology as leaf and/or support leaf-2-leaf
procedures) and it will fully configure itself after being attached
to the topology. Configured nodes and nodes operating in ZTP can be
mixed and will form a valid topology if achievable.
The derivation of the level of each node happens based on offers
received from its neighbors whereas each node (with possibly
exceptions of configured leaves) tries to attach at the highest
possible point in the fabric. This guarantees that even if the
diffusion front of offers reaches a node from "below" faster than
from "above", it will greedily abandon already negotiated level
derived from nodes topologically below it and properly peer with
nodes above.
The fabric is very consciously numbered from the top down to allow
for PoDs of different heights and minimize number of provisioning
necessary, in this case just a TOP_OF_FABRIC flag on every node at
the top of the fabric.
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This section describes the necessary concepts and procedures for ZTP
operation.
4.2.7.1. Terminology
The interdependencies between the different flags and the configured
level can be somewhat vexing at first and it may take multiple reads
of the glossary to comprehend them.
Automatic Level Derivation:
Procedures which allow nodes without level configured to derive it
automatically. Only applied if CONFIGURED_LEVEL is undefined.
UNDEFINED_LEVEL:
A "null" value that indicates that the level has not been
determined and has not been configured. Schemas normally indicate
that by a missing optional value without an available defined
default.
LEAF_ONLY:
An optional configuration flag that can be configured on a node to
make sure it never leaves the "bottom of the hierarchy".
TOP_OF_FABRIC flag and CONFIGURED_LEVEL cannot be defined at the
same time as this flag. It implies CONFIGURED_LEVEL value of
`leaf_level`. It is indicated in `leaf_only` schema element.
TOP_OF_FABRIC flag:
Configuration flag that MUST be provided to all Top-of-Fabric
nodes. LEAF_FLAG and CONFIGURED_LEVEL cannot be defined at the
same time as this flag. It implies a CONFIGURED_LEVEL value. In
fact, it is basically a shortcut for configuring same level at all
Top-of-Fabric nodes which is unavoidable since an initial 'seed'
is needed for other ZTP nodes to derive their level in the
topology. The flag plays an important role in fabrics with
multiple planes to enable successful negative disaggregation
(Section 4.2.5.2). It is carried in `top_of_fabric` schema
element. A standards conform RIFT implementation implies a
CONFIGURED_LEVEL value of `top_of_fabric_level` in case of
TOP_OF_FABRIC. This value is kept reasonably low to alow for fast
ZTP re-convergence on failures.
CONFIGURED_LEVEL:
A level value provided manually. When this is defined (i.e. it is
not an UNDEFINED_LEVEL) the node is not participating in ZTP in
the sense of deriving its own level based on other nodes'
information. TOP_OF_FABRIC flag is ignored when this value is
defined. LEAF_ONLY can be set only if this value is undefined or
set to `leaf_level`.
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DERIVED_LEVEL:
Level value computed via automatic level derivation when
CONFIGURED_LEVEL is equal to UNDEFINED_LEVEL.
LEAF_2_LEAF:
An optional flag that can be configured on a node to make sure it
supports procedures defined in Section 4.3.9. In a strict sense
it is a capability that implies LEAF_ONLY and the according
restrictions. TOP_OF_FABRIC flag is ignored when set at the same
time as this flag. It is carried in the
`leaf_only_and_leaf_2_leaf_procedures` schema flag.
LEVEL_VALUE:
In ZTP case the original definition of "level" in Section 3.1 is
both extended and relaxed. First, level is defined now as
LEVEL_VALUE and is the first defined value of CONFIGURED_LEVEL
followed by DERIVED_LEVEL. Second, it is possible for nodes to be
more than one level apart to form adjacencies if any of the nodes
is at least LEAF_ONLY.
Valid Offered Level (VOL):
A neighbor's level received on a valid LIE (i.e. passing all
checks for adjacency formation while disregarding all clauses
involving level values) persisting for the duration of the
holdtime interval on the LIE. Observe that offers from nodes
offering level value of `leaf_level` do not constitute VOLs (since
no valid DERIVED_LEVEL can be obtained from those and consequently
`not_a_ztp_offer` flag MUST be ignored). Offers from LIEs with
`not_a_ztp_offer` being true are not VOLs either. If a node
maintains parallel adjacencies to the neighbor, VOL on each
adjacency is considered as equivalent, i.e. the newest VOL from
any such adjacency updates the VOL received from the same node.
Highest Available Level (HAL):
Highest defined level value seen from all VOLs received.
Highest Available Level Systems (HALS):
Set of nodes offering HAL VOLs.
Highest Adjacency ThreeWay (HAT):
Highest neighbor level of all the formed ThreeWay adjacencies for
the node.
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4.2.7.2. Automatic System ID Selection
RIFT nodes require a 64 bit System ID which SHOULD be derived as
EUI-64 MA-L derive according to [EUI64]. The organizationally
governed portion of this ID (24 bits) can be used to generate
multiple IDs if required to indicate more than one RIFT instance."
As matter of operational concern, the router MUST ensure that such
identifier is not changing very frequently (or at least not without
sending all its TIEs with fairly short lifetimes, i.e. purging them)
since otherwise the network may be left with large amounts of stale
TIEs in other nodes (though this is not necessarily a serious problem
if the procedures described in Section 7 are implemented).
4.2.7.3. Generic Fabric Example
ZTP forces considerations of miscabled or unusually cabled fabric and
how such a topology can be forced into a "lattice" structure which a
fabric represents (with further restrictions). A necessary and
sufficient physical cabling is shown in Figure 27. The assumption
here is that all nodes are in the same PoD.
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+---+
| A | s = TOP_OF_FABRIC
| s | l = LEAF_ONLY
++-++ l2l = LEAF_2_LEAF
| |
+--+ +--+
| |
+--++ ++--+
| E | | F |
| +-+ | +-----------+
++--+ | ++-++ |
| | | | |
| +-------+ | |
| | | | |
| | +----+ | |
| | | | |
++-++ ++-++ |
| I +-----+ J | |
| | | +-+ |
++-++ +--++ | |
| | | | |
+---------+ | +------+ |
| | | | |
+-----------------+ | |
| | | | |
++-++ ++-++ |
| X +-----+ Y +-+
|l2l| | l |
+---+ +---+
Figure 27: Generic ZTP Cabling Considerations
First, RIFT must anchor the "top" of the cabling and that's what the
TOP_OF_FABRIC flag at node A is for. Then things look smooth until
the protocol has to decide whether node Y is at the same level as I,
J (and as consequence, X is south of it) or at the same level as X.
This is unresolvable here until we "nail down the bottom" of the
topology. To achieve that the protocol chooses to use in this
example the leaf flags in X and Y. In case where Y would not have a
leaf flag it will try to elect highest level offered and end up being
in same level as I and J.
4.2.7.4. Level Determination Procedure
A node starting up with UNDEFINED_VALUE (i.e. without a
CONFIGURED_LEVEL or any leaf or TOP_OF_FABRIC flag) MUST follow those
additional procedures:
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1. It advertises its LEVEL_VALUE on all LIEs (observe that this can
be UNDEFINED_LEVEL which in terms of the schema is simply an
omitted optional value).
2. It computes HAL as numerically highest available level in all
VOLs.
3. It chooses then MAX(HAL-1,0) as its DERIVED_LEVEL. The node then
starts to advertise this derived level.
4. A node that lost all adjacencies with HAL value MUST hold down
computation of new DERIVED_LEVEL for a short period of time
unless it has no VOLs from southbound adjacencies. After the
holddown timer expired, it MUST discard all received offers,
recompute DERIVED_LEVEL and announce it to all neighbors.
5. A node MUST reset any adjacency that has changed the level it is
offering and is in ThreeWay state.
6. A node that changed its defined level value MUST readvertise its
own TIEs (since the new `PacketHeader` will contain a different
level than before). Sequence number of each TIE MUST be
increased.
7. After a level has been derived the node MUST set the
`not_a_ztp_offer` on LIEs towards all systems offering a VOL for
HAL.
8. A node that changed its level SHOULD flush from its link state
database TIEs of all other nodes, otherwise stale information may
persist on "direction reversal", i.e. nodes that seemed south
are now north or east-west. This will not prevent the correct
operation of the protocol but could be slightly confusing
operationally.
A node starting with LEVEL_VALUE being 0 (i.e. it assumes a leaf
function by being configured with the appropriate flags or has a
CONFIGURED_LEVEL of 0) MUST follow those additional procedures:
1. It computes HAT per procedures above but does *not* use it to
compute DERIVED_LEVEL. HAT is used to limit adjacency formation
per Section 4.2.2.
It MAY also follow modified procedures:
1. It may pick a different strategy to choose VOL, e.g. use the VOL
value with highest number of VOLs. Such strategies are only
possible since the node always remains "at the bottom of the
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fabric" while another layer could "invert" the fabric by picking
its preferred VOL in a different fashion than always trying to
achieve the highest viable level.
4.2.7.5. ZTP FSM
This section specifies the precise, normative ZTP FSM and can be
omitted unless the reader is pursuing an implementation of the
protocol.
Initial state is ComputeBestOffer.
Enter
|
v
+------------------+
| ComputeBestOffer |
| |<----+
| | | BetterHAL
| | | BetterHAT
| | | ChangeLocalConfiguredLevel
| | | ChangeLocalHierarchyIndications
| | | LostHAT
| | | NeighborOffer
| | | ShortTic
| |-----+
| |
| |<---------------------
| |---------------------> (UpdatingClients)
| | ComputationDone
+------------------+
^ |
| | LostHAL
| V
(HoldingDown)
(ComputeBestOffer)
| ^
| | ChangeLocalConfiguredLevel
| | ChangeLocalHierarchyIndications
| | HoldDownExpired
V |
+------------------+
| HoldingDown |
| |<----+
| | | BetterHAL
| | | BetterHAT
| | | ComputationDone
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| | | LostHAL
| | | LostHat
| | | NeighborOffer
| | | ShortTic
| |-----+
+------------------+
^
|
(UpdatingClients)
(ComputeBestOffer)
| ^
| | BetterHAL
| | BetterHAT
| | LostHAT
| | ChangeLocalHierarchyIndications
| | ChangeLocalConfiguredLevel
V |
+------------------+
| UpdatingClients |
| |<----+
| | |
| | | NeighborOffer
| | | ShortTic
| |-----+
+------------------+
|
| LostHAL
V
(HoldingDown)
Figure 28: ZTP FSM
The following words are used for well known procedures:
* PUSH Event: queues an event to be executed by the FSM upon exit of
this action
* COMPARE_OFFERS: checks whether based on current offers and held
last results the events BetterHAL/LostHAL/BetterHAT/LostHAT are
necessary and returns them
* UPDATE_OFFER: store current offer with adjancency holdtime as
lifetime and COMPARE_OFFERS, then PUSH according events
* LEVEL_COMPUTE: compute best offered or configured level and HAL/
HAT, if anything changed PUSH ComputationDone
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* REMOVE_OFFER: remove the according offer and COMPARE_OFFERS, PUSH
according events
* PURGE_OFFERS: REMOVE_OFFER for all held offers, COMPARE OFFERS,
PUSH according events
* PROCESS_OFFER:
1. if no level offered then REMOVE_OFFER
2. else
1. if offered level > leaf then UPDATE_OFFER
2. else REMOVE_OFFER
States:
* ComputeBestOffer: processes received offers to derive ZTP
variables
* HoldingDown: holding down while receiving updates
* UpdatingClients: updates other FSMs with computation results
Events:
* ChangeLocalHierarchyIndications: node locally configured with new
leaf flags.
* ChangeLocalConfiguredLevel: node locally configured with a defined
level
* NeighborOffer: a new neighbor offer with optional level and
neighbor state.
* BetterHAL: better HAL computed internally.
* BetterHAT: better HAT computed internally.
* LostHAL: lost last HAL in computation.
* LostHAT: lost HAT in computation.
* ComputationDone: computation performed.
* HoldDownExpired: holddown timer expired.
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* ShortTic: one second timer tic, i.e. the event is generated for
FSM by some external entity once a second. To be ignored if
transition does not exist.
Actions:
* on ChangeLocalConfiguredLevel in HoldingDown finishes in
ComputeBestOffer: store configured level
* on BetterHAT in HoldingDown finishes in HoldingDown: no action
* on ShortTic in HoldingDown finishes in HoldingDown: remove expired
offers and if holddown timer expired PUSH_EVENT HoldDownExpired
* on NeighborOffer in HoldingDown finishes in HoldingDown:
PROCESS_OFFER
* on ComputationDone in HoldingDown finishes in HoldingDown: no
action
* on BetterHAL in HoldingDown finishes in HoldingDown: no action
* on LostHAT in HoldingDown finishes in HoldingDown: no action
* on LostHAL in HoldingDown finishes in HoldingDown: no action
* on HoldDownExpired in HoldingDown finishes in ComputeBestOffer:
PURGE_OFFERS
* on ChangeLocalHierarchyIndications in HoldingDown finishes in
ComputeBestOffer: store leaf flags
* on LostHAT in ComputeBestOffer finishes in ComputeBestOffer:
LEVEL_COMPUTE
* on NeighborOffer in ComputeBestOffer finishes in ComputeBestOffer:
PROCESS_OFFER
* on BetterHAT in ComputeBestOffer finishes in ComputeBestOffer:
LEVEL_COMPUTE
* on ChangeLocalHierarchyIndications in ComputeBestOffer finishes in
ComputeBestOffer: store leaf flags and LEVEL_COMPUTE
* on LostHAL in ComputeBestOffer finishes in HoldingDown: if any
southbound adjacencies present then update holddown timer to
normal duration else fire holddown timer immediately
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* on ShortTic in ComputeBestOffer finishes in ComputeBestOffer:
remove expired offers
* on ComputationDone in ComputeBestOffer finishes in
UpdatingClients: no action
* on ChangeLocalConfiguredLevel in ComputeBestOffer finishes in
ComputeBestOffer: store configured level and LEVEL_COMPUTE
* on BetterHAL in ComputeBestOffer finishes in ComputeBestOffer:
LEVEL_COMPUTE
* on ShortTic in UpdatingClients finishes in UpdatingClients: remove
expired offers
* on LostHAL in UpdatingClients finishes in HoldingDown: if any
southbound adjacencies present then update holddown timer to
normal duration else fire holddown timer immediately
* on BetterHAT in UpdatingClients finishes in ComputeBestOffer: no
action
* on BetterHAL in UpdatingClients finishes in ComputeBestOffer: no
action
* on ChangeLocalConfiguredLevel in UpdatingClients finishes in
ComputeBestOffer: store configured level
* on ChangeLocalHierarchyIndications in UpdatingClients finishes in
ComputeBestOffer: store leaf flags
* on NeighborOffer in UpdatingClients finishes in UpdatingClients:
PROCESS_OFFER
* on LostHAT in UpdatingClients finishes in ComputeBestOffer: no
action
* on Entry into ComputeBestOffer: LEVEL_COMPUTE
* on Entry into UpdatingClients: update all LIE FSMs with
computation results
4.2.7.6. Resulting Topologies
The procedures defined in Section 4.2.7.4 will lead to the RIFT
topology and levels depicted in Figure 29.
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+---+
| As|
| 24|
++-++
| |
+--+ +--+
| |
+--++ ++--+
| E | | F |
| 23+-+ | 23+-----------+
++--+ | ++-++ |
| | | | |
| +-------+ | |
| | | | |
| | +----+ | |
| | | | |
++-++ ++-++ |
| I +-----+ J | |
| 22| | 22| |
++--+ +--++ |
| | |
+---------+ | |
| | |
++-++ +---+ |
| X | | Y +-+
| 0 | | 0 |
+---+ +---+
Figure 29: Generic ZTP Topology Autoconfigured
In case where the LEAF_ONLY restriction on Y is removed the outcome
would be very different however and result in Figure 30. This
demonstrates basically that auto configuration makes miscabling
detection hard and with that can lead to undesirable effects in cases
where leaves are not "nailed" by the accordingly configured flags and
arbitrarily cabled.
A node MAY analyze the outstanding level offers on its interfaces and
generate warnings when its internal ruleset flags a possible
miscabling. As an example, when a node's sees ZTP level offers that
differ by more than one level from its chosen level (with proper
accounting for leaf's being at level `leaf_level`) this can indicate
miscabling.
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. +---+
. | As|
. | 24|
. ++-++
. | |
. +--+ +--+
. | |
. +--++ ++--+
. | E | | F |
. | 23+-+ | 23+-------+
. ++--+ | ++-++ |
. | | | | |
. | +-------+ | |
. | | | | |
. | | +----+ | |
. | | | | |
. ++-++ ++-++ +-+-+
. | I +-----+ J +-----+ Y |
. | 22| | 22| | 22|
. ++-++ +--++ ++-++
. | | | | |
. | +-----------------+ |
. | | |
. +---------+ | |
. | | |
. ++-++ |
. | X +--------+
. | 0 |
. +---+
Figure 30: Generic ZTP Topology Autoconfigured
4.3. Further Mechanisms
4.3.1. Route Preferences
Since RIFT distinguishes between different route types such as e.g.
external routes from other protocols and additionally advertises
special types of routes on disaggregation, the protocol MUST tie-
break internally different types on a clear preference scale to
prevent blackholes or loops. The preferences are given in the schema
type `RouteType`.
Table Table 5 contains the route type as derived from the TIE type
carrying it from the most preferred to the least preferred one.
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+==================================+======================+
| TIE Type | Resulting Route Type |
+==================================+======================+
| None | Discard |
+----------------------------------+----------------------+
| Local Interface | LocalPrefix |
+----------------------------------+----------------------+
| S-PGP | South PGP |
+----------------------------------+----------------------+
| N-PGP | North PGP |
+----------------------------------+----------------------+
| North Prefix | NorthPrefix |
+----------------------------------+----------------------+
| North External Prefix | NorthExternalPrefix |
+----------------------------------+----------------------+
| South Prefix and South Positive | SouthPrefix |
| Disaggregation | |
+----------------------------------+----------------------+
| South External Prefix and South | SouthExternalPrefix |
| Positive External Disaggregation | |
+----------------------------------+----------------------+
| South Negative Prefix | NegativeSouthPrefix |
+----------------------------------+----------------------+
Table 5: TIEs and Contained Route Types
4.3.2. Overload Bit
Overload attribute is specified in the packet encoding schema
(Appendix B).
The overload bit MUST be respected by all necessary SPF computations.
A node with the overload bit set SHOULD advertise all locally hosted
prefixes both northbound and southbound, all other southbound
prefixes SHOULD NOT be advertised.
Leaf nodes SHOULD set the overload attribute on all originated Node
TIEs. If spine nodes were to forward traffic not intended for the
local node, the leaf node would not be able to prevent routing/
forwarding loops as it does not have the necessary topology
information to do so.
4.3.3. Optimized Route Computation on Leaves
Leaf nodes only have visibility to directly connected nodes and
therefore are not required to run "full" SPF computations. Instead,
prefixes from neighboring nodes can be gathered to run a "partial"
SPF computation in order to build the routing table.
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Leaf nodes SHOULD only hold their own N-TIEs, and in cases of L2L
implementations, the N-TIEs of their East/West neighbors. Leaf nodes
MUST hold all S-TIEs from their neighbors.
Normally, a full network graph is created based on local N-TIEs and
remote S-TIEs that it receives from neighbors, at which time,
necessary SPF computations are performed. Instead, leaf nodes can
simply compute the minimum cost and next-hop set of each leaf
neighbor by examining its local adjacencies. Associated N-TIEs are
used to determine bi-directionality and derive the next-hop set.
Cost is then derived from the minimum cost of the local adjacency to
the neighbor and the prefix cost.
Leaf nodes would then attach necessary prefixes as described in
Section 4.2.6.
4.3.4. Mobility
The RIFT control plane MUST maintain the real time status of every
prefix, to which port it is attached, and to which leaf node that
port belongs. This is still true in cases of IP mobility where the
point of attachment may change several times a second.
There are two classic approaches to explicitly maintain this
information:
timestamp:
With this method, the infrastructure SHOULD record the precise
time at which the movement is observed. One key advantage of this
technique is that it has no dependency on the mobile device. One
drawback is that the infrastructure MUST be precisely synchronized
in order to be able to compare timestamps as the points of
attachment change. This could be accomplished by utilizing
Precision Time Protocol (PTP) IEEE Std. 1588 [IEEEstd1588] or
802.1AS [IEEEstd8021AS] which is designed for bridged LANs. Both
the precision of the synchronization protocol and the resolution
of the timestamp must beat the highest possible roaming time on
the fabric. Another drawback is that the presence of a mobile
device may only be observed asynchronously, such as when it starts
using an IP protocol like ARP [RFC0826], IPv6 Neighbor Discovery
[RFC4861], IPv6 Stateless Address Configuration [RFC4862], DHCP
[RFC2131], or DHCPv6 [RFC8415].
sequence counter:
With this method, a mobile device notifies its point of attachment
on arrival with a sequence counter that is incremented upon each
movement. On the positive side, this method does not have a
dependency on a precise sense of time, since the sequence of
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movements is kept in order by the mobile device. The disadvantage
of this approach is the lack of support for protocols that may be
used by the mobile device to register its presence to the leaf
node with the capability to provide a sequence counter. Well-
known issues with sequence counters such as wrapping and
comparison rules MUST be addressed properly. Sequence numbers
MUST be compared by a single homogenous source to make operation
feasible. Sequence number comparison from multiple heterogeneous
sources would be extremely difficult to implement.
RIFT supports a hybrid approach by using an optional
'PrefixSequenceType' attribute (that is also called a `monotonic
clock` in the schema) that consists of a timestamp and optional
sequence number field. In case of a negatively distributed prefix
this attribute MUST NOT be included by the originator and it MUST be
ignored by all nodes during computation. When this attribute is
present (observe that per data schema the attribute itself is
optional but in case it is included the 'timestamp' field is
required):
* The leaf node MAY advertise a timestamp of the latest sighting of
a prefix, e.g., by snooping IP protocols or the node using the
time at which it advertised the prefix. RIFT transports the
timestamp within the desired prefix North TIEs as 802.1AS
timestamp.
* RIFT MAY interoperate with "Registration Extensions for 6LoWPAN
Neighbor Discovery" [RFC8505], which provides a method for
registering a prefix with a sequence number called a Transaction
ID (TID). In such cases, RIFT SHOULD transport the derived TID
without modification.
* RIFT also defines an abstract negative clock (ASNC) (also called
an 'undefined' clock). ASNC MUST be considered older than any
other defined clock. By default, when a node receives a prefix
North TIE that does not contain a 'PrefixSequenceType' attribute,
it MUST interpret the absence as ASNC.
* Any prefix present on the fabric in multiple nodes that has the
`same` clock is considered as anycast.
* RIFT specification assumes that all nodes are being synchronized
to at least 200 milliseconds of precision. This is achievable
through the use of NTP [RFC5905]. An implementation MAY provide a
way to reconfigure a domain to a different value, and provides for
this purpose a variable called MAXIMUM_CLOCK_DELTA.
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4.3.4.1. Clock Comparison
All monotonic clock values MUST be compared to each other using the
following rules:
1. ASNC is older than any other value except ASNC *and*
2. Clock with timestamp differing by more than MAXIMUM_CLOCK_DELTA
are comparable by using the timestamps only *and*
3. Clocks with timestamps differing by less than MAXIMUM_CLOCK_DELTA
are comparable by using their TIDs only *and*
4. An undefined TID is always older than any other TID *and*
5. TIDs are compared using rules of [RFC8505].
4.3.4.2. Interaction between Time Stamps and Sequence Counters
For attachment changes that occur less frequently (e.g. once per
second), the timestamp that the RIFT infrastructure captures should
be enough to determine the most current discovery. If the point of
attachment changes faster than the maximum drift of the time stamping
mechanism (i.e. MAXIMUM_CLOCK_DELTA), then a sequence number SHOULD
be used to enable necessary precision to determine currency.
The sequence counter in [RFC8505] is encoded as one octet and wraps
around using Appendix A.
Within the resolution of MAXIMUM_CLOCK_DELTA, sequence counter values
captured during 2 sequential iterations of the same timestamp SHOULD
be comparable. This means that with default values, a node may move
up to 127 times in a 200 millisecond period and the clocks will
remain comparable. This allows the RIFT infrastructure to explicitly
assert the most up-to-date advertisement.
4.3.4.3. Anycast vs. Unicast
A unicast prefix can be attached to at most one leaf, whereas an
anycast prefix may be reachable via more than one leaf.
If a monotonic clock attribute is provided on the prefix, then the
prefix with the `newest` clock value is strictly preferred. An
anycast prefix does not carry a clock or all clock attributes MUST be
the same under the rules of Section 4.3.4.1.
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Observe that it is important that in mobility events the leaf is re-
flooding as quickly as possible the absence of the prefix that moved
away.
Observe further that without support for [RFC8505] movements on the
fabric within intervals smaller than 100msec will be seen as anycast.
4.3.4.4. Overlays and Signaling
RIFT is agnostic to any overlay technologies and their associated
control and transports that run on top of it (e.g. VXLAN). It is
expected that leaf nodes and possibly Top-of-Fabric nodes can perform
necessary data plane encapsulation.
In the context of mobility, overlays provide another possible
solution to avoid injecting mobile prefixes into the fabric as well
as improving scalability of the deployment. It makes sense to
consider overlays for mobility solutions in IP fabrics. As an
example, a mobility protocol such as LISP [RFC6830] may inform the
ingress leaf of the location of the egress leaf in real time.
Another possibility is to consider that mobility as an underlay
service and support it in RIFT to an extent. The load on the fabric
augments with the amount of mobility obviously since a move forces
flooding and computation on all nodes in the scope of the move so
tunneling from leaf to the Top-of-Fabric may be desired to speed up
convergence times.
4.3.5. Key/Value Store
4.3.5.1. Southbound
RIFT supports the southbound distribution of key-value pairs that can
be used to distribute information to facilitate higher levels of
functionality (e.g. distribution of configuration information). KV
South TIEs may arrive from multiple nodes and therefore MUST execute
the following tie-breaking rules for each key:
1. Only KV TIEs received from nodes to which a bi-directional
adjacency exists MUST be considered.
2. For each valid KV South TIEs that contains the same key, the
value within the South TIE with the highest level will be
preferred. If the levels are identical, the highest originating
system ID will be preferred. In the case of overlapping keys in
the winning South TIE, the behavior is undefined.
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Consider that if a node goes down, nodes south of it will lose
associated adjacencies causing them to disregard corresponding KVs.
New KV South TIEs are advertised to prevent stale information being
used by nodes that are farther south. KV advertisements southbound
are not a result of independent computation by every node over the
same set of South TIEs, but a diffused computation.
4.3.5.2. Northbound
Certain use cases necessitate distribution of essential KV
information that is generated by the leaves in the northbound
direction. Such information is flooded in KV North TIEs. Since the
originator of the KV North TIEs is preserved during flooding, the
according mechanism will define, if necessary, according tie-breaking
rules depending on the semantics of the information.
Only KV TIEs from nodes that are reachable via multiplane
reachability computation mentioned in Section 4.2.5.2.3 SHOULD be
considered.
4.3.6. Interactions with BFD
RIFT MAY incorporate BFD [RFC5881] to react quickly to link failures.
In such case following procedures are introduced:
After RIFT ThreeWay hello adjacency convergence a BFD session MAY
be formed automatically between the RIFT endpoints without further
configuration using the exchanged discriminators. The capability
of the remote side to support BFD is carried in the LIEs in
`LinkCapabilities`.
In case established BFD session goes Down after it was Up, RIFT
adjacency SHOULD be re-initialized and subsequently started from
Init after it sees a consecutive BFD Up.
In case of parallel links between nodes each link MAY run its own
independent BFD session or they MAY share a session.
If link identifiers or BFD capabilities change, both the LIE and
any BFD sessions SHOULD be brought down and back up again. In
case only the advertised capabilities change, the node MAY choose
to persist the BFD session.
Multiple RIFT instances MAY choose to share a single BFD session,
in such cases the behavior for which discriminators are used is
undefined. However, RIFT MAY advertise the same link ID for the
same interface in multiple instances to "share" discriminators.
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BFD TTL follows [RFC5082].
4.3.7. Fabric Bandwidth Balancing
A well understood problem in fabrics is that in case of link
failures, it would be ideal to rebalance how much traffic is sent to
switches in the next level based on available ingress and egress
bandwidth.
RIFT supports a very light weight mechanism that can deal with the
problem in an approximate way based on the fact that RIFT is loop-
free.
4.3.7.1. Northbound Direction
Every RIFT node SHOULD compute the amount of northbound bandwidth
available through neighbors at higher level and modify distance
received on default route from this neighbor. The bandwidth is
advertised in `NodeNeighborsTIEElement` element which represents the
sum of the bandwidths of all the parallel links to a neighbor.
Default routes with differing distances SHOULD be used to support
weighted ECMP forwarding. Such a distance is called Bandwidth
Adjusted Distance or BAD. This is best illustrated by a simple
example.
100 x 100 100 MBits
| x | |
+-+---+-+ +-+---+-+
| | | |
|Spin111| |Spin112|
+-+---+++ ++----+++
|x || || ||
|| |+---------------+ ||
|| +---------------+| ||
|| || || ||
|| || || ||
-----All Links 10 MBit-------
|| || || ||
|| || || ||
|| +------------+| || ||
|| |+------------+ || ||
|x || || ||
+-+---+++ +--++-+++
| | | |
|Leaf111| |Leaf112|
+-------+ +-------+
Figure 31: Balancing Bandwidth
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Figure 31 depicts an example topology where links between leaf and
spine nodes are 10 MBit/s and links from spine nodes northbound are
100 MBit/s. It includes parallel link failure between Leaf 111 and
Spine 111 and as a result, Leaf 111 wants to forward more traffic
toward Spine 112. Additionally, it includes as well an uplink
failure on Spine 111.
The local modification of the received default route distance from
upper level is achieved by running a relatively simple algorithm
where the bandwidth is weighted exponentially, while the distance on
the default route represents a multiplier for the bandwidth weight
for easy operational adjustments.
On a node, L, use Node TIEs to compute from each non-overloaded
northbound neighbor N to compute 3 values:
L_N_u: as sum of the bandwidth available to N
N_u: as sum of the uplink bandwidth available on N
T_N_u: as sum of L_N_u * OVERSUBSCRIPTION_CONSTANT + N_u
For all T_N_u determine the according M_N_u as
log_2(next_power_2(T_N_u)) and determine MAX_M_N_u as maximum value
of all such M_N_u values.
For each advertised default route from a node N modify the advertised
distance D to BAD = D * (1 + MAX_M_N_u - M_N_u) and use BAD instead
of distance D to weight balance default forwarding towards N.
For the example above, a simple table of values will help in
understanding of the concept. The implicit assumption here is that
all default route distances are advertised with D=1 and that
OVERSUBSCRIPTION_CONSTANT = 1.
+=========+===========+=======+=======+=====+
| Node | N | T_N_u | M_N_u | BAD |
+=========+===========+=======+=======+=====+
| Leaf111 | Spine 111 | 110 | 7 | 2 |
+---------+-----------+-------+-------+-----+
| Leaf111 | Spine 112 | 220 | 8 | 1 |
+---------+-----------+-------+-------+-----+
| Leaf112 | Spine 111 | 120 | 7 | 2 |
+---------+-----------+-------+-------+-----+
| Leaf112 | Spine 112 | 220 | 8 | 1 |
+---------+-----------+-------+-------+-----+
Table 6: BAD Computation
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If a calculation produces a result exceeding the range of the type,
e.g. bandwidth, the result is set to the highest possible value for
that type.
BAD SHOULD be only computed for default routes. A node MAY compute
and use BAD for any disaggregated prefixes or other RIFT routes. A
node MAY use a different algorithm to weight northbound traffic based
on bandwidth. If a different algorithm is used, its successful
behavior MUST NOT depend on uniformity of algorithm or
synchronization of BAD computations across the fabric. E.g. it is
conceivable that leaves could use real time link loads gathered by
analytics to change the amount of traffic assigned to each default
route next hop.
Furthermore, a change in available bandwidth will only affect, at
most, two levels down in the fabric, i.e. the blast radius of
bandwidth adjustments is constrained no matter the fabric's height.
4.3.7.2. Southbound Direction
Due to its loop free nature, during South SPF, a node MAY account for
maximum available bandwidth on nodes in lower levels and modify the
amount of traffic offered to the next level's southbound nodes. It
is worth considering that such computations may be more effective if
standardized, but do not have to be. As long as a packet continues
to flow southbound, it will take some viable, loop-free path to reach
its destination.
4.3.8. Label Binding
A node MAY advertise in its LIEs, a locally significant, downstream
assigned, interface specific label. One use of such a label is a
hop-by-hop encapsulation allowing forwarding planes to be easily
distinguished among multiple RIFT instances.
4.3.9. Leaf to Leaf Procedures
RIFT implementations SHOULD support special East-West adjacencies
between leaf nodes. Leaf nodes supporting these procedures MUST:
advertise the LEAF_2_LEAF flag in its node capabilities *and*
set the overload bit on all leaf's node TIEs *and*
flood only a node's own north and south TIEs over E-W leaf
adjacencies *and*
always use E-W leaf adjacency in all SPF computations *and*
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install a discard route for any advertised aggregate routes in a
leaf?s TIE *and*
never form southbound adjacencies.
This will allow the E-W leaf nodes to exchange traffic strictly for
the prefixes advertised in each other's north prefix TIEs (since the
southbound computation will find the reverse direction in the other
node's TIE and install its north prefixes).
4.3.10. Address Family and Multi Topology Considerations
Multi-Topology (MT)[RFC5120] and Multi-Instance (MI)[RFC8202]
concepts are used today in link-state routing protocols to support
several domains on the same physical topology. RIFT supports this
capability by carrying transport ports in the LIE protocol exchanges.
Multiplexing of LIEs can be achieved by either choosing varying
multicast addresses or ports on the same address.
BFD interactions in Section 4.3.6 are implementation dependent when
multiple RIFT instances run on the same link.
4.3.11. One-Hop Healing of Levels with East-West Links
Based on the rules defined in Section 4.2.4, Section 4.2.3.8 and
given presence of E-W links, RIFT can provide a one-hop protection
for nodes that lost all their northbound links. This can also be
applied to multi-plane designs where complex link set failures occur
at the Top-of-Fabric when links are exclusively used for flooding
topology information. Section 5.4 outlines this behavior.
4.4. Security
4.4.1. Security Model
An inherent property of any security and ZTP architecture is the
resulting trade-off in regard to integrity verification of the
information distributed through the fabric vs. provisioning and auto-
configuration requirements. At a minimum the security of an
established adjacency should be ensured. The stricter the security
model the more provisioning must take over the role of ZTP.
RIFT supports the following security models to allow for flexible
control by the operator.
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* The most security conscious operators may choose to have control
over which ports interconnect between a given pair of nodes, such
a model is called the "Port-Association Model" (PAM). This is
achievable by configuring each pair of directly connected ports
with a designated shared key or public/private key pair.
* In physically secure data center locations, operators may choose
to control connectivity between entire nodes, called here the
"Node-Association Model" (NAM). A benefit of this model is that
it allows for simplified port sparing.
* In the most relaxed environments, an operator may only choose to
control which nodes join a particular fabric. This is denoted as
the "Fabric-Association Model" (FAM). This is achievable by using
a single shared secret across the entire fabric. Such flexibility
makes sense when servers are considered as leaf devices, as those
are replaced more often than network nodes. In addition, this
model allows for simplified node sparing.
* These models may be mixed throughout the fabric depending upon
security requirements at various levels of the fabric and
willingness to accept increased provisioning complexity.
In order to support the cases mentioned above, RIFT implementations
supports, through operator control, mechanisms that allow for:
a. specification of the appropriate level in the fabric,
b. discovery and reporting of missing connections,
c. discovery and reporting of unexpected connections while
preventing them from forming insecure adjacencies.
Operators may only choose to configure the level of each node, but
not explicitly configure which connections are allowed. In this
case, RIFT will only allow adjacencies to establish between nodes
that are in adjacent levels. Operators with the lowest security
requirements may not use any configuration to specify which
connections are allowed. Nodes in such fabrics could rely fully on
ZTP and only established adjacencies between nodes in adjacent
levels. Figure 32 illustrates inherent tradeoffs between the
different security models.
Some level of link quality verification may be required prior to an
adjacency being used for forwarding. For example, an implementation
may require that a BFD session comes up before advertising the
adjacency.
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For the cases outlined above, RIFT has two approaches to enforce that
a local port is connected to the correct port on the correct remote
node. One approach is to piggy-back on RIFT's authentication
mechanism. Assuming the provisioning model (e.g. the YANG model) is
flexible enough, operators can choose to provision a unique
authentication key for:
a. each pair of ports in "port-association model" or
b. each pair of switches in "node-association model" or
c. each pair of levels or
d. the entire fabric in "fabric-association model".
The other approach is to rely on the system-id, port-id and level
fields in the LIE message to validate an adjacency against the
expected cabling topology, and optionally introduce some new rules in
the FSM to allow the adjacency to come up if the expectations are
met.
^ /\ |
/|\ / \ |
| / \ |
| / PAM \ |
Increasing / \ Increasing
Integrity +----------+ Flexibility
& / NAM \ &
Increasing +--------------+ Less
Provisioning / FAM \ Configuration
| +------------------+ |
| / Level Provisioning \ |
| +----------------------+ \|/
| / Zero Configuration \ v
+--------------------------+
Figure 32: Security Model
4.4.2. Security Mechanisms
RIFT Security goals are to ensure:
1. authentication
2. message integrity
3. the prevention of replay attacks
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4. low processing overhead
5. efficient messaging
Message confidentiality is a non-goal.
The model in the previous section allows a range of security key
types that are analogous to the various security association models.
PAM and NAM allow security associations at the port or node level
using symmetric or asymmetric keys that are pre-installed. FAM
argues for security associations to be applied only at a group level
or to be refined once the topology has been established. RIFT does
not specify how security keys are installed or updated, though it
does specify how the key can be used to achieve security goals.
The protocol has provisions for "weak" nonces to prevent replay
attacks and includes authentication mechanisms comparable to
[RFC5709] and [RFC7987].
4.4.3. Security Envelope
A serialized schema `ProtocolPacket` MUST be carried in a secure
envelope illustrated in Figure 33. Any value in the packet following
a security fingerprint MUST be used only after the appropriate
fingerprint has been validated against the data covered by it and
advertised key.
Local configuration MAY allow for the envelope's integrity checks to
be skipped.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
UDP Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | RIFT destination port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UDP Length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Outer Security Envelope Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RIFT MAGIC | Packet Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | RIFT Major | Outer Key ID | Fingerprint |
| | Version | | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Security Fingerprint covers all following content ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Weak Nonce Local | Weak Nonce Remote |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remaining TIE Lifetime (all 1s in case of LIE) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TIE Origin Security Envelope Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TIE Origin Key ID | Fingerprint |
| | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Security Fingerprint covers all following content ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Serialized RIFT Model Object
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Serialized RIFT Model Object ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 33: Security Envelope
RIFT MAGIC:
16 bits. Constant value of 0xA1F7 that allows to classify RIFT
packets easily independent of UDP port used.
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Packet Number:
16 bits. An optional, per adjacency, per packet type
monotonically increasing number rolling over using sequence number
arithmetic defined in Appendix A. A node SHOULD correctly set the
number on subsequent packets or otherwise MUST set the value to
`undefined_packet_number` as provided in the schema. This number
can be used to detect losses and misordering in flooding for
either operational purposes or in implementation to adjust
flooding behavior to current link or buffer quality. This number
MUST NOT be used to discard or validate the correctness of
packets. Packet numbers are incremented on each interface and
within that for each type of packet independently. This allows to
parallelize packet generation and processing for different types
within an implementation if so desired.
RIFT Major Version:
8 bits. It allows to check whether protocol versions are
compatible, i.e. if the serialized object can be decoded at all.
An implementation MUST drop packets with unexpected values and MAY
report a problem.
Outer Key ID:
8 bits to allow key rollovers. This implies key type and
algorithm. Value `invalid_key_value_key` means that no valid
fingerprint was computed. This key ID scope is local to the nodes
on both ends of the adjacency.
TIE Origin Key ID:
24 bits. This implies key type and used algorithm. Value
`invalid_key_value_key` means that no valid fingerprint was
computed. This key ID scope is global to the RIFT instance since
it may imply the originator of the TIE so the contained object
does not have to be de-serialized to obtain the originator.
Length of Fingerprint:
8 bits. Length in 32-bit multiples of the following fingerprint
(not including lifetime or weak nonces). It allows the structure
to be navigated when an unknown key type is present. To clarify,
a common corner case when this value is set to 0 is when it
signifies an empty (0 bytes long) security fingerprint.
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Security Fingerprint:
32 bits * Length of Fingerprint. This is a signature that is
computed over all data following after it. If the significant
bits of fingerprint are fewer than the 32 bits padded length than
the significant bits MUST be left aligned and remaining bits on
the right padded with 0s. When using PKI the Security fingerprint
originating node uses its private key to create the signature.
The original packet can then be verified provided the public key
is shared and current.
Remaining TIE Lifetime:
32 bits. In case of anything but TIEs this field MUST be set to
all ones and Origin Security Envelope Header MUST NOT be present
in the packet. For TIEs this field represents the remaining
lifetime of the TIE and Origin Security Envelope Header MUST be
present in the packet.
Weak Nonce Local:
16 bits. Local Weak Nonce of the adjacency as advertised in LIEs.
Weak Nonce Remote:
16 bits. Remote Weak Nonce of the adjacency as received in LIEs.
TIE Origin Security Envelope Header:
It MUST be present if and only if the Remaining TIE Lifetime field
is *not* all ones. It carries through the originators key ID and
according fingerprint of the object to protect TIE from
modification during flooding. This ensures origin validation and
integrity (but does not provide validation of a chain of trust).
Observe that due to the schema migration rules per Appendix B the
contained model can be always decoded if the major version matches
and the envelope integrity has been validated. Consequently,
description of the TIE is available to flood it properly including
unknown TIE types.
4.4.4. Weak Nonces
The protocol uses two 16 bit nonces to salt generated signatures.
The term "nonce" is used a bit loosely since RIFT nonces are not
being changed in every packet as often common in cryptography. For
efficiency purposes they are changed at a high enough frequency to
dwarf practical replay attack attempts. And hence, such nonces are
called from this point on "weak" nonces.
Any implementation including RIFT security MUST generate and wrap
around local nonces properly. When a nonce increment leads to
`undefined_nonce` value, the value MUST be incremented again
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immediately. All implementation MUST reflect the neighbor's nonces.
An implementation SHOULD increment a chosen nonce on every LIE FSM
transition that ends up in a different state from the previous one
and MUST increment its nonce at least every
`nonce_regeneration_interval` (such considerations allow for
efficient implementations without opening a significant security
risk). When flooding TIEs, the implementation MUST use recent (i.e.
within allowed difference) nonces reflected in the LIE exchange. The
schema specifies in `maximum_valid_nonce_delta` the maximum allowable
nonce value difference on a packet compared to reflected nonces in
the LIEs. Any packet received with nonces deviating more than the
allowed delta MUST be discarded without further computation of
signatures to prevent computation load attacks. The delta is either
a negative or positive difference that a mirrored nonce can deviate
from local value to be considered valid. If nonces are not changed
on every packet but at the maximum interval on both sides this opens
statistically a `maximum_valid_nonce_delta`/2 window of identical
LIEs, TIE and TI(x)E replays. The interval cannot be too small since
LIE FSM may change states fairly quickly during ZTP without sending
LIEs and additionally, UDP can both loose as well as misorder
packets.
In cases where a secure implementation does not receive signatures or
receives undefined nonces from a neighbor (indicating that it does
not support or verify signatures), it is a matter of local policy as
to how those packets are treated. A secure implementation MAY refuse
forming an adjacency with an implementation that is not advertising
signatures or valid nonces, or it MAY continue signing local packets
while accepting a neighbor's packets without further security
validation.
As a necessary exception, an implementation MUST advertise the remote
nonce value as `undefined_nonce` when the FSM is not in TwoWay or
ThreeWay state and accept an `undefined_nonce` for its local nonce
value on packets in any other state than ThreeWay.
As optional optimization, an implementation MAY send one LIE with
previously negotiated neighbor's nonce to try to speed up a
neighbor's transition from ThreeWay to OneWay and MUST revert to
sending `undefined_nonce` after that.
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4.4.5. Lifetime
Protecting flooding lifetime may lead to an excessive number of
security fingerprint computations and to avoid this the application
generating the fingerprints for advertised TIEs MAY round the value
down to the next `rounddown_lifetime_interval`. This will limit the
number of computations performed for security purposes caused by
lifetime attacks as long the weak nonce did not advance.
4.5. Security Association Changes
There in no mechanism to convert a security envelope for the same key
ID from one algorithm to another once the envelope is operational.
The recommended procedure to change to a new algorithm is to take the
adjacency down, make the necessary changes, and bring the adjacency
back up. Obviously, an implementation MAY choose to stop verifying
security envelope for the duration of algorithm change to keep the
adjacency up but since this introduces a security vulnerability
window, such roll-over SHOULD NOT be recommended.
5. Examples
5.1. Normal Operation
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^ N +--------+ +--------+
Level 2 | |ToF 21| |ToF 22|
E <-*-> W ++-+--+-++ ++-+--+-++
| | | | | | | | |
S v P111/2 |P121/2 | | | |
^ ^ ^ ^ | | | |
| | | | | | | |
+--------------+ | +-----------+ | | | +---------------+
| | | | | | | |
South +-----------------------------+ | | ^
| | | | | | | All TIEs
0/0 0/0 0/0 +-----------------------------+ |
v v v | | | | |
| | +-+ +<-0/0----------+ | |
| | | | | | | |
+-+----++ +-+----++ ++----+-+ ++-----++
Level 1 | | | | | | | |
|Spin111| |Spin112| |Spin121| |Spin122|
+-+---+-+ ++----+-+ +-+---+-+ ++---+--+
| | | South | | | |
| +---0/0--->-----+ 0/0 | +----------------+ |
0/0 | | | | | | |
| +---<-0/0-----+ | v | +--------------+ | |
v | | | | | | |
+-+---+-+ +--+--+-+ +-+---+-+ +---+-+-+
Level 0 | | | | | | | |
|Leaf111| |Leaf112| |Leaf121| |Leaf122|
+-+-----+ +-+---+-+ +--+--+-+ +-+-----+
+ + \ / + +
Prefix111 Prefix112 \ / Prefix121 Prefix122
multi-homed
Prefix
+---------- PoD 1 ---------+ +---------- PoD 2 ---------+
Figure 34: Normal Case Topology
This section describes RIFT deployment in example topology given in
Figure 34 without any node or link failures. The scenario disregards
flooding reduction for simplicity's sake and compresses the node
names in some cases to fit them into the picture better.
First, the following bi-directional adjacencies will be established:
1. ToF 21 (PoD 0) to Spine 111, Spine 112, Spine 121, and Spine 122
2. ToF 22 (PoD 0) to Spine 111, Spine 112, Spine 121, and Spine 122
3. Spine 111 to Leaf 111, Leaf 112
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4. Spine 112 to Leaf 111, Leaf 112
5. Spine 121 to Leaf 121, Leaf 122
6. Spine 122 to Leaf 121, Leaf 122
Leaf 111 and Leaf 112 originate N-TIEs for Prefix 111 and Prefix 112
(respectively) to both Spine 111 and Spine 112 (Leaf 112 also
originates an N-TIE for the multi-homed prefix). Spine 111 and Spine
112 will then originate their own N-TIEs, as well as flood the N-TIEs
received from Leaf 111 and Leaf 112 to both ToF 21 and ToF 22.
Similarly, Leaf 121 and Leaf 122 originate North TIEs for Prefix 121
and Prefix 122 (respectively) to Spine 121 and Spine 122 (Leaf 121
also originates an North TIE for the multi-homed prefix). Spine 121
and Spine 122 will then originate their own North TIEs, as well as
flood the North TIEs received from Leaf 121 and Leaf 122 to both ToF
21 and ToF 22.
Spines hold only North TIEs of level 0 for their PoD, while leaves
only hold their own North TIEs while at this point, both ToF 21 and
ToF 22 (as well as any northbound connected controllers) would have
the complete network topology.
ToF 21 and ToF 22 would then originate and flood South TIEs
containing any established adjacencies and a default IP route to all
spines. Spine 111, Spine 112, Spine 121, and Spine 122 will reflect
all Node South TIEs received from ToF 21 to ToF 22, and all Node
South TIEs from ToF 22 to ToF 21. South TIEs will not be re-
propagated southbound.
South TIEs containing a default IP route are then originated by both
Spine 111 and Spine 112 toward Leaf 111 and Leaf 112. Similarly,
South TIEs containing a default IP route are originated by Spine 121
and Spine 122 toward Leaf 121 and Leaf 122.
At this point IP connectivity across maximum number of viable paths
has been established for all leaves, with routing information
constrained to only the minimum amount that allows for normal
operation and redundancy.
5.2. Leaf Link Failure
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| | | |
+-+---+-+ +-+---+-+
| | | |
|Spin111| |Spin112|
+-+---+-+ ++----+-+
| | | |
| +---------------+ X
| | | X Failure
| +-------------+ | X
| | | |
+-+---+-+ +--+--+-+
| | | |
|Leaf111| |Leaf112|
+-------+ +-------+
+ +
Prefix111 Prefix112
Figure 35: Single Leaf Link Failure
In the event of a link failure between Spine 112 and Leaf 112, both
nodes will originate new Node TIEs that contain their connected
adjacencies, except for the one that just failed. Leaf 112 will send
a Node North TIE to Spine 111. Spine 112 will send a Node North TIE
to ToF 21 and ToF 22 as well as a new Node South TIE to Leaf 111 that
will be reflected to Spine 111. Necessary SPF recomputation will
occur, resulting in Spine 112 no longer being in the forwarding path
for Prefix 112.
Spine 111 will also disaggregate Prefix 112 by sending new Prefix
South TIE to Leaf 111 and Leaf 112. Though disaggregation is covered
in more detail in the following section, it is worth mentioning ini
this example as it further illustrates RIFT's blackhole mitigation
mechanism. Consider that Leaf 111 has yet to receive the more
specific (disaggregated) route from Spine 111. In such a scenario,
traffic from Leaf 111 toward Prefix 112 may still use Spine 112's
default route, causing it to traverse ToF 21 and ToF 22 back down via
Spine 111. While this behavior is suboptimal, it is transient in
nature and preferred to black-holing traffic.
5.3. Partitioned Fabric
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+--------+ +--------+
Level 2 |ToF 21| |ToF 22|
++-+--+-++ ++-+--+-++
| | | | | | | |
| | | | | | | 0/0
| | | | | | | |
| | | | | | | |
+--------------+ | +--- XXXXXX + | | | +---------------+
| | | | | | | |
| +-----------------------------+ | | |
0/0 | | | | | | |
| 0/0 0/0 +- XXXXXXXXXXXXXXXXXXXXXXXXX -+ |
| 1.1/16 | | | | | |
| | +-+ +-0/0-----------+ | |
| | | 1.1./16 | | | |
+-+----++ +-+-----+ ++-----0/0 ++----0/0
Level 1 | | | | | 1.1/16 | 1.1/16
|Spin111| |Spin112| |Spin121| |Spin122|
+-+---+-+ ++----+-+ +-+---+-+ ++---+--+
| | | | | | | |
| +---------------+ | | +----------------+ |
| | | | | | | |
| +-------------+ | | | +--------------+ | |
| | | | | | | |
+-+---+-+ +--+--+-+ +-+---+-+ +---+-+-+
Level 3 | | | | | | | |
|Leaf111| |Leaf112| |Leaf121| |Leaf122|
+-+-----+ ++------+ +-----+-+ +-+-----+
+ + + +
Prefix111 Prefix112 Prefix121 Prefix122
1.1/16
Figure 36: Fabric Partition
Figure 36 shows one of more catastrophic scenarios where ToF 21 is
completely severed from access to Prefix 121 due to a double link
failure. If only default routes existed, this would result in 50% of
traffic from Leaf 111 and Leaf 112 toward Prefix 121 being black-
holed.
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The mechanism to resolve this scenario hinges on ToF 21's South TIEs
being reflected from Spine 111 and Spine 112 to ToF 22. Once ToF 22
sees that Prefix 121 cannot be reached from ToF 21, it will begin to
disaggregate Prefix 121 by advertising a more specific route (1.1/16)
along with the default IP prefix route to all spines (ToF 21 still
only sends a default route). The result is Spine 111 and Spine112
using the more specific route to Prefix 121 via ToF 22. All other
prefixes continue to use the default IP prefix route toward both ToF
21 and ToF 22.
The more specific route for Prefix 121 being advertised by ToF 22
does not need to be propagated further south to the leaves, as they
do not benefit from this information. Spine 111 and Spine 112 are
only required to reflect the new South Node TIEs received from ToF 22
to ToF 21. In short, only the relevant nodes received the relevant
updates, thereby restricting the failure to only the partitioned
level rather than burdening the whole fabric with the flooding and
recomputation of the new topology information.
To finish this example, the following table shows sets computed by
ToF 22 using notation introduced in Section 4.2.5:
|R = Prefix 111, Prefix 112, Prefix 121, Prefix 122
|H (for r=Prefix 111) = Spine 111, Spine 112
|H (for r=Prefix 112) = Spine 111, Spine 112
|H (for r=Prefix 121) = Spine 121, Spine 122
|H (for r=Prefix 122) = Spine 121, Spine 122
|A (for ToF 21) = Spine 111, Spine 112
With that and |H (for r=Prefix 121) and |H (for r=Prefix 122) being
disjoint from |A (for ToF 21), ToF 22 will originate an South TIE
with Prefix 121 and Prefix 122, which will be flooded to all spines.
5.4. Northbound Partitioned Router and Optional East-West Links
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+ + +
X N1 | N2 | N3
X | |
+--+----+ +--+----+ +--+-----+
| |0/0> <0/0| |0/0> <0/0| |
| A01 +----------+ A02 +----------+ A03 | Level 1
++-+-+--+ ++--+--++ +---+-+-++
| | | | | | | | |
| | +----------------------------------+ | | |
| | | | | | | | |
| +-------------+ | | | +--------------+ |
| | | | | | | | |
| +----------------+ | +-----------------+ |
| | | | | | | | |
| | +------------------------------------+ | |
| | | | | | | | |
++-+-+--+ | +---+---+ | +-+---+-++
| | +-+ +-+ | |
| L01 | | L02 | | L03 | Level 0
+-------+ +-------+ +--------+
Figure 37: North Partitioned Router
Figure 37 shows a part of a fabric where level 1 is horizontally
connected and A01 lost its only northbound adjacency. Based on N-SPF
rules in Section 4.2.4.1 A01 will compute northbound reachability by
using the link A01 to A02. A02 however, will *not* use this link
during N-SPF. The result is A01 utilizing the horizontal link for
default route advertisement and unidirectional routing.
Furthermore, if A02 also loses its only northbound adjacency (N2),
the situation evolves. A01 will no longer have northbound
reachability while it sees A03's northbound adjacencies in South Node
TIEs reflected by nodes south of it. As a result, A01 will no longer
advertise its default route in accordance with Section 4.2.3.8.
6. Further Details on Implementation
6.1. Considerations for Leaf-Only Implementation
RIFT can and is intended to be stretched to the lowest level in the
IP fabric to integrate ToRs or even servers. Since those entities
would run as leaves only, it is worth to observe that a leaf only
version is significantly simpler to implement and requires much less
resources:
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1. Leaf nodes only need to maintain a multipath default route under
normal circumstances. However, in cases of catastrophic
partitioning, leaf nodes SHOULD be capable of accommodating all
the leaf routes in its own PoD to prevent black-holing.
2. Leaf nodes hold only their own North TIEs and South TIEs of Level
1 nodes they are connected to.
3. Leaf nodes do not have to support any type of disaggregation
computation or propagation.
4. Leaf nodes are not required to support overload bit.
5. Leaf nodes do not need to originate S-TIEs unless optional leaf-
2-leaf features are desired.
6.2. Considerations for Spine Implementation
Nodes that do not act as ToF are not required to discover fallen
leaves by comparing reachable destinations with peers and therefore
do not need to run the computation of disaggregated routes based on
that discovery. On the other hand, non-ToF nodes need to respect
disaggregated routes advertised from the north. In the case of
negative disaggregation, spines nodes need to generate southbound
disaggregated routes when all parents are lost for a fallen leaf.
7. Security Considerations
7.1. General
One can consider attack vectors where a router may reboot many times
while changing its system ID and pollute the network with many stale
TIEs or TIEs are sent with very long lifetimes and not cleaned up
when the routes vanish. Those attack vectors are not unique to RIFT.
Given large memory footprints available today those attacks should be
relatively benign. Otherwise a node SHOULD implement a strategy of
discarding contents of all TIEs that were not present in the SPF tree
over a certain, configurable period of time. Since the protocol,
like all modern link-state protocols, is self-stabilizing and will
advertise the presence of such TIEs to its neighbors, they can be re-
requested again if a computation finds that it sees an adjacency
formed towards the system ID of the discarded TIEs.
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7.2. Malformed Packets
The protocol protects packets extensively through optional signatures
and nonces so if the possibility of maliciously injected malformed or
replayed packets exist in a deployment, this conclusively protects
against such attacks.
Even with security envelope, since RIFT relies on Thrift encoders and
decoders generated automatically from IDL it is conceivable that
errors in such encoders/decoders could be discovered and lead to
delivery of corrupted packets or reception of packets that cannot be
decoded. Misformatted packets lead normally to decoder returning an
error condition to the caller and with that the packet is basically
unparsable with no other choice but to discard it. Should the
unlikely scenario occur of the decoder being forced to abort the
protocol this is neither better nor worse than today's behavior of
other protocols.
7.3. ZTP
Section 4.2.7 presents many attack vectors in untrusted environments,
starting with nodes that oscillate their level offers to the
possibility of nodes offering a ThreeWay adjacency with the highest
possible level value and a very long holdtime trying to put itself
"on top of the lattice" thereby allowing it to gain access to the
whole southbound topology. Session authentication mechanisms are
necessary in environments where this is possible and RIFT provides
the security envelope to ensure this if so desired.
7.4. Lifetime
Traditional IGP protocols are vulnerable to lifetime modification and
replay attacks that can be somewhat mitigated by using techniques
like [RFC7987]. RIFT removes this attack vector by protecting the
lifetime behind a signature computed over it and additional nonce
combination which makes even the replay attack window very small and
for practical purposes irrelevant since lifetime cannot be
artificially shortened by the attacker.
7.5. Packet Number
Optional packet number is carried in the security envelope without
any encryption protection and is hence vulnerable to replay and
modification attacks. Contrary to nonces this number must change on
every packet and would present a very high cryptographic load if
signed. The attack vector packet number present is relatively
benign. Changing the packet number by a man-in-the-middle attack
will only affect operational validation tools and possibly some
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performance optimizations on flooding. It is expected that an
implementation detecting too many "fake losses" or "misorderings" due
to the attack on the packet number would simply suppress its further
processing.
7.6. Outer Fingerprint Attacks
A node can try to inject LIE packets observing a conversation on the
wire by using the outer key ID albeit it cannot generate valid hashes
in case it changes the integrity of the message so the only possible
attack is DoS due to excessive LIE validation.
A node can try to replay previous LIEs with changed state that it
recorded but the attack is hard to replicate since the nonce
combination must match the ongoing exchange and is then limited to a
single flap only since both nodes will advance their nonces in case
the adjacency state changed. Even in the most unlikely case the
attack length is limited due to both sides periodically increasing
their nonces.
7.7. TIE Origin Fingerprint DoS Attacks
A compromised node can attempt to generate "fake TIEs" using other
nodes' TIE origin key identifiers. Albeit the ultimate validation of
the origin fingerprint will fail in such scenarios and not progress
further than immediately peering nodes, the resulting denial of
service attack seems unavoidable since the TIE origin key id is only
protected by the, here assumed to be compromised, node.
7.8. Host Implementations
It can be reasonably expected that with the proliferation of RotH
servers, rather than dedicated networking devices, will represent a
significant amount of RIFT devices. Given their normally far wider
software envelope and access granted to them, such servers are also
far more likely to be compromised and present an attack vector on the
protocol. Hijacking of prefixes to attract traffic is a trust
problem and cannot be easily addressed within the protocol if the
trust model is breached, i.e. the server presents valid credentials
to form an adjacency and issue TIEs. In an even more devious way,
the servers can present DoS (or even DDos) vectors of issuing too
many LIE packets, flood large amounts of North TIEs and attempt
similar resource overrun attacks. A prudent implementation forming
adjacencies to leaves should implement according thresholds
mechanisms and raise warnings when e.g. a leaf is advertising an
excess number of TIEs or prefixes. Additionally, such implementation
could refuse any topology information except the node's own TIEs and
authenticated, reflected South Node TIEs at own level.
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To isolate possible attack vectors on the leaf to the largest
possible extent a dedicated leaf-only implementation could run
without any configuration by hard-coding a well-known adjacency key
(which can be always rolled-over by the means of e.g. well-known key-
value distributed from top of the fabric), leaf level value and
always setting overload bit. All other values can be derived by
automatic means as described earlier in the protocol specification.
8. IANA Considerations
This specification requests multicast address assignments and
standard port numbers. Additionally registries for the schema are
requested and suggested values provided that reflect the numbers
allocated in the given schema.
8.1. Requested Multicast and Port Numbers
This document requests allocation in the 'IPv4 Multicast Address
Space' registry the suggested value of 224.0.0.120 as
'ALL_V4_RIFT_ROUTERS' and in the 'IPv6 Multicast Address Space'
registry the suggested value of FF02::A1F7 as 'ALL_V6_RIFT_ROUTERS'.
This document requests allocation in the 'Service Name and Transport
Protocol Port Number Registry' the allocation of a suggested value of
914 on udp for 'RIFT_LIES_PORT' and suggested value of 915 for
'RIFT_TIES_PORT'.
8.2. Requested Registries with Suggested Values
This section requests registries that help govern the schema via
usual IANA registry procedures. A top level 'RIFT' registry should
hold the according registries requested in the following sections
with their pre-defined values. IANA is requested to store the schema
version introducing the allocated value as well as, optionally, its
description when present. This will allow to assign different values
to an entry depending on schema version. Alternately, IANA is
requested to consider a root RIFT/3 registry to store RIFT schema
major version 3 values and may be requested in the future to create a
RIFT/4 registry under that. In any case, IANA is requested to store
the schema version in the entries since that will allow to
distinguish between minor versions in the same major schema version.
All values not suggested as to be considered `Unassigned`. The range
of every registry is a 16-bit integer. Allocation of new values is
always performed via `Expert Review` action.
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8.2.1. Registry RIFT_v5/common/AddressFamilyType"
Address family type.
8.2.1.1. Requested Entries
+=======================+=======+================+=============+
| Name | Value | Schema Version | Description |
+=======================+=======+================+=============+
| Illegal | 0 | 5.0 | |
+-----------------------+-------+----------------+-------------+
| AddressFamilyMinValue | 1 | 5.0 | |
+-----------------------+-------+----------------+-------------+
| IPv4 | 2 | 5.0 | |
+-----------------------+-------+----------------+-------------+
| IPv6 | 3 | 5.0 | |
+-----------------------+-------+----------------+-------------+
| AddressFamilyMaxValue | 4 | 5.0 | |
+-----------------------+-------+----------------+-------------+
Table 7
8.2.2. Registry RIFT_v5/common/HierarchyIndications"
Flags indicating node configuration in case of ZTP.
8.2.2.1. Requested Entries
+======================================+=====+========+=============+
| Name |Value| Schema| Description |
| | | Version| |
+======================================+=====+========+=============+
| leaf_only | 0| 5.0| |
+--------------------------------------+-----+--------+-------------+
| leaf_only_and_leaf_2_leaf_procedures | 1| 5.0| |
+--------------------------------------+-----+--------+-------------+
| top_of_fabric | 2| 5.0| |
+--------------------------------------+-----+--------+-------------+
Table 8
8.2.3. Registry RIFT_v5/common/IEEE802_1ASTimeStampType"
Timestamp per IEEE 802.1AS, all values MUST be interpreted in
implementation as unsigned.
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8.2.3.1. Requested Entries
+=========+=======+================+=============+
| Name | Value | Schema Version | Description |
+=========+=======+================+=============+
| AS_sec | 1 | 5.0 | |
+---------+-------+----------------+-------------+
| AS_nsec | 2 | 5.0 | |
+---------+-------+----------------+-------------+
Table 9
8.2.4. Registry RIFT_v5/common/IPAddressType"
IP address type.
8.2.4.1. Requested Entries
+=============+=======+================+=================+
| Name | Value | Schema Version | Description |
+=============+=======+================+=================+
| ipv4address | 1 | 5.0 | Content is IPv4 |
+-------------+-------+----------------+-----------------+
| ipv6address | 2 | 5.0 | Content is IPv6 |
+-------------+-------+----------------+-----------------+
Table 10
8.2.5. Registry RIFT_v5/common/IPPrefixType"
Prefix advertisement.
@note: for interface addresses the protocol can propagate the address
part beyond the subnet mask and on reachability computation that has
to be normalized. The non-significant bits can be used for
operational purposes.
8.2.5.1. Requested Entries
+============+=======+================+=============+
| Name | Value | Schema Version | Description |
+============+=======+================+=============+
| ipv4prefix | 1 | 5.0 | |
+------------+-------+----------------+-------------+
| ipv6prefix | 2 | 5.0 | |
+------------+-------+----------------+-------------+
Table 11
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8.2.6. Registry RIFT_v5/common/IPv4PrefixType"
IPv4 prefix type.
8.2.6.1. Requested Entries
+===========+=======+================+=============+
| Name | Value | Schema Version | Description |
+===========+=======+================+=============+
| address | 1 | 5.0 | |
+-----------+-------+----------------+-------------+
| prefixlen | 2 | 5.0 | |
+-----------+-------+----------------+-------------+
Table 12
8.2.7. Registry RIFT_v5/common/IPv6PrefixType"
IPv6 prefix type.
8.2.7.1. Requested Entries
+===========+=======+================+=============+
| Name | Value | Schema Version | Description |
+===========+=======+================+=============+
| address | 1 | 5.0 | |
+-----------+-------+----------------+-------------+
| prefixlen | 2 | 5.0 | |
+-----------+-------+----------------+-------------+
Table 13
8.2.8. Registry RIFT_v5/common/PrefixSequenceType"
Sequence of a prefix in case of move.
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8.2.8.1. Requested Entries
+===============+=======+=========+============================+
| Name | Value | Schema | Description |
| | | Version | |
+===============+=======+=========+============================+
| timestamp | 1 | 5.0 | |
+---------------+-------+---------+----------------------------+
| transactionid | 2 | 5.0 | Transaction ID set by |
| | | | client in e.g. in 6LoWPAN. |
+---------------+-------+---------+----------------------------+
Table 14
8.2.9. Registry RIFT_v5/common/RouteType"
RIFT route types. @note: The only purpose of those values is to
introduce an ordering whereas an implementation can choose internally
any other values as long the ordering is preserved
8.2.9.1. Requested Entries
+=====================+=======+================+=============+
| Name | Value | Schema Version | Description |
+=====================+=======+================+=============+
| Illegal | 0 | 5.0 | |
+---------------------+-------+----------------+-------------+
| RouteTypeMinValue | 1 | 5.0 | |
+---------------------+-------+----------------+-------------+
| Discard | 2 | 5.0 | |
+---------------------+-------+----------------+-------------+
| LocalPrefix | 3 | 5.0 | |
+---------------------+-------+----------------+-------------+
| SouthPGPPrefix | 4 | 5.0 | |
+---------------------+-------+----------------+-------------+
| NorthPGPPrefix | 5 | 5.0 | |
+---------------------+-------+----------------+-------------+
| NorthPrefix | 6 | 5.0 | |
+---------------------+-------+----------------+-------------+
| NorthExternalPrefix | 7 | 5.0 | |
+---------------------+-------+----------------+-------------+
| SouthPrefix | 8 | 5.0 | |
+---------------------+-------+----------------+-------------+
| SouthExternalPrefix | 9 | 5.0 | |
+---------------------+-------+----------------+-------------+
| NegativeSouthPrefix | 10 | 5.0 | |
+---------------------+-------+----------------+-------------+
| RouteTypeMaxValue | 11 | 5.0 | |
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+---------------------+-------+----------------+-------------+
Table 15
8.2.10. Registry RIFT_v5/common/TIETypeType"
Type of TIE.
8.2.10.1. Requested Entries
+===========================================+=====+=======+===========+
|Name |Value| Schema|Description|
| | |Version| |
+===========================================+=====+=======+===========+
|Illegal | 0| 5.0| |
+-------------------------------------------+-----+-------+-----------+
|TIETypeMinValue | 1| 5.0| |
+-------------------------------------------+-----+-------+-----------+
|NodeTIEType | 2| 5.0| |
+-------------------------------------------+-----+-------+-----------+
|PrefixTIEType | 3| 5.0| |
+-------------------------------------------+-----+-------+-----------+
|PositiveDisaggregationPrefixTIEType | 4| 5.0| |
+-------------------------------------------+-----+-------+-----------+
|NegativeDisaggregationPrefixTIEType | 5| 5.0| |
+-------------------------------------------+-----+-------+-----------+
|PGPrefixTIEType | 6| 5.0| |
+-------------------------------------------+-----+-------+-----------+
|KeyValueTIEType | 7| 5.0| |
+-------------------------------------------+-----+-------+-----------+
|ExternalPrefixTIEType | 8| 5.0| |
+-------------------------------------------+-----+-------+-----------+
|PositiveExternalDisaggregationPrefixTIEType| 9| 5.0| |
+-------------------------------------------+-----+-------+-----------+
|TIETypeMaxValue | 10| 5.0| |
+-------------------------------------------+-----+-------+-----------+
Table 16
8.2.11. Registry RIFT_v5/common/TieDirectionType"
Direction of TIEs.
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8.2.11.1. Requested Entries
+===================+=======+================+=============+
| Name | Value | Schema Version | Description |
+===================+=======+================+=============+
| Illegal | 0 | 5.0 | |
+-------------------+-------+----------------+-------------+
| South | 1 | 5.0 | |
+-------------------+-------+----------------+-------------+
| North | 2 | 5.0 | |
+-------------------+-------+----------------+-------------+
| DirectionMaxValue | 3 | 5.0 | |
+-------------------+-------+----------------+-------------+
Table 17
8.2.12. Registry RIFT_v5/encoding/Community"
Prefix community.
8.2.12.1. Requested Entries
+========+=======+================+===================+
| Name | Value | Schema Version | Description |
+========+=======+================+===================+
| top | 1 | 5.0 | Higher order bits |
+--------+-------+----------------+-------------------+
| bottom | 2 | 5.0 | Lower order bits |
+--------+-------+----------------+-------------------+
Table 18
8.2.13. Registry RIFT_v5/encoding/KeyValueTIEElement"
Generic key value pairs.
8.2.13.1. Requested Entries
+===========+=======+================+=============+
| Name | Value | Schema Version | Description |
+===========+=======+================+=============+
| keyvalues | 1 | 5.0 | |
+-----------+-------+----------------+-------------+
Table 19
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8.2.14. Registry RIFT_v5/encoding/LIEPacket"
RIFT LIE Packet.
@note: this node's level is already included on the packet header
8.2.14.1. Requested Entries
+=============================+=======+=========+=================+
| Name | Value | Schema | Description |
| | | Version | |
+=============================+=======+=========+=================+
| name | 1 | 5.0 | Node or |
| | | | adjacency name. |
+-----------------------------+-------+---------+-----------------+
| local_id | 2 | 5.0 | Local link ID. |
+-----------------------------+-------+---------+-----------------+
| flood_port | 3 | 5.0 | UDP port to |
| | | | which we can |
| | | | receive flooded |
| | | | TIEs. |
+-----------------------------+-------+---------+-----------------+
| link_mtu_size | 4 | 5.0 | Layer 3 MTU, |
| | | | used to |
| | | | discover |
| | | | mismatch. |
+-----------------------------+-------+---------+-----------------+
| link_bandwidth | 5 | 5.0 | Local link |
| | | | bandwidth on |
| | | | the interface. |
+-----------------------------+-------+---------+-----------------+
| neighbor | 6 | 5.0 | Reflects the |
| | | | neighbor once |
| | | | received to |
| | | | provide 3-way |
| | | | connectivity. |
+-----------------------------+-------+---------+-----------------+
| pod | 7 | 5.0 | Node's PoD. |
+-----------------------------+-------+---------+-----------------+
| node_capabilities | 10 | 5.0 | Node |
| | | | capabilities |
| | | | supported. |
+-----------------------------+-------+---------+-----------------+
| link_capabilities | 11 | 5.0 | Capabilities of |
| | | | this link. |
+-----------------------------+-------+---------+-----------------+
| holdtime | 12 | 5.0 | Required |
| | | | holdtime of the |
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| | | | adjacency, i.e. |
| | | | for how long a |
| | | | period should |
| | | | adjacency be |
| | | | kept up without |
| | | | valid LIE |
| | | | reception. |
+-----------------------------+-------+---------+-----------------+
| label | 13 | 5.0 | Optional, |
| | | | unsolicited, |
| | | | downstream |
| | | | assigned |
| | | | locally |
| | | | significant |
| | | | label value for |
| | | | the adjacency. |
+-----------------------------+-------+---------+-----------------+
| not_a_ztp_offer | 21 | 5.0 | Indicates that |
| | | | the level on |
| | | | the LIE must |
| | | | not be used to |
| | | | derive a ZTP |
| | | | level by the |
| | | | receiving node. |
+-----------------------------+-------+---------+-----------------+
| you_are_flood_repeater | 22 | 5.0 | Indicates to |
| | | | northbound |
| | | | neighbor that |
| | | | it should be |
| | | | reflooding TIEs |
| | | | received from |
| | | | this node to |
| | | | achieve flood |
| | | | reduction and |
| | | | balancing for |
| | | | northbound |
| | | | flooding. |
+-----------------------------+-------+---------+-----------------+
| you_are_sending_too_quickly | 23 | 5.0 | Indicates to |
| | | | neighbor to |
| | | | flood node TIEs |
| | | | only and slow |
| | | | down all other |
| | | | TIEs. Ignored |
| | | | when received |
| | | | from southbound |
| | | | neighbor. |
+-----------------------------+-------+---------+-----------------+
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| instance_name | 24 | 5.0 | Instance name |
| | | | in case |
| | | | multiple RIFT |
| | | | instances |
| | | | running on same |
| | | | interface. |
+-----------------------------+-------+---------+-----------------+
Table 20
8.2.15. Registry RIFT_v5/encoding/LinkCapabilities"
Link capabilities.
8.2.15.1. Requested Entries
+=========================+=======+=========+===================+
| Name | Value | Schema | Description |
| | | Version | |
+=========================+=======+=========+===================+
| bfd | 1 | 5.0 | Indicates that |
| | | | the link is |
| | | | supporting BFD. |
+-------------------------+-------+---------+-------------------+
| ipv4_forwarding_capable | 2 | 5.0 | Indicates whether |
| | | | the interface |
| | | | will support IPv4 |
| | | | forwarding. |
+-------------------------+-------+---------+-------------------+
Table 21
8.2.16. Registry RIFT_v5/encoding/LinkIDPair"
LinkID pair describes one of parallel links between two nodes.
8.2.16.1. Requested Entries
+============================+=======+=========+====================+
| Name | Value | Schema | Description |
| | | Version | |
+============================+=======+=========+====================+
| local_id | 1 | 5.0 | Node-wide unique |
| | | | value for the |
| | | | local link. |
+----------------------------+-------+---------+--------------------+
| remote_id | 2 | 5.0 | Received remote |
| | | | link ID for this |
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| | | | link. |
+----------------------------+-------+---------+--------------------+
| platform_interface_index | 10 | 5.0 | Describes the |
| | | | local interface |
| | | | index of the |
| | | | link. |
+----------------------------+-------+---------+--------------------+
| platform_interface_name | 11 | 5.0 | Describes the |
| | | | local interface |
| | | | name. |
+----------------------------+-------+---------+--------------------+
| trusted_outer_security_key | 12 | 5.0 | Indicates |
| | | | whether the link |
| | | | is secured, i.e. |
| | | | protected by |
| | | | outer key, |
| | | | absence of this |
| | | | element means no |
| | | | indication, |
| | | | undefined outer |
| | | | key means not |
| | | | secured. |
+----------------------------+-------+---------+--------------------+
| bfd_up | 13 | 5.0 | Indicates |
| | | | whether the link |
| | | | is protected by |
| | | | established BFD |
| | | | session. |
+----------------------------+-------+---------+--------------------+
| address_families | 14 | 5.0 | Optional |
| | | | indication which |
| | | | address families |
| | | | are up on the |
| | | | interface |
+----------------------------+-------+---------+--------------------+
Table 22
8.2.17. Registry RIFT_v5/encoding/Neighbor"
Neighbor structure.
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8.2.17.1. Requested Entries
+============+=======+================+===================+
| Name | Value | Schema Version | Description |
+============+=======+================+===================+
| originator | 1 | 5.0 | System ID of the |
| | | | originator. |
+------------+-------+----------------+-------------------+
| remote_id | 2 | 5.0 | ID of remote side |
| | | | of the link. |
+------------+-------+----------------+-------------------+
Table 23
8.2.18. Registry RIFT_v5/encoding/NodeCapabilities"
Capabilities the node supports.
8.2.18.1. Requested Entries
+========================+=======+=========+======================+
| Name | Value | Schema | Description |
| | | Version | |
+========================+=======+=========+======================+
| protocol_minor_version | 1 | 5.0 | Must advertise |
| | | | supported minor |
| | | | version dialect that |
| | | | way. |
+------------------------+-------+---------+----------------------+
| flood_reduction | 2 | 5.0 | indicates that node |
| | | | supports flood |
| | | | reduction. |
+------------------------+-------+---------+----------------------+
| hierarchy_indications | 3 | 5.0 | indicates place in |
| | | | hierarchy, i.e. top- |
| | | | of-fabric or leaf |
| | | | only (in ZTP) or |
| | | | support for leaf- |
| | | | 2-leaf procedures. |
+------------------------+-------+---------+----------------------+
Table 24
8.2.19. Registry RIFT_v5/encoding/NodeFlags"
Indication flags of the node.
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8.2.19.1. Requested Entries
+==========+=======+=========+=====================================+
| Name | Value | Schema | Description |
| | | Version | |
+==========+=======+=========+=====================================+
| overload | 1 | 5.0 | Indicates that node is in overload, |
| | | | do not transit traffic through it. |
+----------+-------+---------+-------------------------------------+
Table 25
8.2.20. Registry RIFT_v5/encoding/NodeNeighborsTIEElement"
neighbor of a node
8.2.20.1. Requested Entries
+===========+=======+=========+====================================+
| Name | Value | Schema | Description |
| | | Version | |
+===========+=======+=========+====================================+
| level | 1 | 5.0 | level of neighbor |
+-----------+-------+---------+------------------------------------+
| cost | 3 | 5.0 | Cost to neighbor. Ignore anything |
| | | | larger than `infinite_distance` |
| | | | and `invalid_distance` |
+-----------+-------+---------+------------------------------------+
| link_ids | 4 | 5.0 | can carry description of multiple |
| | | | parallel links in a TIE |
+-----------+-------+---------+------------------------------------+
| bandwidth | 5 | 5.0 | total bandwith to neighbor as sum |
| | | | of all parallel links |
+-----------+-------+---------+------------------------------------+
Table 26
8.2.21. Registry RIFT_v5/encoding/NodeTIEElement"
Description of a node.
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8.2.21.1. Requested Entries
+=================+=======+=========+=============================+
| Name | Value | Schema | Description |
| | | Version | |
+=================+=======+=========+=============================+
| level | 1 | 5.0 | Level of the node. |
+-----------------+-------+---------+-----------------------------+
| neighbors | 2 | 5.0 | Node's neighbors. Multiple |
| | | | node TIEs can carry |
| | | | disjoint sets of neighbors. |
+-----------------+-------+---------+-----------------------------+
| capabilities | 3 | 5.0 | Capabilities of the node. |
+-----------------+-------+---------+-----------------------------+
| flags | 4 | 5.0 | Flags of the node. |
+-----------------+-------+---------+-----------------------------+
| name | 5 | 5.0 | Optional node name for |
| | | | easier operations. |
+-----------------+-------+---------+-----------------------------+
| pod | 6 | 5.0 | PoD to which the node |
| | | | belongs. |
+-----------------+-------+---------+-----------------------------+
| startup_time | 7 | 5.0 | optional startup time of |
| | | | the node |
+-----------------+-------+---------+-----------------------------+
| miscabled_links | 10 | 5.0 | If any local links are |
| | | | miscabled, this indication |
| | | | is flooded. |
+-----------------+-------+---------+-----------------------------+
Table 27
8.2.22. Registry RIFT_v5/encoding/PacketContent"
Content of a RIFT packet.
8.2.22.1. Requested Entries
+======+=======+================+=============+
| Name | Value | Schema Version | Description |
+======+=======+================+=============+
| lie | 1 | 5.0 | |
+------+-------+----------------+-------------+
| tide | 2 | 5.0 | |
+------+-------+----------------+-------------+
| tire | 3 | 5.0 | |
+------+-------+----------------+-------------+
| tie | 4 | 5.0 | |
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+------+-------+----------------+-------------+
Table 28
8.2.23. Registry RIFT_v5/encoding/PacketHeader"
Common RIFT packet header.
8.2.23.1. Requested Entries
+===============+=======+=========+===============================+
| Name | Value | Schema | Description |
| | | Version | |
+===============+=======+=========+===============================+
| major_version | 1 | 5.0 | Major version of protocol. |
+---------------+-------+---------+-------------------------------+
| minor_version | 2 | 5.0 | Minor version of protocol. |
+---------------+-------+---------+-------------------------------+
| sender | 3 | 5.0 | Node sending the packet, in |
| | | | case of LIE/TIRE/TIDE also |
| | | | the originator of it. |
+---------------+-------+---------+-------------------------------+
| level | 4 | 5.0 | Level of the node sending the |
| | | | packet, required on |
| | | | everything except LIEs. Lack |
| | | | of presence on LIEs indicates |
| | | | UNDEFINED_LEVEL and is used |
| | | | in ZTP procedures. |
+---------------+-------+---------+-------------------------------+
Table 29
8.2.24. Registry RIFT_v5/encoding/PrefixAttributes"
Attributes of a prefix.
8.2.24.1. Requested Entries
+===================+=======+=========+========================+
| Name | Value | Schema | Description |
| | | Version | |
+===================+=======+=========+========================+
| metric | 2 | 5.0 | Distance of the |
| | | | prefix. |
+-------------------+-------+---------+------------------------+
| tags | 3 | 5.0 | Generic unordered set |
| | | | of route tags, can be |
| | | | redistributed to other |
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| | | | protocols or use |
| | | | within the context of |
| | | | real time analytics. |
+-------------------+-------+---------+------------------------+
| monotonic_clock | 4 | 5.0 | Monotonic clock for |
| | | | mobile addresses. |
+-------------------+-------+---------+------------------------+
| loopback | 6 | 5.0 | Indicates if the |
| | | | prefix is a node |
| | | | loopback. |
+-------------------+-------+---------+------------------------+
| directly_attached | 7 | 5.0 | Indicates that the |
| | | | prefix is directly |
| | | | attached. |
+-------------------+-------+---------+------------------------+
| from_link | 10 | 5.0 | link to which the |
| | | | address belongs to. |
+-------------------+-------+---------+------------------------+
Table 30
8.2.25. Registry RIFT_v5/encoding/PrefixTIEElement"
TIE carrying prefixes
8.2.25.1. Requested Entries
+==========+=======+================+========================+
| Name | Value | Schema Version | Description |
+==========+=======+================+========================+
| prefixes | 1 | 5.0 | Prefixes with the |
| | | | associated attributes. |
+----------+-------+----------------+------------------------+
Table 31
8.2.26. Registry RIFT_v5/encoding/ProtocolPacket"
RIFT packet structure.
8.2.26.1. Requested Entries
+=========+=======+================+=============+
| Name | Value | Schema Version | Description |
+=========+=======+================+=============+
| header | 1 | 5.0 | |
+---------+-------+----------------+-------------+
| content | 2 | 5.0 | |
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+---------+-------+----------------+-------------+
Table 32
8.2.27. Registry RIFT_v5/encoding/TIDEPacket"
TIDE with *sorted* TIE headers.
8.2.27.1. Requested Entries
+=============+=======+================+=====================+
| Name | Value | Schema Version | Description |
+=============+=======+================+=====================+
| start_range | 1 | 5.0 | First TIE header in |
| | | | the tide packet. |
+-------------+-------+----------------+---------------------+
| end_range | 2 | 5.0 | Last TIE header in |
| | | | the tide packet. |
+-------------+-------+----------------+---------------------+
| headers | 3 | 5.0 | _Sorted_ list of |
| | | | headers. |
+-------------+-------+----------------+---------------------+
Table 33
8.2.28. Registry RIFT_v5/encoding/TIEElement"
Single element in a TIE.
8.2.28.1. Requested Entries
+=========================================+=====+=======+=================================+
|Name |Value| Schema|Description |
| | |Version| |
+=========================================+=====+=======+=================================+
|node | 1| 5.0| Used in case of enum|
| | | | common.TIETypeType.NodeTIEType.|
+-----------------------------------------+-----+-------+---------------------------------+
|prefixes | 2| 5.0| Used in case of enum|
| | | |common.TIETypeType.PrefixTIEType.|
+-----------------------------------------+-----+-------+---------------------------------+
|positive_disaggregation_prefixes | 3| 5.0| Positive prefixes (always|
| | | | southbound).|
+-----------------------------------------+-----+-------+---------------------------------+
|negative_disaggregation_prefixes | 5| 5.0| Transitive, negative prefixes|
| | | | (always southbound)|
+-----------------------------------------+-----+-------+---------------------------------+
|external_prefixes | 6| 5.0| Externally reimported prefixes.|
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+-----------------------------------------+-----+-------+---------------------------------+
|positive_external_disaggregation_prefixes| 7| 5.0| Positive external disaggregated|
| | | | prefixes (always southbound).|
+-----------------------------------------+-----+-------+---------------------------------+
|keyvalues | 9| 5.0| Key-Value store elements.|
+-----------------------------------------+-----+-------+---------------------------------+
Table 34
8.2.29. Registry RIFT_v5/encoding/TIEHeader"
Header of a TIE.
8.2.29.1. Requested Entries
+======================+=======+=========+=========================+
| Name | Value | Schema | Description |
| | | Version | |
+======================+=======+=========+=========================+
| tieid | 2 | 5.0 | ID of the tie. |
+----------------------+-------+---------+-------------------------+
| seq_nr | 3 | 5.0 | Sequence number of the |
| | | | tie. |
+----------------------+-------+---------+-------------------------+
| origination_time | 10 | 5.0 | Absolute timestamp when |
| | | | the TIE was generated. |
+----------------------+-------+---------+-------------------------+
| origination_lifetime | 12 | 5.0 | Original lifetime when |
| | | | the TIE was generated. |
+----------------------+-------+---------+-------------------------+
Table 35
8.2.30. Registry RIFT_v5/encoding/TIEHeaderWithLifeTime"
Header of a TIE as described in TIRE/TIDE.
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8.2.30.1. Requested Entries
+====================+=======+================+=====================+
| Name | Value | Schema Version | Description |
+====================+=======+================+=====================+
| header | 1 | 5.0 | |
+--------------------+-------+----------------+---------------------+
| remaining_lifetime | 2 | 5.0 | Remaining |
| | | | lifetime. |
+--------------------+-------+----------------+---------------------+
Table 36
8.2.31. Registry RIFT_v5/encoding/TIEID"
Unique ID of a TIE.
8.2.31.1. Requested Entries
+============+=======+================+======================+
| Name | Value | Schema Version | Description |
+============+=======+================+======================+
| direction | 1 | 5.0 | direction of TIE |
+------------+-------+----------------+----------------------+
| originator | 2 | 5.0 | indicates originator |
| | | | of the TIE |
+------------+-------+----------------+----------------------+
| tietype | 3 | 5.0 | type of the tie |
+------------+-------+----------------+----------------------+
| tie_nr | 4 | 5.0 | number of the tie |
+------------+-------+----------------+----------------------+
Table 37
8.2.32. Registry RIFT_v5/encoding/TIEPacket"
TIE packet
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8.2.32.1. Requested Entries
+=========+=======+================+=============+
| Name | Value | Schema Version | Description |
+=========+=======+================+=============+
| header | 1 | 5.0 | |
+---------+-------+----------------+-------------+
| element | 2 | 5.0 | |
+---------+-------+----------------+-------------+
Table 38
8.2.33. Registry RIFT_v5/encoding/TIREPacket"
TIRE packet
8.2.33.1. Requested Entries
+=========+=======+================+=============+
| Name | Value | Schema Version | Description |
+=========+=======+================+=============+
| headers | 1 | 5.0 | |
+---------+-------+----------------+-------------+
Table 39
9. Acknowledgments
A new routing protocol in its complexity is not a product of a parent
but of a village as the author list shows already. However, many
more people provided input, fine-combed the specification based on
their experience in design, implementation or application of
protocols in IP fabrics. This section will make an inadequate
attempt in recording their contribution.
Many thanks to Naiming Shen for some of the early discussions around
the topic of using IGPs for routing in topologies related to Clos.
Russ White to be especially acknowledged for the key conversation on
epistemology that allowed to tie current asynchronous distributed
systems theory results to a modern protocol design presented in this
scope. Adrian Farrel, Joel Halpern, Jeffrey Zhang, Krzysztof
Szarkowicz, Nagendra Kumar, Melchior Aelmans, Kaushal Tank, Will
Jones, Moin Ahmed, Sandy Zhang and Jordan Head (in no particular
order) provided thoughtful comments that improved the readability of
the document and found good amount of corners where the light failed
to shine. Kris Price was first to mention single router, single arm
default considerations. Jeff Tantsura helped out with some initial
thoughts on BFD interactions while Jeff Haas corrected several
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misconceptions about BFD's finer points and helped to improve the
security section around leaf considerations. Artur Makutunowicz
pointed out many possible improvements and acted as sounding board in
regard to modern protocol implementation techniques RIFT is
exploring. Barak Gafni formalized first time clearly the problem of
partitioned spine and fallen leaves on a (clean) napkin in Singapore
that led to the very important part of the specification centered
around multiple Top-of-Fabric planes and negative disaggregation.
Igor Gashinsky and others shared many thoughts on problems
encountered in design and operation of large-scale data center
fabrics. Xu Benchong found a delicate error in the flooding
procedures and a schema datatype size mismatch.
Last but not least, Alvaro Retana guided the undertaking by asking
many necessary procedural and technical questions which did not only
improve the content but did also lay out the track towards
publication.
10. Contributors
This work is a product of a list of individuals which are all to be
considered major contributors independent of the fact whether their
name made it to the limited boilerplate author's list or not.
+======================+===+================+===+==================+
+======================+===+================+===+==================+
| Tony Przygienda, Ed. | | | Alankar Sharma | | | Pascal Thubert |
+----------------------+---+----------------+---+------------------+
| Juniper | | | Comcast | | | Cisco |
+----------------------+---+----------------+---+------------------+
| Bruno Rijsman | | | Jordan Head | | | Dmitry Afanasiev |
+----------------------+---+----------------+---+------------------+
| Individual | | | Juniper | | | Yandex |
+----------------------+---+----------------+---+------------------+
| Don Fedyk | | | Alia Atlas | | | John Drake |
+----------------------+---+----------------+---+------------------+
| Individual | | | Individual | | | Juniper |
+----------------------+---+----------------+---+------------------+
| Ilya Vershkov | | | | | | | | |
+----------------------+---+----------------+---+------------------+
| Mellanox | | | | | | | | |
+----------------------+---+----------------+---+------------------+
Table 40: RIFT Authors
11. References
11.1. Normative References
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[EUI64] IEEE, "Guidelines for Use of Extended Unique Identifier
(EUI), Organizationally Unique Identifier (OUI), and
Company ID (CID)", IEEE EUI,
<http://standards.ieee.org/develop/regauth/tut/eui.pdf>.
[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
DOI 10.17487/RFC1982, August 1996,
<https://www.rfc-editor.org/info/rfc1982>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23,
RFC 2365, DOI 10.17487/RFC2365, July 1998,
<https://www.rfc-editor.org/info/rfc2365>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
<https://www.rfc-editor.org/info/rfc5082>.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>.
[RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
Authentication", RFC 5709, DOI 10.17487/RFC5709, October
2009, <https://www.rfc-editor.org/info/rfc5709>.
[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
DOI 10.17487/RFC5881, June 2010,
<https://www.rfc-editor.org/info/rfc5881>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
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[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
DOI 10.17487/RFC6830, January 2013,
<https://www.rfc-editor.org/info/rfc6830>.
[RFC7987] Ginsberg, L., Wells, P., Decraene, B., Przygienda, T., and
H. Gredler, "IS-IS Minimum Remaining Lifetime", RFC 7987,
DOI 10.17487/RFC7987, October 2016,
<https://www.rfc-editor.org/info/rfc7987>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8202] Ginsberg, L., Previdi, S., and W. Henderickx, "IS-IS
Multi-Instance", RFC 8202, DOI 10.17487/RFC8202, June
2017, <https://www.rfc-editor.org/info/rfc8202>.
[RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C.
Perkins, "Registration Extensions for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Neighbor
Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018,
<https://www.rfc-editor.org/info/rfc8505>.
[thrift] Apache Software Foundation, "Thrift Interface Description
Language", <https://thrift.apache.org/docs/idl>.
[VFR] Erlebach et al., T., "Cuts and Disjoint Paths in the
Valley-Free Path Model of Internet BGP Routing", Springer
Berlin Heidelberg Combinatorial and Algorithmic Aspects of
Networking, 2005.
11.2. Informative References
[APPLICABILITY]
Wei, Y., Zhang, Z., Afanasiev, D., Thubert, P., Verhaeg,
T., and J. Kowalczyk, "RIFT Applicability", Work in
Progress, Internet-Draft, draft-ietf-rift-applicability-
05, 26 April 2021, <https://datatracker.ietf.org/doc/html/
draft-ietf-rift-applicability-05>.
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[CLOS] Yuan, X., "On Nonblocking Folded-Clos Networks in Computer
Communication Environments", IEEE International Parallel &
Distributed Processing Symposium, 2011.
[DIJKSTRA] Dijkstra, E. W., "A Note on Two Problems in Connexion with
Graphs", Journal Numer. Math. , 1959.
[DYNAMO] De Candia et al., G., "Dynamo: amazon's highly available
key-value store", ACM SIGOPS symposium on Operating
systems principles (SOSP '07), 2007.
[EPPSTEIN] Eppstein, D., "Finding the k-Shortest Paths", 1997.
[FATTREE] Leiserson, C. E., "Fat-Trees: Universal Networks for
Hardware-Efficient Supercomputing", 1985.
[IEEEstd1588]
IEEE, "IEEE Standard for a Precision Clock Synchronization
Protocol for Networked Measurement and Control Systems",
IEEE Standard 1588,
<https://ieeexplore.ieee.org/document/4579760/>.
[IEEEstd8021AS]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks - Timing and Synchronization for Time-Sensitive
Applications in Bridged Local Area Networks",
IEEE Standard 802.1AS,
<https://ieeexplore.ieee.org/document/5741898/>.
[RFC0826] Plummer, D., "An Ethernet Address Resolution Protocol: Or
Converting Network Protocol Addresses to 48.bit Ethernet
Address for Transmission on Ethernet Hardware", STD 37,
RFC 826, DOI 10.17487/RFC0826, November 1982,
<https://www.rfc-editor.org/info/rfc826>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
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[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
[VAHDAT08] Al-Fares, M., Loukissas, A., and A. Vahdat, "A Scalable,
Commodity Data Center Network Architecture", SIGCOMM ,
2008.
[Wikipedia]
Wikipedia,
"https://en.wikipedia.org/wiki/Serial_number_arithmetic",
2016.
Appendix A. Sequence Number Binary Arithmetic
The only reasonably reference to a cleaner than [RFC1982] sequence
number solution is given in [Wikipedia]. It basically converts the
problem into two complement's arithmetic. Assuming a straight two
complement's subtractions on the bit-width of the sequence number the
according >: and =: relations are defined as:
U_1, U_2 are 12-bits aligned unsigned version number
D_f is ( U_1 - U_2 ) interpreted as two complement signed 12-bits
D_b is ( U_2 - U_1 ) interpreted as two complement signed 12-bits
U_1 >: U_2 IIF D_f > 0 *and* D_b < 0
U_1 =: U_2 IIF D_f = 0
The >: relationship is anti-symmetric but not transitive. Observe
that this leaves >: of the numbers having maximum two complement
distance, e.g. ( 0 and 0x800 ) undefined in the 12-bits case since
D_f and D_b are both -0x7ff.
A simple example of the relationship in case of 3-bit arithmetic
follows as table indicating D_f/D_b values and then the relationship
of U_1 to U_2:
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U2 / U1 0 1 2 3 4 5 6 7
0 +/+ +/- +/- +/- -/- -/+ -/+ -/+
1 -/+ +/+ +/- +/- +/- -/- -/+ -/+
2 -/+ -/+ +/+ +/- +/- +/- -/- -/+
3 -/+ -/+ -/+ +/+ +/- +/- +/- -/-
4 -/- -/+ -/+ -/+ +/+ +/- +/- +/-
5 +/- -/- -/+ -/+ -/+ +/+ +/- +/-
6 +/- +/- -/- -/+ -/+ -/+ +/+ +/-
7 +/- +/- +/- -/- -/+ -/+ -/+ +/+
U2 / U1 0 1 2 3 4 5 6 7
0 = > > > ? < < <
1 < = > > > ? < <
2 < < = > > > ? <
3 < < < = > > > ?
4 ? < < < = > > >
5 > ? < < < = > >
6 > > ? < < < = >
7 > > > ? < < < =
Appendix B. Information Elements Schema
This section introduces the schema for information elements. The IDL
is Thrift [thrift].
On schema changes that
1. change field numbers *or*
2. add new *required* fields *or*
3. remove any fields *or*
4. change lists into sets, unions into structures *or*
5. change multiplicity of fields *or*
6. changes name of any field or type *or*
7. change data types of any field *or*
8. adds, changes or removes a default value of any *existing* field
*or*
9. removes or changes any defined constant or constant value *or*
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10. changes any enumeration type except extending
`common.TIETypeType` (use of enumeration types is generally
discouraged) *or*
11. add new TIE type to `TIETypeType` with flooding scope different
from prefix TIE flooding scope
major version of the schema MUST increase. All other changes MUST
increase minor version within the same major.
Introducing an optional field does not cause a major version increase
even if the fields inside the structure are optional with defaults.
All signed integer as forced by Thrift [thrift] support must be cast
for internal purposes to equivalent unsigned values without
discarding the signedness bit. An implementation SHOULD try to avoid
using the signedness bit when generating values.
The schema is normative.
B.1. Backwards-Compatible Extension of Schema
The set of rules in Appendix B guarantees that every decoder can
process serialized content generated by a higher minor version of the
schema and with that the protocol can progress without a 'fork-lift'.
Contrary to that, content serialized using a major version X is *not*
expected to be decodable by any implementation using decoder for a
model with a major version lower than X.
Additionally, based on the propagated minor version in encoded
content and added optional node capabilities new TIE types or even
de-facto mandatory fields can be introduced without progressing the
major version albeit only nodes supporting such new extensions would
decode them. Given the model is encoded at the source and never re-
encoded flooding through nodes not understanding any new extensions
will preserve the according fields. However, it is important to
understand that a higher minor version of a schema does *not*
guarantee that capabilities introduced in lower minors of the same
major are supported. The `node_capabilities` field is used to
indicate which capabilities are supported.
Specifically, the schema may add elements to `NodeCapabilities` field
future capabilities to indicate whether it will support
interpretation of schema extensions on the same major revision. Such
fields MUST be optional and have an implicit or explicit false
default value. If a future capability changes route selection or
generates blackholes if some nodes are not supporting it then a major
version increment will be however unavoidable. `NodeCapabilities`
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shown in LIE MUST match the capabilities shown in the Node TIEs,
otherwise the behavior is unspecified. A node detecting the mismatch
SHOULD generate a notification.
To support new TIE types without increasing the major version
enumeration `TIEElement` can be extended with new optional elements
for new `common.TIETypeType` values as long the scope of the new TIE
matches the prefix TIE scope. In case it is necessary to understand
whether all nodes can parse the new TIE type a node capability MUST
be added in `NodeCapabilities` to prevent a non-homogenous network.
B.2. common.thrift
/**
Thrift file with common definitions for RIFT
*/
namespace py common
/** @note MUST be interpreted in implementation as unsigned 64 bits.
*/
typedef i64 SystemIDType
typedef i32 IPv4Address
/** this has to be long enough to accomodate prefix */
typedef binary IPv6Address
/** @note MUST be interpreted in implementation as unsigned */
typedef i16 UDPPortType
/** @note MUST be interpreted in implementation as unsigned */
typedef i32 TIENrType
/** @note MUST be interpreted in implementation as unsigned */
typedef i32 MTUSizeType
/** @note MUST be interpreted in implementation as unsigned
rolling over number */
typedef i64 SeqNrType
/** @note MUST be interpreted in implementation as unsigned */
typedef i32 LifeTimeInSecType
/** @note MUST be interpreted in implementation as unsigned */
typedef i8 LevelType
typedef i16 PacketNumberType
/** @note MUST be interpreted in implementation as unsigned */
typedef i32 PodType
/** @note MUST be interpreted in implementation as unsigned.
This is carried in the
security envelope and must hence fit into 8 bits. */
typedef i8 VersionType
/** @note MUST be interpreted in implementation as unsigned */
typedef i16 MinorVersionType
/** @note MUST be interpreted in implementation as unsigned */
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typedef i32 MetricType
/** @note MUST be interpreted in implementation as unsigned
and unstructured */
typedef i64 RouteTagType
/** @note MUST be interpreted in implementation as unstructured
label value */
typedef i32 LabelType
/** @note MUST be interpreted in implementation as unsigned */
typedef i32 BandwithInMegaBitsType
/** @note Key Value key ID type */
typedef i32 KeyIDType
/** node local, unique identification for a link (interface/tunnel
* etc. Basically anything RIFT runs on). This is kept
* at 32 bits so it aligns with BFD [RFC5880] discriminator size.
*/
typedef i32 LinkIDType
/** @note MUST be interpreted in implementation as unsigned,
especially since we have the /128 IPv6 case. */
typedef i8 PrefixLenType
/** timestamp in seconds since the epoch */
typedef i64 TimestampInSecsType
/** security nonce.
@note MUST be interpreted in implementation as rolling
over unsigned value */
typedef i16 NonceType
/** LIE FSM holdtime type */
typedef i16 TimeIntervalInSecType
/** Transaction ID type for prefix mobility as specified by RFC6550,
value MUST be interpreted in implementation as unsigned */
typedef i8 PrefixTransactionIDType
/** Timestamp per IEEE 802.1AS, all values MUST be interpreted in
implementation as unsigned. */
struct IEEE802_1ASTimeStampType {
1: required i64 AS_sec;
2: optional i32 AS_nsec;
}
/** generic counter type */
typedef i64 CounterType
/** Platform Interface Index type, i.e. index of interface on hardware,
can be used e.g. with RFC5837 */
typedef i32 PlatformInterfaceIndex
/** Flags indicating node configuration in case of ZTP.
*/
enum HierarchyIndications {
/** forces level to `leaf_level` and enables according procedures */
leaf_only = 0,
/** forces level to `leaf_level` and enables according procedures */
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leaf_only_and_leaf_2_leaf_procedures = 1,
/** forces level to `top_of_fabric` and enables according
procedures */
top_of_fabric = 2,
}
const PacketNumberType undefined_packet_number = 0
/** used when node is configured as top of fabric in ZTP.*/
const LevelType top_of_fabric_level = 24
/** default bandwidth on a link */
const BandwithInMegaBitsType default_bandwidth = 100
/** fixed leaf level when ZTP is not used */
const LevelType leaf_level = 0
const LevelType default_level = leaf_level
const PodType default_pod = 0
const LinkIDType undefined_linkid = 0
/** invalid key for key value */
const KeyIDType invalid_key_value_key = 0
/** default distance used */
const MetricType default_distance = 1
/** any distance larger than this will be considered infinity */
const MetricType infinite_distance = 0x7FFFFFFF
/** represents invalid distance */
const MetricType invalid_distance = 0
const bool overload_default = false
const bool flood_reduction_default = true
/** default LIE FSM LIE TX internval time */
const TimeIntervalInSecType default_lie_tx_interval = 1
/** default LIE FSM holddown time */
const TimeIntervalInSecType default_lie_holdtime = 3
/** multipler for default_lie_holdtime to hold down multiple neighbors */
const i8 multiple_neighbors_lie_holdtime_multipler = 4
/** default ZTP FSM holddown time */
const TimeIntervalInSecType default_ztp_holdtime = 1
/** by default LIE levels are ZTP offers */
const bool default_not_a_ztp_offer = false
/** by default everyone is repeating flooding */
const bool default_you_are_flood_repeater = true
/** 0 is illegal for SystemID */
const SystemIDType IllegalSystemID = 0
/** empty set of nodes */
const set<SystemIDType> empty_set_of_nodeids = {}
/** default lifetime of TIE is one week */
const LifeTimeInSecType default_lifetime = 604800
/** default lifetime when TIEs are purged is 5 minutes */
const LifeTimeInSecType purge_lifetime = 300
/** optional round down interval when TIEs are sent with security hashes
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to prevent excessive computation. **/
const LifeTimeInSecType rounddown_lifetime_interval = 60
/** any `TieHeader` that has a smaller lifetime difference
than this constant is equal (if other fields equal). */
const LifeTimeInSecType lifetime_diff2ignore = 400
/** default UDP port to run LIEs on */
const UDPPortType default_lie_udp_port = 914
/** default UDP port to receive TIEs on, that can be peer specific */
const UDPPortType default_tie_udp_flood_port = 915
/** default MTU link size to use */
const MTUSizeType default_mtu_size = 1400
/** default link being BFD capable */
const bool bfd_default = true
/** undefined nonce, equivalent to missing nonce */
const NonceType undefined_nonce = 0;
/** outer security key id, MUST be interpreted as in implementation
as unsigned */
typedef i8 OuterSecurityKeyID
/** security key id, MUST be interpreted as in implementation
as unsigned */
typedef i32 TIESecurityKeyID
/** undefined key */
const TIESecurityKeyID undefined_securitykey_id = 0;
/** Maximum delta (negative or positive) that a mirrored nonce can
deviate from local value to be considered valid. */
const i16 maximum_valid_nonce_delta = 5;
const TimeIntervalInSecType nonce_regeneration_interval = 300;
/** Direction of TIEs. */
enum TieDirectionType {
Illegal = 0,
South = 1,
North = 2,
DirectionMaxValue = 3,
}
/** Address family type. */
enum AddressFamilyType {
Illegal = 0,
AddressFamilyMinValue = 1,
IPv4 = 2,
IPv6 = 3,
AddressFamilyMaxValue = 4,
}
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/** IPv4 prefix type. */
struct IPv4PrefixType {
1: required IPv4Address address;
2: required PrefixLenType prefixlen;
} (python.immutable = "")
/** IPv6 prefix type. */
struct IPv6PrefixType {
1: required IPv6Address address;
2: required PrefixLenType prefixlen;
} (python.immutable = "")
/** IP address type. */
union IPAddressType {
/** Content is IPv4 */
1: optional IPv4Address ipv4address;
/** Content is IPv6 */
2: optional IPv6Address ipv6address;
} (python.immutable = "")
/** Prefix advertisement.
@note: for interface
addresses the protocol can propagate the address part beyond
the subnet mask and on reachability computation that has to
be normalized. The non-significant bits can be used
for operational purposes.
*/
union IPPrefixType {
1: optional IPv4PrefixType ipv4prefix;
2: optional IPv6PrefixType ipv6prefix;
} (python.immutable = "")
/** Sequence of a prefix in case of move.
*/
struct PrefixSequenceType {
1: required IEEE802_1ASTimeStampType timestamp;
/** Transaction ID set by client in e.g. in 6LoWPAN. */
2: optional PrefixTransactionIDType transactionid;
}
/** Type of TIE.
*/
enum TIETypeType {
Illegal = 0,
TIETypeMinValue = 1,
/** first legal value */
NodeTIEType = 2,
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PrefixTIEType = 3,
PositiveDisaggregationPrefixTIEType = 4,
NegativeDisaggregationPrefixTIEType = 5,
PGPrefixTIEType = 6,
KeyValueTIEType = 7,
ExternalPrefixTIEType = 8,
PositiveExternalDisaggregationPrefixTIEType = 9,
TIETypeMaxValue = 10,
}
/** RIFT route types.
@note: The only purpose of those values is to introduce an
ordering whereas an implementation can choose internally
any other values as long the ordering is preserved
*/
enum RouteType {
Illegal = 0,
RouteTypeMinValue = 1,
/** First legal value. */
/** Discard routes are most preferred */
Discard = 2,
/** Local prefixes are directly attached prefixes on the
* system such as e.g. interface routes.
*/
LocalPrefix = 3,
/** Advertised in S-TIEs */
SouthPGPPrefix = 4,
/** Advertised in N-TIEs */
NorthPGPPrefix = 5,
/** Advertised in N-TIEs */
NorthPrefix = 6,
/** Externally imported north */
NorthExternalPrefix = 7,
/** Advertised in S-TIEs, either normal prefix or positive
disaggregation */
SouthPrefix = 8,
/** Externally imported south */
SouthExternalPrefix = 9,
/** Negative, transitive prefixes are least preferred */
NegativeSouthPrefix = 10,
RouteTypeMaxValue = 11,
}
B.3. encoding.thrift
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/**
Thrift file for packet encodings for RIFT
*/
include "common.thrift"
namespace py encoding
/** Represents protocol encoding schema major version */
const common.VersionType protocol_major_version = 5
/** Represents protocol encoding schema minor version */
const common.MinorVersionType protocol_minor_version = 0
/** Common RIFT packet header. */
struct PacketHeader {
/** Major version of protocol. */
1: required common.VersionType major_version =
protocol_major_version;
/** Minor version of protocol. */
2: required common.MinorVersionType minor_version =
protocol_minor_version;
/** Node sending the packet, in case of LIE/TIRE/TIDE
also the originator of it. */
3: required common.SystemIDType sender;
/** Level of the node sending the packet, required on everything
except LIEs. Lack of presence on LIEs indicates UNDEFINED_LEVEL
and is used in ZTP procedures.
*/
4: optional common.LevelType level;
}
/** Prefix community. */
struct Community {
/** Higher order bits */
1: required i32 top;
/** Lower order bits */
2: required i32 bottom;
} (python.immutable = "")
/** Neighbor structure. */
struct Neighbor {
/** System ID of the originator. */
1: required common.SystemIDType originator;
/** ID of remote side of the link. */
2: required common.LinkIDType remote_id;
} (python.immutable = "")
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/** Capabilities the node supports. */
struct NodeCapabilities {
/** Must advertise supported minor version dialect that way. */
1: required common.MinorVersionType protocol_minor_version =
protocol_minor_version;
/** indicates that node supports flood reduction. */
2: optional bool flood_reduction =
common.flood_reduction_default;
/** indicates place in hierarchy, i.e. top-of-fabric or
leaf only (in ZTP) or support for leaf-2-leaf
procedures. */
3: optional common.HierarchyIndications hierarchy_indications;
} (python.immutable = "")
/** Link capabilities. */
struct LinkCapabilities {
/** Indicates that the link is supporting BFD. */
1: optional bool bfd =
common.bfd_default;
/** Indicates whether the interface will support IPv4 forwarding. */
2: optional bool ipv4_forwarding_capable =
true;
} (python.immutable = "")
/** RIFT LIE Packet.
@note: this node's level is already included on the packet header
*/
struct LIEPacket {
/** Node or adjacency name. */
1: optional string name;
/** Local link ID. */
2: required common.LinkIDType local_id;
/** UDP port to which we can receive flooded TIEs. */
3: required common.UDPPortType flood_port =
common.default_tie_udp_flood_port;
/** Layer 3 MTU, used to discover mismatch. */
4: optional common.MTUSizeType link_mtu_size =
common.default_mtu_size;
/** Local link bandwidth on the interface. */
5: optional common.BandwithInMegaBitsType
link_bandwidth = common.default_bandwidth;
/** Reflects the neighbor once received to provide
3-way connectivity. */
6: optional Neighbor neighbor;
/** Node's PoD. */
7: optional common.PodType pod =
common.default_pod;
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/** Node capabilities supported. */
10: required NodeCapabilities node_capabilities;
/** Capabilities of this link. */
11: optional LinkCapabilities link_capabilities;
/** Required holdtime of the adjacency, i.e. for how
long a period should adjacency be kept up without valid LIE reception. */
12: required common.TimeIntervalInSecType
holdtime = common.default_lie_holdtime;
/** Optional, unsolicited, downstream assigned locally significant label
value for the adjacency. */
13: optional common.LabelType label;
/** Indicates that the level on the LIE must not be used
to derive a ZTP level by the receiving node. */
21: optional bool not_a_ztp_offer =
common.default_not_a_ztp_offer;
/** Indicates to northbound neighbor that it should
be reflooding TIEs received from this node to achieve flood
reduction and balancing for northbound flooding. */
22: optional bool you_are_flood_repeater =
common.default_you_are_flood_repeater;
/** Indicates to neighbor to flood node TIEs only and slow down
all other TIEs. Ignored when received from southbound neighbor. */
23: optional bool you_are_sending_too_quickly =
false;
/** Instance name in case multiple RIFT instances running on same
interface. */
24: optional string instance_name;
}
/** LinkID pair describes one of parallel links between two nodes. */
struct LinkIDPair {
/** Node-wide unique value for the local link. */
1: required common.LinkIDType local_id;
/** Received remote link ID for this link. */
2: required common.LinkIDType remote_id;
/** Describes the local interface index of the link. */
10: optional common.PlatformInterfaceIndex platform_interface_index;
/** Describes the local interface name. */
11: optional string platform_interface_name;
/** Indicates whether the link is secured, i.e. protected by
outer key, absence of this element means no indication,
undefined outer key means not secured. */
12: optional common.OuterSecurityKeyID
trusted_outer_security_key;
/** Indicates whether the link is protected by established
BFD session. */
13: optional bool bfd_up;
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/** Optional indication which address families are up on the
interface */
14: optional set<common.AddressFamilyType>
(python.immutable = "") address_families;
} (python.immutable = "")
/** Unique ID of a TIE. */
struct TIEID {
/** direction of TIE */
1: required common.TieDirectionType direction;
/** indicates originator of the TIE */
2: required common.SystemIDType originator;
/** type of the tie */
3: required common.TIETypeType tietype;
/** number of the tie */
4: required common.TIENrType tie_nr;
} (python.immutable = "")
/** Header of a TIE. */
struct TIEHeader {
/** ID of the tie. */
2: required TIEID tieid;
/** Sequence number of the tie. */
3: required common.SeqNrType seq_nr;
/** Absolute timestamp when the TIE was generated. */
10: optional common.IEEE802_1ASTimeStampType origination_time;
/** Original lifetime when the TIE was generated. */
12: optional common.LifeTimeInSecType origination_lifetime;
}
/** Header of a TIE as described in TIRE/TIDE.
*/
struct TIEHeaderWithLifeTime {
1: required TIEHeader header;
/** Remaining lifetime. */
2: required common.LifeTimeInSecType remaining_lifetime;
}
/** TIDE with *sorted* TIE headers. */
struct TIDEPacket {
/** First TIE header in the tide packet. */
1: required TIEID start_range;
/** Last TIE header in the tide packet. */
2: required TIEID end_range;
/** _Sorted_ list of headers. */
3: required list<TIEHeaderWithLifeTime>
(python.immutable = "") headers;
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}
/** TIRE packet */
struct TIREPacket {
1: required set<TIEHeaderWithLifeTime>
(python.immutable = "") headers;
}
/** neighbor of a node */
struct NodeNeighborsTIEElement {
/** level of neighbor */
1: required common.LevelType level;
/** Cost to neighbor. Ignore anything larger than `infinite_distance` and `invalid_distance` */
3: optional common.MetricType cost
= common.default_distance;
/** can carry description of multiple parallel links in a TIE */
4: optional set<LinkIDPair>
(python.immutable = "") link_ids;
/** total bandwith to neighbor as sum of all parallel links */
5: optional common.BandwithInMegaBitsType
bandwidth = common.default_bandwidth;
} (python.immutable = "")
/** Indication flags of the node. */
struct NodeFlags {
/** Indicates that node is in overload, do not transit traffic
through it. */
1: optional bool overload = common.overload_default;
} (python.immutable = "")
/** Description of a node. */
struct NodeTIEElement {
/** Level of the node. */
1: required common.LevelType level;
/** Node's neighbors. Multiple node TIEs can carry disjoint sets of neighbors. */
2: required map<common.SystemIDType,
NodeNeighborsTIEElement> neighbors;
/** Capabilities of the node. */
3: required NodeCapabilities capabilities;
/** Flags of the node. */
4: optional NodeFlags flags;
/** Optional node name for easier operations. */
5: optional string name;
/** PoD to which the node belongs. */
6: optional common.PodType pod;
/** optional startup time of the node */
7: optional common.TimestampInSecsType startup_time;
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/** If any local links are miscabled, this indication is flooded. */
10: optional set<common.LinkIDType>
(python.immutable = "") miscabled_links;
} (python.immutable = "")
/** Attributes of a prefix. */
struct PrefixAttributes {
/** Distance of the prefix. */
2: required common.MetricType metric
= common.default_distance;
/** Generic unordered set of route tags, can be redistributed
to other protocols or use within the context of real time
analytics. */
3: optional set<common.RouteTagType>
(python.immutable = "") tags;
/** Monotonic clock for mobile addresses. */
4: optional common.PrefixSequenceType monotonic_clock;
/** Indicates if the prefix is a node loopback. */
6: optional bool loopback = false;
/** Indicates that the prefix is directly attached. */
7: optional bool directly_attached = true;
/** link to which the address belongs to. */
10: optional common.LinkIDType from_link;
} (python.immutable = "")
/** TIE carrying prefixes */
struct PrefixTIEElement {
/** Prefixes with the associated attributes. */
1: required map<common.IPPrefixType, PrefixAttributes> prefixes;
} (python.immutable = "")
/** Generic key value pairs. */
struct KeyValueTIEElement {
1: required map<common.KeyIDType, binary> keyvalues;
} (python.immutable = "")
/** Single element in a TIE. */
union TIEElement {
/** Used in case of enum common.TIETypeType.NodeTIEType. */
1: optional NodeTIEElement node;
/** Used in case of enum common.TIETypeType.PrefixTIEType. */
2: optional PrefixTIEElement prefixes;
/** Positive prefixes (always southbound). */
3: optional PrefixTIEElement positive_disaggregation_prefixes;
/** Transitive, negative prefixes (always southbound) */
5: optional PrefixTIEElement negative_disaggregation_prefixes;
/** Externally reimported prefixes. */
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6: optional PrefixTIEElement external_prefixes;
/** Positive external disaggregated prefixes (always southbound). */
7: optional PrefixTIEElement
positive_external_disaggregation_prefixes;
/** Key-Value store elements. */
9: optional KeyValueTIEElement keyvalues;
} (python.immutable = "")
/** TIE packet */
struct TIEPacket {
1: required TIEHeader header;
2: required TIEElement element;
}
/** Content of a RIFT packet. */
union PacketContent {
1: optional LIEPacket lie;
2: optional TIDEPacket tide;
3: optional TIREPacket tire;
4: optional TIEPacket tie;
}
/** RIFT packet structure. */
struct ProtocolPacket {
1: required PacketHeader header;
2: required PacketContent content;
}
Appendix C. Constants
C.1. Configurable Protocol Constants
This section gathers constants that are provided in the schema files
and in the document.
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+================+==============+==================================+
| | Type | Value |
+================+==============+==================================+
| LIE IPv4 | Default | 224.0.0.120 or all-rift-routers |
| Multicast | Value, | to be assigned in IPv4 Multicast |
| Address | Configurable | Address Space Registry in Local |
| | | Network Control Block |
+----------------+--------------+----------------------------------+
| LIE IPv6 | Default | FF02::A1F7 or all-rift-routers |
| Multicast | Value, | to be assigned in IPv6 Multicast |
| Address | Configurable | Address Assignments |
+----------------+--------------+----------------------------------+
| LIE | Default | 914 |
| Destination | Value, | |
| Port | Configurable | |
+----------------+--------------+----------------------------------+
| Level value | Constant | 24 |
| for | | |
| TOP_OF_FABRIC | | |
| flag | | |
+----------------+--------------+----------------------------------+
| Default LIE | Default | 3 seconds |
| Holdtime | Value, | |
| | Configurable | |
+----------------+--------------+----------------------------------+
| TIE | Default | 1 second |
| Retransmission | Value | |
| Interval | | |
+----------------+--------------+----------------------------------+
| TIDE | Default | 5 seconds |
| Generation | Value, | |
| Interval | Configurable | |
+----------------+--------------+----------------------------------+
| MIN_TIEID | Constant | TIE Key with minimal values: |
| signifies | | TIEID(originator=0, |
| start of TIDEs | | tietype=TIETypeMinValue, |
| | | tie_nr=0, direction=South) |
+----------------+--------------+----------------------------------+
| MAX_TIEID | Constant | TIE Key with maximal values: |
| signifies end | | TIEID(originator=MAX_UINT64, |
| of TIDEs | | tietype=TIETypeMaxValue, |
| | | tie_nr=MAX_UINT64, |
| | | direction=North) |
+----------------+--------------+----------------------------------+
Table 41: all_constants
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Authors' Addresses
Tony Przygienda (editor)
Juniper
1137 Innovation Way
Sunnyvale, CA
United States of America
Email: prz@juniper.net
Alankar Sharma
Comcast
1800 Bishops Gate Blvd
Mount Laurel, NJ 08054
United States of America
Email: Alankar_Sharma@comcast.com
Pascal Thubert
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
06254 MOUGINS - Sophia Antipolis
France
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
Bruno Rijsman
Individual
Email: brunorijsman@gmail.com
Dmitry Afanasiev
Yandex
Email: fl0w@yandex-team.ru
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