RIFT Working Group A. Przygienda, Ed.
Internet-Draft Juniper
Intended status: Standards Track A. Sharma
Expires: March 11, 2020 Comcast
P. Thubert
Cisco
Bruno. Rijsman
Individual
Dmitry. Afanasiev
Yandex
September 8, 2019
RIFT: Routing in Fat Trees
draft-ietf-rift-rift-08
Abstract
This document outlines a specialized, dynamic routing protocol for
Clos and fat-tree network topologies. The protocol (1) deals with
fully automated construction of fat-tree topologies based on
detection of links, (2) minimizes the amount of routing state held at
each level, (3) automatically prunes and load balances topology
flooding exchanges over a sufficient subset of links, (4) supports
automatic disaggregation of prefixes on link and node failures to
prevent black-holing and suboptimal routing, (5) allows traffic
steering and re-routing policies, (6) allows loop-free non-ECMP
forwarding, (7) automatically re-balances traffic towards the spines
based on bandwidth available and finally (8) provides mechanisms to
synchronize a limited key-value data-store that can be used after
protocol convergence to e.g. bootstrap higher levels of
functionality on nodes.
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Table of Contents
1. Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 8
3. Reference Frame . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 8
3.2. Topology . . . . . . . . . . . . . . . . . . . . . . . . 12
4. Requirement Considerations . . . . . . . . . . . . . . . . . 14
5. RIFT: Routing in Fat Trees . . . . . . . . . . . . . . . . . 17
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 18
5.1.1. Properties . . . . . . . . . . . . . . . . . . . . . 18
5.1.2. Generalized Topology View . . . . . . . . . . . . . . 18
5.1.3. Fallen Leaf Problem . . . . . . . . . . . . . . . . . 28
5.1.4. Discovering Fallen Leaves . . . . . . . . . . . . . . 30
5.1.5. Addressing the Fallen Leaves Problem . . . . . . . . 31
5.2. Specification . . . . . . . . . . . . . . . . . . . . . . 32
5.2.1. Transport . . . . . . . . . . . . . . . . . . . . . . 32
5.2.2. Link (Neighbor) Discovery (LIE Exchange) . . . . . . 33
5.2.3. Topology Exchange (TIE Exchange) . . . . . . . . . . 35
5.2.3.1. Topology Information Elements . . . . . . . . . . 35
5.2.3.2. South- and Northbound Representation . . . . . . 36
5.2.3.3. Flooding . . . . . . . . . . . . . . . . . . . . 38
5.2.3.4. TIE Flooding Scopes . . . . . . . . . . . . . . . 39
5.2.3.5. 'Flood Only Node TIEs' Bit . . . . . . . . . . . 41
5.2.3.6. Initial and Periodic Database Synchronization . . 42
5.2.3.7. Purging and Roll-Overs . . . . . . . . . . . . . 42
5.2.3.8. Southbound Default Route Origination . . . . . . 43
5.2.3.9. Northbound TIE Flooding Reduction . . . . . . . . 43
5.2.3.10. Special Considerations . . . . . . . . . . . . . 48
5.2.4. Reachability Computation . . . . . . . . . . . . . . 49
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5.2.4.1. Northbound SPF . . . . . . . . . . . . . . . . . 49
5.2.4.2. Southbound SPF . . . . . . . . . . . . . . . . . 50
5.2.4.3. East-West Forwarding Within a non-ToF Level . . . 50
5.2.4.4. East-West Links Within ToF Level . . . . . . . . 50
5.2.5. Automatic Disaggregation on Link & Node Failures . . 51
5.2.5.1. Positive, Non-transitive Disaggregation . . . . . 51
5.2.5.2. Negative, Transitive Disaggregation for Fallen
Leafs . . . . . . . . . . . . . . . . . . . . . . 54
5.2.6. Attaching Prefixes . . . . . . . . . . . . . . . . . 56
5.2.7. Optional Zero Touch Provisioning (ZTP) . . . . . . . 65
5.2.7.1. Terminology . . . . . . . . . . . . . . . . . . . 66
5.2.7.2. Automatic SystemID Selection . . . . . . . . . . 67
5.2.7.3. Generic Fabric Example . . . . . . . . . . . . . 68
5.2.7.4. Level Determination Procedure . . . . . . . . . . 69
5.2.7.5. Resulting Topologies . . . . . . . . . . . . . . 70
5.2.8. Stability Considerations . . . . . . . . . . . . . . 72
5.3. Further Mechanisms . . . . . . . . . . . . . . . . . . . 72
5.3.1. Overload Bit . . . . . . . . . . . . . . . . . . . . 72
5.3.2. Optimized Route Computation on Leafs . . . . . . . . 72
5.3.3. Mobility . . . . . . . . . . . . . . . . . . . . . . 73
5.3.3.1. Clock Comparison . . . . . . . . . . . . . . . . 74
5.3.3.2. Interaction between Time Stamps and Sequence
Counters . . . . . . . . . . . . . . . . . . . . 74
5.3.3.3. Anycast vs. Unicast . . . . . . . . . . . . . . . 75
5.3.3.4. Overlays and Signaling . . . . . . . . . . . . . 75
5.3.4. Key/Value Store . . . . . . . . . . . . . . . . . . . 76
5.3.4.1. Southbound . . . . . . . . . . . . . . . . . . . 76
5.3.4.2. Northbound . . . . . . . . . . . . . . . . . . . 76
5.3.5. Interactions with BFD . . . . . . . . . . . . . . . . 76
5.3.6. Fabric Bandwidth Balancing . . . . . . . . . . . . . 77
5.3.6.1. Northbound Direction . . . . . . . . . . . . . . 77
5.3.6.2. Southbound Direction . . . . . . . . . . . . . . 79
5.3.7. Label Binding . . . . . . . . . . . . . . . . . . . . 80
5.3.8. Segment Routing Support with RIFT . . . . . . . . . . 80
5.3.8.1. Global Segment Identifiers Assignment . . . . . . 80
5.3.8.2. Distribution of Topology Information . . . . . . 80
5.3.9. Leaf to Leaf Procedures . . . . . . . . . . . . . . . 81
5.3.10. Address Family and Multi Topology Considerations . . 81
5.3.11. Reachability of Internal Nodes in the Fabric . . . . 81
5.3.12. One-Hop Healing of Levels with East-West Links . . . 82
5.4. Security . . . . . . . . . . . . . . . . . . . . . . . . 82
5.4.1. Security Model . . . . . . . . . . . . . . . . . . . 82
5.4.2. Security Mechanisms . . . . . . . . . . . . . . . . . 84
5.4.3. Security Envelope . . . . . . . . . . . . . . . . . . 84
5.4.4. Weak Nonces . . . . . . . . . . . . . . . . . . . . . 87
5.4.5. Lifetime . . . . . . . . . . . . . . . . . . . . . . 88
5.4.6. Key Management . . . . . . . . . . . . . . . . . . . 88
5.4.7. Security Association Changes . . . . . . . . . . . . 88
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6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 89
6.1. Normal Operation . . . . . . . . . . . . . . . . . . . . 89
6.2. Leaf Link Failure . . . . . . . . . . . . . . . . . . . . 90
6.3. Partitioned Fabric . . . . . . . . . . . . . . . . . . . 91
6.4. Northbound Partitioned Router and Optional East-West
Links . . . . . . . . . . . . . . . . . . . . . . . . . . 93
7. Implementation and Operation: Further Details . . . . . . . . 93
7.1. Considerations for Leaf-Only Implementation . . . . . . . 93
7.2. Considerations for Spine Implementation . . . . . . . . . 94
7.3. Adaptations to Other Proposed Data Center Topologies . . 94
7.4. Originating Non-Default Route Southbound . . . . . . . . 95
8. Security Considerations . . . . . . . . . . . . . . . . . . . 95
8.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 95
8.2. ZTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
8.3. Lifetime . . . . . . . . . . . . . . . . . . . . . . . . 96
8.4. Packet Number . . . . . . . . . . . . . . . . . . . . . . 96
8.5. Outer Fingerprint Attacks . . . . . . . . . . . . . . . . 96
8.6. TIE Origin Fingerprint DoS Attacks . . . . . . . . . . . 96
8.7. Host Implementations . . . . . . . . . . . . . . . . . . 97
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 97
9.1. Requested Multicast and Port Numbers . . . . . . . . . . 97
9.2. Requested Registries with Suggested Values . . . . . . . 97
9.2.1. RIFT/common/AddressFamilyType . . . . . . . . . . . . 98
9.2.1.1. Requested Entries . . . . . . . . . . . . . . . . 98
9.2.2. RIFT/common/HierarchyIndications . . . . . . . . . . 98
9.2.2.1. Requested Entries . . . . . . . . . . . . . . . . 98
9.2.3. RIFT/common/IEEE802_1ASTimeStampType . . . . . . . . 98
9.2.3.1. Requested Entries . . . . . . . . . . . . . . . . 98
9.2.4. RIFT/common/IPAddressType . . . . . . . . . . . . . . 98
9.2.4.1. Requested Entries . . . . . . . . . . . . . . . . 98
9.2.5. RIFT/common/IPPrefixType . . . . . . . . . . . . . . 99
9.2.5.1. Requested Entries . . . . . . . . . . . . . . . . 99
9.2.6. RIFT/common/IPv4PrefixType . . . . . . . . . . . . . 99
9.2.6.1. Requested Entries . . . . . . . . . . . . . . . . 99
9.2.7. RIFT/common/IPv6PrefixType . . . . . . . . . . . . . 99
9.2.7.1. Requested Entries . . . . . . . . . . . . . . . . 99
9.2.8. RIFT/common/PrefixSequenceType . . . . . . . . . . . 99
9.2.8.1. Requested Entries . . . . . . . . . . . . . . . . 99
9.2.9. RIFT/common/RouteType . . . . . . . . . . . . . . . . 100
9.2.9.1. Requested Entries . . . . . . . . . . . . . . . . 100
9.2.10. RIFT/common/TIETypeType . . . . . . . . . . . . . . . 100
9.2.10.1. Requested Entries . . . . . . . . . . . . . . . 100
9.2.11. RIFT/common/TieDirectionType . . . . . . . . . . . . 101
9.2.11.1. Requested Entries . . . . . . . . . . . . . . . 101
9.2.12. RIFT/encoding/Community . . . . . . . . . . . . . . . 101
9.2.12.1. Requested Entries . . . . . . . . . . . . . . . 101
9.2.13. RIFT/encoding/KeyValueTIEElement . . . . . . . . . . 101
9.2.13.1. Requested Entries . . . . . . . . . . . . . . . 101
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9.2.14. RIFT/encoding/LIEPacket . . . . . . . . . . . . . . . 102
9.2.14.1. Requested Entries . . . . . . . . . . . . . . . 102
9.2.15. RIFT/encoding/LinkCapabilities . . . . . . . . . . . 103
9.2.15.1. Requested Entries . . . . . . . . . . . . . . . 103
9.2.16. RIFT/encoding/LinkIDPair . . . . . . . . . . . . . . 103
9.2.16.1. Requested Entries . . . . . . . . . . . . . . . 103
9.2.17. RIFT/encoding/Neighbor . . . . . . . . . . . . . . . 104
9.2.17.1. Requested Entries . . . . . . . . . . . . . . . 104
9.2.18. RIFT/encoding/NodeCapabilities . . . . . . . . . . . 104
9.2.18.1. Requested Entries . . . . . . . . . . . . . . . 104
9.2.19. RIFT/encoding/NodeFlags . . . . . . . . . . . . . . . 105
9.2.19.1. Requested Entries . . . . . . . . . . . . . . . 105
9.2.20. RIFT/encoding/NodeNeighborsTIEElement . . . . . . . . 105
9.2.20.1. Requested Entries . . . . . . . . . . . . . . . 105
9.2.21. RIFT/encoding/NodeTIEElement . . . . . . . . . . . . 105
9.2.21.1. Requested Entries . . . . . . . . . . . . . . . 106
9.2.22. RIFT/encoding/PacketContent . . . . . . . . . . . . . 106
9.2.22.1. Requested Entries . . . . . . . . . . . . . . . 106
9.2.23. RIFT/encoding/PacketHeader . . . . . . . . . . . . . 106
9.2.23.1. Requested Entries . . . . . . . . . . . . . . . 106
9.2.24. RIFT/encoding/PrefixAttributes . . . . . . . . . . . 107
9.2.24.1. Requested Entries . . . . . . . . . . . . . . . 107
9.2.25. RIFT/encoding/PrefixTIEElement . . . . . . . . . . . 107
9.2.25.1. Requested Entries . . . . . . . . . . . . . . . 107
9.2.26. RIFT/encoding/ProtocolPacket . . . . . . . . . . . . 108
9.2.26.1. Requested Entries . . . . . . . . . . . . . . . 108
9.2.27. RIFT/encoding/TIDEPacket . . . . . . . . . . . . . . 108
9.2.27.1. Requested Entries . . . . . . . . . . . . . . . 108
9.2.28. RIFT/encoding/TIEElement . . . . . . . . . . . . . . 108
9.2.28.1. Requested Entries . . . . . . . . . . . . . . . 108
9.2.29. RIFT/encoding/TIEHeader . . . . . . . . . . . . . . . 109
9.2.29.1. Requested Entries . . . . . . . . . . . . . . . 110
9.2.30. RIFT/encoding/TIEHeaderWithLifeTime . . . . . . . . . 110
9.2.30.1. Requested Entries . . . . . . . . . . . . . . . 110
9.2.31. RIFT/encoding/TIEID . . . . . . . . . . . . . . . . . 110
9.2.31.1. Requested Entries . . . . . . . . . . . . . . . 111
9.2.32. RIFT/encoding/TIEPacket . . . . . . . . . . . . . . . 111
9.2.32.1. Requested Entries . . . . . . . . . . . . . . . 111
9.2.33. RIFT/encoding/TIREPacket . . . . . . . . . . . . . . 111
9.2.33.1. Requested Entries . . . . . . . . . . . . . . . 111
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 111
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 112
11.1. Normative References . . . . . . . . . . . . . . . . . . 112
11.2. Informative References . . . . . . . . . . . . . . . . . 114
Appendix A. Sequence Number Binary Arithmetic . . . . . . . . . 116
Appendix B. Information Elements Schema . . . . . . . . . . . . 117
B.1. common.thrift . . . . . . . . . . . . . . . . . . . . . . 118
B.2. encoding.thrift . . . . . . . . . . . . . . . . . . . . . 124
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Appendix C. Finite State Machines and Precise Operational
Specifications . . . . . . . . . . . . . . . . . . . 132
C.1. LIE FSM . . . . . . . . . . . . . . . . . . . . . . . . . 133
C.2. ZTP FSM . . . . . . . . . . . . . . . . . . . . . . . . . 139
C.3. Flooding Procedures . . . . . . . . . . . . . . . . . . . 147
C.3.1. FloodState Structure per Adjacency . . . . . . . . . 147
C.3.2. TIDEs . . . . . . . . . . . . . . . . . . . . . . . . 149
C.3.2.1. TIDE Generation . . . . . . . . . . . . . . . . . 149
C.3.2.2. TIDE Processing . . . . . . . . . . . . . . . . . 150
C.3.3. TIREs . . . . . . . . . . . . . . . . . . . . . . . . 151
C.3.3.1. TIRE Generation . . . . . . . . . . . . . . . . . 151
C.3.3.2. TIRE Processing . . . . . . . . . . . . . . . . . 151
C.3.4. TIEs Processing on Flood State Adjacency . . . . . . 152
C.3.5. TIEs Processing When LSDB Received Newer Version on
Other Adjacencies . . . . . . . . . . . . . . . . . . 153
C.3.6. Sending TIEs . . . . . . . . . . . . . . . . . . . . 153
Appendix D. Constants . . . . . . . . . . . . . . . . . . . . . 153
D.1. Configurable Protocol Constants . . . . . . . . . . . . . 153
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 155
1. Authors
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 Networks | Comcast | Cisco
Bruno Rijsman | Ilya Vershkov | Dmitry Afanasiev
Individual | Mellanox | Yandex
Don Fedyk | Alia Atlas | John Drake
Individual | Individual | Juniper
Table 1: RIFT Authors
2. Introduction
Clos [CLOS] and Fat-Tree [FATTREE] topologies 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. Today's current routing protocols were geared towards a
network with an irregular topology and low degree of connectivity
originally but given they were the only available options,
consequently several attempts to apply those protocols to Clos have
been made. Most successfully BGP [RFC4271] [RFC7938] has been
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extended to this purpose, not as much due to its inherent suitability
but rather because the perceived capability to easily modify BGP and
the immanent difficulties with link-state [DIJKSTRA] based protocols
to optimize topology exchange and converge quickly in large scale
densely meshed topologies. The incumbent protocols precondition
normally extensive configuration or provisioning during bring up and
re-dimensioning which is only viable for a set of organizations with
according networking operation skills and budgets. For the majority
of data center consumers a preferable protocol would be one that
auto-configures itself and deals with failures and misconfigurations
with a minimum of human intervention only. 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, much like compute or storage is consumed today.
In looking at the problem through the lens of data center
requirements, an optimal approach does not seem however to be a
simple modification of either a link-state (distributed computation)
or distance-vector (diffused computation) approach but rather a
mixture of both, colloquially best described as "link-state towards
the spine" and "distance vector towards the leafs". 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 be addressed. The
approach RIFT takes is described in Section 5.2.5 and is basically
based on automatic, sufficient disaggregation of prefixes.
For the visually oriented reader, Figure 1 presents a first level
simplified view of the resulting information and routes on a RIFT
fabric. The top of the fabric is holding in its link-state database
the nodes below it and the routes to them. In the second row of the
database table we indicate that partial information of other nodes in
the same level is available as well. The details of how this is
achieved will be postponed for the moment. When we look at the
"bottom" of the fabric, the leafs, we see that the topology is
basically empty and they only hold a load balanced default route to
the next level.
The balance of this document details the requirements of a dedicated
fabric routing protocol, fills in the specification details and
ultimately includes resulting security considerations.
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. [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
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. Reference Frame
3.1. Terminology
This section presents the terminology used in this document. It is
assumed that the reader is thoroughly familiar with the terms and
concepts used in OSPF [RFC2328] and IS-IS [ISO10589-Second-Edition],
[ISO10589] as well as the according graph theoretical concepts of
shortest path first (SPF) [DIJKSTRA] computation and directed acyclic
graphs (DAG).
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 PoDs and one or multiple ToF
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planes. Several modifications such as leaf-2-leaf shortcuts and
multiple level shortcuts are possible and described further in the
document.
Folded Spine-and-Leaf: In case Clos fabric input and output stages
are analogous, the fabric can be "folded" to build a "superspine"
or top which we will call 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 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. As footnote: Clos terminology
uses often the concept of "stage" but due to the folded nature of
the Fat Tree we do not use it to prevent misunderstandings.
Superspine/Aggregation or Spine/Edge Levels: Traditional names in
5-stages folded Clos for Level 2, 1 and 0 respectively. Level 0
is often called leaf as well. We normalize this language to talk
about leafs, spines and top-of-fabric (ToF).
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. We number PoDs to distinguish them
and use PoD #0 to denote "undefined" 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 "undefined" PoD value to indicate the equivalent of
"any" PoD.
Spine: Any nodes north of leafs and south of top-of-fabric nodes.
Multiple layers of spines in a PoD are possible.
Leaf: A node without southbound adjacencies. Its level is 0 (except
cases where it is deriving its level via ZTP and is running
without LEAF_ONLY which will be explained in Section 5.2.7).
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
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independent planes. Introduction and Section 5.1.2 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 basically 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, we will be using in different
situations the directionality of the compass. I.e., 'south' or
'southbound' mean moving towards the bottom of the Clos or Fat
Tree network and '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 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/leafs are multi-homed and consecutively participate
in routing.
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" back up north to
allow nodes in same level without E-W links to "see" each other.
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, in a fashion similar to ISIS
LSPs or OSPF LSAs. We will talk about N-TIEs when talking about
TIEs in the northbound representation and S-TIEs for the
southbound equivalent.
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Node TIE: This stands as acronym for a "Node Topology Information
Element" that contains all adjacencies the node discovered and
information about node itself.
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 N-TIE and in case of S-TIE the necessary default
the node passes southbound.
Key Value TIE: A S-TIE that is carrying a set of key value pairs
[DYNAMO]. It can be used to distribute information in the
southbound direction within the protocol.
TIDE: Topology Information Description Element, equivalent to CSNP
in ISIS.
TIRE: Topology Information Request Element, equivalent to PSNP in
ISIS. It can both confirm received and request missing TIEs.
De-aggregation/Disaggregation: Process in which a node decides to
advertise certain prefixes it received in N-TIEs to prevent black-
holing and suboptimal routing upon link failures.
LIE: This is an acronym for a "Link Information Element", largely
equivalent to HELLOs in IGPs and exchanged over all the links
between systems running RIFT to form adjacencies.
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. They are
similar to MPR in OSLR. The document sometimes calls them flood
leaders as well.
Bandwidth Adjusted Distance (BAD): This is an acronym for Bandwidth
Adjusted Distance. Each RIFT node calculates the amount of
northbound bandwidth available towards a node compared to other
nodes at the same level and modifies the default route distance
accordingly to allow for the lower level to adjust their load
balancing towards spines.
Overloaded: Applies to a node advertising `overload` attribute as
set. The semantics closely follow the meaning of the same
attribute in [ISO10589-Second-Edition].
Interface: A layer 3 entity over which RIFT control packets are
exchanged.
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Adjacency: RIFT tries to form a unique adjacency over an interface
and exchange local configuration and necessary ZTP information.
Neighbor: Once a three way adjacency has been formed a neighborship
relationship contains the neighbor's properties. Multiple
adjacencies can be formed to a neighbor via parallel interfaces
but such adjacencies are NOT sharing a neighbor structure. Saying
"neighbor" is thus equivalent to saying "a three way adjacency".
Cost: The term signifies the weighted distance between two
neighbors.
Distance: Sum of costs (bound by infinite distance) between two
nodes.
Metric: Without going deeper into the proper differentiation, a
metric is equivalent to distance.
3.2. Topology
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. +--------+ +--------+ ^ N
. |ToF 21| |ToF 22| |
.Level 2 ++-+--+-++ ++-+--+-++ <-*-> E/W
. | | | | | | | | |
. P111/2| |P121 | | | | S v
. ^ ^ ^ ^ | | | |
. | | | | | | | |
. +--------------+ | +-----------+ | | | +---------------+
. | | | | | | | |
. South +-----------------------------+ | | ^
. | | | | | | | All TIEs
. 0/0 0/0 0/0 +-----------------------------+ |
. v v v | | | | |
. | | +-+ +<-0/0----------+ | |
. | | | | | | | |
.+-+----++ optional +-+----++ ++----+-+ ++-----++
.| | E/W link | | | | | |
.|Spin111+----------+Spin112| |Spin121| |Spin122|
.+-+---+-+ ++----+-+ +-+---+-+ ++---+--+
. | | | South | | | |
. | +---0/0--->-----+ 0/0 | +----------------+ |
. 0/0 | | | | | | |
. | +---<-0/0-----+ | v | +--------------+ | |
. v | | | | | | |
.+-+---+-+ +--+--+-+ +-+---+-+ +---+-+-+
.| | (L2L) | | | | Level 0 | |
.|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
We will use topology in Figure 2 (called commonly a fat tree/network
in modern IP fabric considerations [VAHDAT08] as homonym to the
original definition of the term [FATTREE]) 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 5.1.2.
4. Requirement Considerations
[RFC7938] gives the original set of requirements augmented here based
upon recent experience in the operation of fat-tree networks.
REQ1: The control protocol should discover the physical links
automatically and be able to detect cabling that violates
fat-tree topology constraints. It must react accordingly to
such mis-cabling attempts, at a minimum preventing
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adjacencies between nodes from being formed and traffic from
being forwarded on those mis-cabled links. E.g. connecting
a leaf to a spine at level 2 should be detected and ideally
prevented.
REQ2: A node without any configuration beside default values
should come up at the correct level in any PoD it is
introduced into. Optionally, it must be possible to
configure nodes to restrict their participation to the
PoD(s) targeted at any level.
REQ3: Optionally, the protocol should allow to provision IP
fabrics where the individual switches carry no configuration
information and are all deriving their level from a "seed".
Observe that this requirement may collide with the desire to
detect cabling misconfiguration and with that only one of
the requirements can be fully met in a chosen configuration
mode.
REQ4: The solution should allow for minimum size routing
information base and forwarding tables at leaf level for
speed, cost and simplicity reasons. Holding excessive
amount of information away from leaf nodes simplifies
operation and lowers cost of the underlay and allows to
scale and introduce proper multi-homing down to the server
level. The routing solution should allow for easy
instantiation of multiple routing planes. Coupled with
mobility defined in Paragraph 17 this should allow for
"light-weight" overlays on an IP fabric with e.g. native
IPv6 mobility support.
REQ5: Very high degree of ECMP must be supported. Maximum ECMP is
currently understood as the most efficient routing approach
to maximize the throughput of switching fabrics
[MAKSIC2013].
REQ6: Non equal cost anycast must be supported to allow for easy
and robust multi-homing of services without regressing to
careful balancing of link costs.
REQ7: Traffic engineering should be allowed by modification of
prefixes and/or their next-hops.
REQ8: The solution should allow for access to link states of the
whole topology to enable efficient support for modern
control architectures like SPRING [RFC7855] or PCE
[RFC4655].
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REQ9: The solution should easily accommodate opaque data to be
carried throughout the topology to subsets of nodes. This
can be used for many purposes, one of them being a key-value
store that allows bootstrapping of nodes based right at the
time of topology discovery. Another use is distributing MAC
to L3 address binding from the leafs up north in case of
e.g. DHCP.
REQ10: Nodes should be taken out and introduced into production
with minimum wait-times and minimum of "shaking" of the
network, i.e. radius of propagation (often called "blast
radius") of changed information should be as small as
feasible.
REQ11: The protocol should allow for maximum aggregation of carried
routing information while at the same time automatically de-
aggregating the prefixes to prevent black-holing in case of
failures. The de-aggregation should support maximum
possible ECMP/N-ECMP remaining after failure.
REQ12: Reducing the scope of communication needed throughout the
network on link and state failure, as well as reducing
advertisements of repeating or idiomatic information in
stable state is highly desirable since it leads to better
stability and faster convergence behavior.
REQ13: Under normal, fully converged condition, once a packet is
forwarded along a link in a "southbound" direction, it must
not take any further "northbound" links (Valley Free
Routing). Taking a path through the spine in cases where a
shorter path is available is highly undesirable (Bow Tying).
REQ14: Parallel links between same set of nodes must be
distinguishable for SPF, failure and traffic engineering
purposes.
REQ15: The protocol must support interfaces sharing the same
address. Specifically, it must operate in presence of
unnumbered links (even parallel ones) and/or links of a
single node being configured with same addresses.
REQ16: It would be desirable to achieve fast re-balancing of flows
when links, especially towards the spines are lost or
provisioned without regressing to per flow traffic
engineering which introduces significant amount of
complexity while possibly not being reactive enough to
account for short-lived flows.
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REQ17: The control plane should be able to unambiguously determine
the current point of attachment (which port on which leaf
node) of a prefix, even in a context of fast mobility, e.g.,
when the prefix is a host address on a wireless node that 1)
may associate to any of multiple access points (APs) that
are attached to different ports on a same leaf node or to
different leaf nodes, and 2) may move and reassociate
several times to a different access point within a sub-
second period.
REQ18: The protocol must provide security mechanisms that allow the
operator to restrict nodes, especially leaf nodes without
proper credentials, from forming a three-way adjacency and
participating in routing.
Following list represents non-requirements:
PEND1: Supporting anything but point-to-point links is not
necessary.
Finally, following are the non-requirements:
NONREQ1: Broadcast media support is unnecessary. However,
miscabling leading to multiple nodes on a broadcast
segment must be operationally easily recognizable and
detectable while not taxing the protocol excessively.
NONREQ2: Purging link state elements is unnecessary given its
fragility and complexity and today's large memory size on
even modest switches and routers.
NONREQ3: Special support for layer 3 multi-hop adjacencies is not
part of the protocol specification. Such support can be
easily provided by using tunneling technologies the same
way IGPs today are solving the problem.
5. RIFT: Routing in Fat Trees
Derived from the above requirements we present a detailed outline of
a protocol optimized for Routing in Fat Trees (RIFT) that in most
abstract terms has many properties of a modified link-state protocol
[RFC2328][ISO10589-Second-Edition] when "pointing north" and distance
vector [RFC4271] protocol when "pointing south". While this is an
unusual combination, it does quite naturally exhibit the desirable
properties we seek.
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5.1. Overview
5.1.1. Properties
The most singular property of RIFT is that it floods flat link-state
information northbound only so that each level obtains the full
topology of levels south of it. That information is never flooded
East-West (we'll talk about exceptions later) or back South again.
In the southbound direction the protocol operates like a "fully
summarizing, unidirectional" path vector protocol or rather a
distance vector with implicit split horizon whereas the information
propagates one hop south and is 're-advertised' by nodes at next
lower level, normally just the default route. However, RIFT uses
flooding in the southern direction as well to avoid the necessity to
build an update per adjacency. We omit describing the East-West
direction out for the moment.
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 ultimately leads in hop-by-hop forwarding substrates to
utilization of variants of shortest paths only. RIFT under normal
conditions does not need to reconcile same reachability information
from multiple directions and its computation principles (south
forwarding direction is always prefered) leads to valley-free
forwarding behavior. And since valley free routing is loop-free it
can use all feasible paths, 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 accordingly partitioned into "north
representation" and "south representation" TIEs. In simplest terms
the N-TIEs contain a link state topology description of lower levels
and and S-TIEs carry simply default routes of the level above. This
oversimplified view will be refined gradually in following sections
while introducing protocol procedures aimed to fulfill the described
requirements.
5.1.2. Generalized Topology View
This section will shed some light on the topologies addresses by RIFT
including multi plane fabrics and their related implications.
Readers that are only interested in single plane designs, i.e. all
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top-of-fabric nodes being topologically equal and initially connected
to all the switches at the level below them can skip this section and
resulting Section 5.2.5.2 as well.
It is quite difficult to visualize multi plane design which are
effectively multi-dimensional switching matrices. To cope with that,
we will introduce a methodology allowing us to depict the
connectivity in a two-dimensional plane. Further, we will leverage
the fact that we are dealing basically with crossbar fabrics stacked
on top of each other where ports align "on top of each other" in a
regular fashion.
As 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 introduced Section 3.1 and it is
paramount to have it present to follow the rest of this section
correctly.
The typical topology for which RIFT is defined is built of a number P
of PoDs, connected together by a number S of ToF nodes. A PoD node
has a number of ports called Radix, with half of them (K=Radix/2)
used to connect host devices from the south, and half to connect to
interleaved PoD Top-Level switches to the north. Ratio K can be
chosen differently without loss of generality when port speeds differ
or fabric is oversubscribed but K=R/2 allows for more readable
representation whereby there are as many ports facing north as south
on any intermediate node. We represent a node hence 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 and for lack of a better
symbol, we have chosen to use the "HH" symbol as ASCII visualisation
of a RJ45 jack. In that example, K_LEAF is chosen to be 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
+----+
| |
| HH | e.g., Radix = 12, K_LEAF = 6
| |
| HH |
| | -------------------------
| HH ------- Physical Port (Ethernet) ----+
| | ------------------------- |
| HH | |
| | |
| HH | |
| | |
| HH | |
| | |
+----+ |
|| || || || || || ||
+----+ +------------------------------------------------+
| | | |
+----+ +------------------------------------------------+
|| || || || || || ||
Side views
Figure 4: A Leaf Node, K_LEAF=6
The Radix of a node on top of a PoD 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, we
could have switches with K_TOP southern ports on nodes at the top of
the PoD that is not necessarily the same as K_LEAF; for instance, in
the representations below, we pick a K_LEAF of 6 and a K_TOP of 8.
In order to form a crossbar, we need K_TOP Leaf Nodes as illustrated
in Figure 5.
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+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
| | | | | | | | | | | | | | | |
| HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH |
| | | | | | | | | | | | | | | |
| HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH |
| | | | | | | | | | | | | | | |
| HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH |
| | | | | | | | | | | | | | | |
| HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH |
| | | | | | | | | | | | | | | |
| HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH |
| | | | | | | | | | | | | | | |
| HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH |
| | | | | | | | | | | | | | | |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
Figure 5: Southern View of a PoD, K_TOP=8
The K_TOP Leaf Nodes are fully interconnected with the K_LEAF PoD-top
nodes, providing a connectivity that can be represented as a crossbar
as seen from the north and illustrated in Figure 6. The result is
that, in the absence of a breakage, a packet entering the PoD from
North on any port can be routed to any port on the south of the PoD
and vice versa.
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E<-*->W
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
| | | | | | | | | | | | | | | |
+----------------------------------------------------------------+
| HH HH HH HH HH HH HH HH |
+----------------------------------------------------------------+
+----------------------------------------------------------------+
| HH HH HH HH HH HH HH HH |
+----------------------------------------------------------------+
+----------------------------------------------------------------+
| HH HH HH HH HH HH HH HH |
+----------------------------------------------------------------+
+----------------------------------------------------------------+
| HH HH HH HH HH HH HH HH |
+----------------------------------------------------------------+
+----------------------------------------------------------------+
| HH HH HH HH HH HH HH HH |<-+
+----------------------------------------------------------------+ |
+----------------------------------------------------------------+ |
| HH HH HH HH HH HH HH HH | |
+----------------------------------------------------------------+ |
| | | | | | | | | | | | | | | | |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
^ |
| |
| ---------- --------------------- |
+----- 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.
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Connecting to Spine
|| || || || || || || ||
+----------------------------------------------------------------+ N
| PoD top Node seen sideways | ^
+----------------------------------------------------------------+ |
|| || || || || || || || *
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
| | | | | | | | | | | | | | | | v
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ S
|| || || || || || || ||
Connecting to Client nodes
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
Note 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 is critical at this junction that the concept and the picture of
those "crossed crossbars" is clear before progressing further,
otherwise following considerations will be difficult to comprehend.
Further, the PoDs are interconnected with one another through a Top-
of-Fabric 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 is also
referred to as a single plane configuration. In order to reach a
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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 takes (P * K_LEAF) ports on a ToF node to
connect to each of the K_LEAF ToP nodes of the P PoDs, as illustrated
in Figure 9.
[ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] <-----+
| | | | | | | | |
[=================================] | -----------
| | | | | | | | +----- Top-of-Fabric
[ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] +----- Node -------+
| ----------- |
| v
+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ <-----+ +-+
| | | | | | | | | | | | | | | | | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] ------------------------- | |
[ |H| |H| |H| |H| |H| |H| |H| |H<--- Physical Port (Ethernet) | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] ------------------------- | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | |
| | | | | | | | | | | | | | | | | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] -------------- | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] <--- PoD top level | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] node (Spine) ---+ | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] -------------- | | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | | |
| | | | | | | | | | | | | | | | -+ +- +-+ v | |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | | --| |--[ ]--| |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | ----- | --| |--[ ]--| |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] +--- PoD ---+ --| |--[ ]--| |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | ----- | --| |--[ ]--| |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | | --| |--[ ]--| |
[ |H| |H| |H| |H| |H| |H| |H| |H| ] | | --| |--[ ]--| |
| | | | | | | | | | | | | | | | -+ +- +-+ | |
+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+
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. So we can show one PoD
as a class of PoDs and hence save one dimension in our
representation. The Spine Node expands in the depth and the vertical
dimensions whereas the PoD top level Nodes are constrained in
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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.
/ / / / / / / / / / / / / / / /
/ / / / / / / / / / / / / / / /
/ / / / / / / / / / / / / / / /
/ / / / / / / / / / / / / / / / ]
+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ ]]
| | | | | | | | | | | | | | | | ] ---------------------------
[ |H| |H| |H| |H| |H| |H| |H| |H| ] <-- PoD top level node (Spine)
[ |H| |H| |H| |H| |H| |H| |H| |H| ] ---------------------------
[ |H| |H| |H| |H| |H| |H| |H| |H| ]]]]
[ |H| |H| |H| |H| |H| |H| |H| |H| ]]] ^^
[ |H| |H| |H| |H| |H| |H| |H| |H| ]] // PoDs
[ |H| |H| |H| |H| |H| |H| |H| |H| ] // (in depth)
| |/| |/| |/| |/| |/| |/| |/| |/ //
+-+ +-+ +-+/+-+/+-+ +-+ +-+ +-+ //
^
| ----------------
+----- Top-of-Fabric Node
----------------
Figure 10: Collapsed Northern View of a Fabric for Any Number of PoDs
This type of deployment introduces a "single plane limit" where the
bound is the available radix of the ToF nodes, which limits (P *
K_LEAF). Nevertheless, a distinct advantage of a connected or
unpartitioned Top-of-Fabric is that all failures can be resolved by
simple, non-transitive, positive disaggregation described in
Section 5.2.5.1 that propagates only within one level of the fabric.
In other words unpartitoned ToF nodes can always reach nodes below or
withdraw the routes from PoDs they cannot reach unambiguously. To be
more precise, all failures which still allow all the ToF nodes to see
each other via south reflection as explained in Section 5.2.5.
In order to scale beyond the "single plane limit", the Top-of-Fabric
can be partitioned by a number N of identically wired planes, N being
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
divisor of K_LEAF, then (N=K_LEAF/R) is a feasible number of planes
and R a redundancy factor. If 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,
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meaning that there are 3 non-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 PoD-ToP nodes (spines)
in each PoD.
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
Plane 1
----------- . ------------ . ------------ . ------------ . --------
Plane 2
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
^
|
| ----------------
+----- Top-of-Fabric node
"across" depth
----------------
Figure 11: Northern View of a Multi-Plane ToF Level, K_LEAF=6, N=2
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 and the number of ports required on the Spine Node is more
or equal to P, the number of PoDs.
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Plane 1
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ -+
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
----------- . ------------ . ------------ . ------------ . -------- |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
----------- . ------------ . ------------ . ------------ . -------- |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
----------- . ------------ . ------------ . ------------ . -------- +<-+
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | |
----------- . ------------ . ------------ . ------------ . -------- | |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | |
----------- . ------------ . ------------ . ------------ . -------- | |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ -+ |
Plane 6 ^ |
| |
| ---------------- -------------- |
+----- ToF Node Class of PoDs ---+
---------------- -------------
Figure 12: Northern View of a Maximally Partitioned ToF Level, R=1
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5.1.3. 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 described in Section 5.2.5.1. In
large fabrics or fabrics built from switches with low radix, the ToF
ends often being partioned 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.
We define a "Fallen Leaf" as a leaf that can be reached by only a
subset of Top-of-Fabric nodes but cannot be reached by all 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 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.
On the other hand, there is a need to disaggregate the routes to
Fallen Leaves in a transitive fashion 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
flooding of N-TIEs from the ToP nodes, but the ToF nodes 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
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of N-TIEs from the affected Leaf nodes, together with non-node
N-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, and 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 that 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 -
all leaves fall. Since the Southern Reflection between the ToF
nodes happens only within a plane, ToF nodes in other planes
cannot discover the case of fallen leaves in a different plane,
and cannot determine beyond their local plane whether a Leaf node
that was initially reachable has become unreachable. As above,
the breakage can be observed by the ToF nodes in the plane where
the breakage happened, and then again, 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 N-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.
For the sake of easy comprehension let us roll the abstractions back
to a simple example and observe 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 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:
o Leaf111 trying to route to Leaf122 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
tie'ing, i.e. this information must be in its routing table.
o any kind of "flooding" or distance vector trying to deal with the
problem by distributing host routes will be able to converge only
using paths through leafs, i.e. the flooding of information on
Leaf122 will go up to Top-of-Fabric A and then "loopback" over
other leafs to ToF B leading in extreme cases to traffic for
Leaf122 when presented to plane B taking an "inverted fabric" path
where leafs start to serve as TOFs.
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5.1.4. Discovering Fallen Leaves
As we illustrate later and without further proof here, to deal with
fallen leafs in multi-plane designs when aggregation is used RIFT
requires all the ToF nodes to share the same topology database. This
happens naturally in single plane design but needs additional
considerations in multi-plane fabrics. To satisfy this RIFT in
multi-plane designs relies at the ToF Level on ring interconnection
of switches in multiple planes. Other solutions are possible but
they either need more cabling or end up having much longer flooding
path and/or single points of failure.
In more detail, by reserving two ports on each Top-of-Fabric node it
is possible to connect them together in an interplane bi-directional
ring as illustrated in Figure 13 (where we show a bi-directional ring
connecting switches across planes). The rings will exchange full
topology information between planes and with that allow consequently
by the means of transitive, negative disaggregation described in
Section 5.2.5.2 to efficiently fix any possible fallen leaf scenario.
Somewhat as a side-effect, the exchange of information fulfills the
requirement to present full view of the fabric topology at the Top-
of-Fabric level without the need to collate it from multiple points
by additional complexity of technologies like [RFC7752].
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+----+ +----+ +----+ +----+ +----+ +----+ +--------+
| | | | | | | | | | | | | |
| | | | | | | |
+-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ |
+-| |--| |--| |--| |--| |--| |--| |-+ |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | Plane A
+-| |--| |--| |--| |--| |--| |--| |-+ |
+-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ |
| | | | | | | |
+-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ |
+-| |--| |--| |--| |--| |--| |--| |-+ |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | Plane B
+-| |--| |--| |--| |--| |--| |--| |-+ |
+-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ |
| | | | | | | |
... |
| | | | | | | |
+-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ |
+-| |--| |--| |--| |--| |--| |--| |-+ |
| | HH | | HH | | HH | | HH | | HH | | HH | | HH | | | Plane X
+-| |--| |--| |--| |--| |--| |--| |-+ |
+-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ +-o--+ |
| | | | | | | |
| | | | | | | | | | | | | |
+----+ +----+ +----+ +----+ +----+ +----+ +--------+
Figure 13: Connecting Top-of-Fabric Nodes Across Planes by Two Rings
5.1.5. 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 proposes two methods to address this issue, the positive
and the negative disaggregation. Both methods flood S-TIEs to
advertise the impacted prefix(es).
When used for the operation of disaggregation, a positive S-TIE, as
usual, indicates reachability to a prefix of given length and all
addresses subsumed by it. In contrast, a negative route
advertisement 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,
meaning that the receiver does not generate its own flooding south as
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a consequence of receiving positive disaggregation advertisements
from an higher level node. The effect of a positive disaggregation
is that the traffic to the impacted prefix will follow the prefix
longest match and will be limited to the northbound routers that
advertised the more specific route.
In contrast, the negative disaggregation is transitive, and is
propagated south when all the possible routes northwards are barred.
A negative route advertisement is only actionable when the negative
prefix is aggregated by a positive route advertisement for a shorter
prefix. In that case, the negative advertisement carves an exception
to the positive route in the routing table (one could think of
"punching a hole"), making the positive prefix reachable through the
originator with the special consideration of the negative prefix
removing certain next hop neighbors.
When the ToF is not partitioned, the collective southern 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 leafs in an optimal way is specified in
Section 5.2.5.2.
5.2. Specification
5.2.1. Transport
All packet formats are defined in Thrift [thrift] models in
Appendix B.
The serialized model is carried in an envelope within a UDP frame
that provides security and allows validation/modification of several
important fields without de-serialization for performance and
security reasons.
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5.2.2. Link (Neighbor) Discovery (LIE Exchange)
LIE exchange happens over well-known administratively locally scoped
and configured or otherwise well-known IPv4 multicast address
[RFC2365] and/or link-local multicast scope [RFC4291] for IPv6
[RFC8200] using a configured or otherwise a well-known destination
UDP port defined in Appendix D.1. LIEs SHOULD be sent with a TTL of
1 to prevent RIFT information reaching beyond a single L3 next-hop in
the topology. LIEs SHOULD be sent with network control precedence.
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 negotiation independent on
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 CAN use
any of the adjacency's source addresses it saw in LIEs on the
specific interface during adjacency formation to send TIEs. That
implies that an implementation MUST be ready to accept TIEs on all
addresses it used as source of LIE frames.
A three way adjacency over any address family implies support for
IPv4 forwarding if the `v4_forwarding_capable` flag is set to true
and a node can use [RFC5549] type of forwarding in such a situation.
It is expected that the whole fabric supports the same type of
forwarding of address families on all the links. Operation of a
fabric where only some of the links are supporting forwarding on an
address family and others do not is outside the scope of this
specification.
Observe further that the protocol does NOT support selective
disabling of address families, disabling v4 forwarding capability or
any local address changes in three way state, i.e. if a link has
entered three way 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 v4 forwarding, it has to tear down and
rebuild the adjacency. It also has to remove any information it
stored about the adjacency such as LIE source addresses seen.
Unless Section 5.2.7 is used, each node is provisioned with the level
at which it is operating and its PoD (or otherwise a default level
and "undefined" PoD are assumed; meaning that leafs do not need to be
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configured at all if initial configuration values are all left at 0).
Nodes in the spine are configured with "any" PoD which has the same
value "undefined" PoD hence we will talk about "undefined/any" PoD.
This information is propagated in the LIEs exchanged.
Further definitions of leaf flags are found in Section 5.2.7 given
they have implications in terms of level and adjacency forming here.
A node tries to form a three way adjacency if and only if
1. the node is in the same PoD or either the node or the neighbor
advertises "undefined/any" PoD membership (PoD# = 0) AND
2. the neighboring node is running the same MAJOR schema version AND
3. the neighbor is not member of some PoD while the node has a
northbound adjacency already joining another PoD AND
4. the neighboring node uses a valid System ID AND
5. the neighboring node uses a different System ID than the node
itself
6. the advertised MTUs match on both sides AND
7. both nodes advertise defined level values AND
8. [
i) the node is at level 0 and has no three way adjacencies
already to HAT nodes with level different than the adjacent
node OR
ii) the node is not at level 0 and the neighboring node is at
level 0 OR
iii) both nodes are at level 0 AND both indicate support for
Section 5.3.9 OR
iv) neither node is at level 0 and the neighboring node is at
most one level away
].
The rule in Paragraph 3 MAY be optionally disregarded by a node if
PoD detection is undesirable or has to be ignored.
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A node configured with "undefined" PoD membership MUST, after
building first northbound three way adjacencies to a node being in a
defined PoD, advertise that PoD as part of its LIEs. In case that
adjacency is lost, from all available northbound three way
adjacencies the node with the highest System ID and defined PoD is
chosen. That way the northmost defined PoD value (normally the top
spines in a PoD) can diffuse southbound towards the leafs "forcing"
the PoD value on any node with "undefined" PoD.
LIEs arriving with a TTL larger than 1 MUST be ignored.
A node SHOULD NOT send out LIEs without defined level in the header
but in certain scenarios it may be beneficial for trouble-shooting
purposes.
LIE exchange uses three way handshake mechanism which is a cleaned up
version of [RFC5303]. Observe that for easier comprehension the
terminology of one/two and three-way states does NOT align with OSPF
or ISIS FSMs albeit they use roughly same mechanisms.
5.2.3. Topology Exchange (TIE Exchange)
5.2.3.1. Topology Information Elements
Topology and reachability information in RIFT is conveyed by the
means of TIEs which have good amount of commonalities with LSAs in
OSPF.
The TIE exchange mechanism uses the port indicated by each node in
the LIE exchange and the interface on which the adjacency has been
formed as destination. It SHOULD use TTL of 1 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 a node or deployment 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.
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5.2.3.2. South- and Northbound 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/sideways. We call those differing TIE
databases either south- or northbound (S-TIEs and N-TIEs) depending
on the direction of distribution.
The N-TIEs hold all of the node's adjacencies and local prefixes
while the S-TIEs hold only all of the node's adjacencies, the default
prefix with necessary disaggregated prefixes and local prefixes. We
will explain this in detail further in Section 5.2.5.
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.
+-------------------+-----------------------------------------------+
| TIE-Type | Content |
+-------------------+-----------------------------------------------+
| Node N-TIE | node properties and adjacencies |
+-------------------+-----------------------------------------------+
| Node S-TIE | same content as node N-TIE |
+-------------------+-----------------------------------------------+
| Prefix N-TIE | contains nodes' directly reachable prefixes |
+-------------------+-----------------------------------------------+
| Prefix S-TIE | contains originated defaults and directly |
| | reachable prefixes |
+-------------------+-----------------------------------------------+
| Positive | contains disaggregated prefixes |
| Disaggregation | |
| S-TIE | |
+-------------------+-----------------------------------------------+
| Negative | contains special, negatively disaggreagted |
| Disaggregation | prefixes to support multi-plane designs |
| S-TIE | |
+-------------------+-----------------------------------------------+
| External Prefix | contains external prefixes |
| N-TIE | |
+-------------------+-----------------------------------------------+
| Key-Value N-TIE | contains nodes northbound KVs |
+-------------------+-----------------------------------------------+
| Key-Value S-TIE | contains nodes southbound KVs |
+-------------------+-----------------------------------------------+
Table 2: TIE Types
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As an example illustrating a databases holding both representations,
consider 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). This example assumes unnumbered interfaces. First,
here are the TIEs generated by some nodes. For simplicity, the key
value elements which may be included in their S-TIEs or N-TIEs are
not shown.
Spine21 S-TIEs:
Node S-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 S-TIE:
SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1))
Spine 111 S-TIEs:
Node S-TIE:
NodeElement(level=1, neighbors((Spine21, level 2, cost 1, links(...)),
(Spine22, 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 S-TIE:
SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1))
Spine 111 N-TIEs:
Node N-TIE:
NodeElement(level=1,
neighbors((Spine21, level 2, cost 1, links(...)),
(Spine22, 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 N-TIE:
NorthPrefixesElement(prefixes(Spine 111.loopback)
Spine 121 S-TIEs:
Node S-TIE:
NodeElement(level=1, neighbors((Spine21,level 2,cost 1),
(Spine22, level 2, cost 1), (Leaf121, level 0, cost 1),
(Leaf122, level 0, cost 1)))
Prefix S-TIE:
SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1))
Spine 121 N-TIEs:
Node N-TIE:
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NodeElement(level=1,
neighbors((Spine21, level 2, cost 1, links(...)),
(Spine22, level 2, cost 1, links(...)),
(Leaf121, level 0, cost 1, links(...)),
(Leaf122, level 0, cost 1, links(...))))
Prefix N-TIE:
NorthPrefixesElement(prefixes(Spine 121.loopback)
Leaf112 N-TIEs:
Node N-TIE:
NodeElement(level=0,
neighbors((Spine 111, level 1, cost 1, links(...)),
(Spine 112, level 1, cost 1, links(...))))
Prefix N-TIE:
NorthPrefixesElement(prefixes(Leaf112.loopback, Prefix112,
Prefix_MH))
Figure 14: example TIES generated in a 2 level spine-and-leaf
topology
5.2.3.3. Flooding
The mechanism used to distribute TIEs is the well-known (albeit
modified in several respects to address fat tree requirements)
flooding mechanism used by today's link-state protocols. Although
flooding is initially more demanding to implement it avoids many
problems with update style used in diffused computation such as
distance vector protocols. Since flooding tends to present an
unscalable burden in large, densely meshed topologies (fat trees
being unfortunately such a topology) we provide as solution a close
to optimal global flood reduction and load balancing optimization in
Section 5.2.3.9.
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 equivalent OSPF case.
On reception of a TIE with an undefined level value in the packet
header the node SHOULD issue a warning and indiscriminately discard
the packet.
Precise finite state machines and procedures can be found in
Appendix C.3.
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5.2.3.4. 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 N-TIE is flooded northbound, providing a node at a given level
with the complete topology of the Clos or Fat Tree network underneath
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 may 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 S-TIEs, consisting of all node's adjacencies and prefix
S-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 S-TIEs of other
nodes at its level, every *NODE* S-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 5.2.4. In
that way nodes at same level can learn about each other without a
lower level, e.g. in case of leaf level. The precise flooding scopes
are given in Table 3. Those rules govern as well what SHOULD be
included in TIDEs on the adjacency. Again, East-West flooding scopes
are identical to South flooding scopes except in case of ToF East-
West links (rings) which are basically performing northbound
flooding.
Node S-TIE "south reflection" allows to support positive
disaggregation on failures describes in Section 5.2.5 and flooding
reduction in Section 5.2.3.9.
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+-----------+---------------------+---------------+-----------------+
| Type / | South | North | East-West |
| Direction | | | |
+-----------+---------------------+---------------+-----------------+
| node | flood if level of | flood if | flood only if |
| S-TIE | originator is equal | level of | this node is |
| | to this node | originator is | not ToF |
| | | higher than | |
| | | this node | |
+-----------+---------------------+---------------+-----------------+
| non-node | flood self- | flood only if | flood only if |
| S-TIE | originated only | neighbor is | self-originated |
| | | originator of | and this node |
| | | TIE | is not ToF |
+-----------+---------------------+---------------+-----------------+
| all | never flood | flood always | flood only if |
| N-TIEs | | | this node is |
| | | | ToF |
+-----------+---------------------+---------------+-----------------+
| TIDE | include at least | include at | if this node is |
| | all non-self | least all | ToF then |
| | originated N-TIE | node S-TIEs | include all |
| | headers and self- | and all | N-TIEs, |
| | originated S-TIE | S-TIEs | otherwise only |
| | headers and node | originated by | self-originated |
| | S-TIEs of nodes at | peer and all | TIEs |
| | same level | N-TIEs | |
+-----------+---------------------+---------------+-----------------+
| TIRE as | request all N-TIEs | request all | if this node is |
| Request | and all peer's | S-TIEs | ToF then apply |
| | self-originated | | North scope |
| | TIEs and all node | | rules, |
| | S-TIEs | | otherwise South |
| | | | scope rules |
+-----------+---------------------+---------------+-----------------+
| TIRE as | Ack all received | Ack all | Ack all |
| Ack | TIEs | received TIEs | received TIEs |
+-----------+---------------------+---------------+-----------------+
Table 3: Flooding Scopes
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,
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and the associated TIEs given in Figure 14. The flooding from
particular nodes of the TIEs is given in Table 4.
+-------------+----------+------------------------------------------+
| Router | Neighbor | TIEs |
| floods to | | |
+-------------+----------+------------------------------------------+
| Leaf111 | Spine | Leaf111 N-TIEs, Spine 111 node S-TIE |
| | 112 | |
| Leaf111 | Spine | Leaf111 N-TIEs, Spine 112 node S-TIE |
| | 111 | |
| | | |
| Spine 111 | Leaf111 | Spine 111 S-TIEs |
| Spine 111 | Leaf112 | Spine 111 S-TIEs |
| Spine 111 | Spine | Spine 111 S-TIEs |
| | 112 | |
| Spine 111 | Spine21 | Spine 111 N-TIEs, Leaf111 N-TIEs, |
| | | Leaf112 N-TIEs, Spine22 node S-TIE |
| Spine 111 | Spine22 | Spine 111 N-TIEs, Leaf111 N-TIEs, |
| | | Leaf112 N-TIEs, Spine21 node S-TIE |
| | | |
| ... | ... | ... |
| Spine21 | Spine | Spine21 S-TIEs |
| | 111 | |
| Spine21 | Spine | Spine21 S-TIEs |
| | 112 | |
| Spine21 | Spine | Spine21 S-TIEs |
| | 121 | |
| Spine21 | Spine | Spine21 S-TIEs |
| | 122 | |
| ... | ... | ... |
+-------------+----------+------------------------------------------+
Table 4: Flooding some TIEs from example topology
5.2.3.5. 'Flood Only Node TIEs' Bit
RIFT includes an optional ECN mechanism to prevent "flooding inrush"
on restart or bring-up with many southbound neighbors. A node MAY
set on its LIEs the according bit to indicate to the neighbor that it
should temporarily flood node TIEs only to it. It should only set it
in the southbound direction. The receiving node SHOULD accomodate
the request to lessen the flooding load on the affected node if south
of the sender and SHOULD ignore the bit if northbound.
Obviously this mechanism is most useful in southbound direction. The
distribution of node TIEs guarantees correct behavior of algorithms
like disaggregation or default route origination. Furthermore
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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 will lead to blackholes.
5.2.3.6. Initial and Periodic Database Synchronization
The initial exchange of RIFT is modeled after ISIS with TIDE being
equivalent to CSNP and TIRE playing the role of PSNP. The content of
TIDEs and TIREs is governed by Table 3.
5.2.3.7. Purging and Roll-Overs
RIFT does not purge information that has been distributed by the
protocol. Purging mechanisms in other routing protocols have proven
to be complex and fragile over many years of experience. Abundant
amounts of memory are available today even on low-end platforms. The
information will age out and all computations will deliver correct
results if a node leaves the network due to the new information
distributed by its adjacent nodes.
Once a RIFT node issues a TIE with an ID, it MUST 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 reasonbly unpredictable random number in the
interval [0, 2^10-1] which will prevent otherwise identical TIE
headers to remain "stuck" in the network with content different from
TIE originated after reboot.
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5.2.3.8. Southbound Default Route Origination
Under certain conditions nodes issue a default route in their South
Prefix TIEs with costs as computed in Section 5.3.6.1.
A node X that
1. is NOT overloaded AND
2. has southbound or East-West adjacencies
originates in its south prefix TIE such a default route IIF
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 S-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 MUST install a default
discard route if it did not compute a default route during N-SPF.
5.2.3.9. Northbound TIE Flooding Reduction
Section 1.4 of the Optimized Link State Routing Protocol [RFC3626]
(OLSR) introduces the concept of a "multipoint relay" (MPR) that
minimize the overhead of flooding messages in the network by reducing
redundant retransmissions in the same region.
A similar technique is applied to RIFT to control northbound
flooding. Important observations first:
1. a node MUST flood self-originated N-TIEs to all the reachable
nodes at the level above which we call the node's "parents";
2. it is typically not necessary that all parents reflood the N-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
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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;
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
S-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
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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.
This specification proposes a simple default algorithm that SHOULD be
implemented and used by default on every RIFT node.
o let |NA(Node) be the set of Northbound adjacencies of node Node
and CN(Node) be the cardinality of |NA(Node);
o let |SA(Node) be the set of Southbound adjacencies of node Node
and CS(Node) be the cardinality of |SA(Node);
o let |P(Node) be the set of node Node's parents;
o let |G(Node) be the set of node Node's grandparents. Observe
that |G(Node) = |P(|P(Node));
o let N be the child node at level L computing a set of FR;
o let P be a node at level L+1 and a parent node of N, i.e. bi-
directionally reachable over adjacency A(N, P);
o 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 A(P, G);
o let R be a redundancy constant integer; a value of 2 or higher for
R is RECOMMENDED;
o 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.
o 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:
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(W1<<1) xor (W2<<2) xor (W3<<3) xor (W4<<4);
where << is the circular shift operator.
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):
1. set k=0; // k is the ID of the subarrray
2. set i=0;
3. while i < CN(N) do
1. set j=i;
2. while i < CN(N) and CN(|A(N)[j]) - CN(|A(N)[i]) <= S
1. place |A(N)[i] in |A_k(N) // abstract action, maybe
noop
2. set i=i+1;
3. /* 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) */
4. set k=k+1;
4. /* 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:
1. while k > 0 do
1. for i from C_k(N)-1 to 1 decrementing by 1 do
1. set j to PR(N) modulo i;
2. exchange |A_k[j] and |A_k[i];
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2. set k=k-1;
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):
1. 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:
1. for each P in reshuffled |A(N);
1. if there exists an adjacency ADJ(P, G) in |NA(P) such
that c(G) < R then
1. place P in FR set;
2. for all adjacencies ADJ(P, G') in |NA(P) increment
c(G')
2. 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 S-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. A node SHOULD send out LIEs that grant flood repeater status
before LIEs that revoke it on flood repeater set changes to
prevent transient behavior where the full coverage of grand
parents is not guaranteed. Albeit the condition will correct in
positively stable manner due to LIE retransmission and periodic
TIDEs, it can slow down flooding convergence on flood repeater
status changes.
3. A node always floods its self-originated TIEs.
4. A node receiving a TIE originated by a node for which it is not a
flood repeater does NOT re-flood such TIEs to its neighbors
except for rules in Paragraph 6.
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5. The indication of flood reduction capability is carried in the
node TIEs and can 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 first request ONLY.
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 should load-balance the
incoming database between adjacent nodes and flood repeaters
should guarantee that two copies are sent by different nodes to
ensure against any losses.
7. Obviously sine flooding reduction does NOT apply to self
originated TIEs and since all policy-guided information consists
of self-originated TIEs those are unaffected.
5.2.3.10. 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 they belong.
Since flooding can begin before ZTP is "finished" and in fact must do
so given there is no global termination criteria, information may end
up in wrong layers. A special clause when changing level takes care
of that.
More difficult is a condition where a node floods a TIE north towards
a super-spine, then its spine reboots, in fact partitioning
superspine from it directly and then the node itself reboots. That
leaves in a sense the super-spine holding the "primary copy" of the
node's TIE. Normally this condition is resolved easily by the node
re-originating its TIE with a higher sequence number than it sees in
northbound TIEs, here however, when spine comes back it won't be able
to obtain a N-TIE from its superspine easily and with that the node
below may issue the same version of the TIE with a lower sequence
number. Flooding procedures are 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.
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5.2.4. Reachability Computation
A node has three sources of relevant information. A node knows the
full topology south from the received N-TIEs. A node has the set of
prefixes with associated distances and bandwidths from received
S-TIEs.
To compute reachability, a node runs conceptually a northbound and a
southbound SPF. We call that N-SPF and S-SPF.
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 but we use simple, familiar SPF
algorithms and concepts here due to their prevalence in today's
routing.
5.2.4.1. Northbound SPF
N-SPF uses northbound and East-West adjacencies in the computing
node's node N-TIEs (since if the node is a leaf it may not have
generated a node S-TIE) when starting Dijkstra. Observe that N-SPF
is really just a one hop variety since Node S-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, we are using the next level's node S-TIEs to find
according adjacencies to verify backlink connectivity. Just as in
case of IS-IS or OSPF, two unidirectional links are associated
together to confirm bidirectional connectivity. Particular care MUST
be paid that the Node TIEs do not only contain the correct system IDs
but matching levels as well.
Default route found when crossing an E-W link is used IIF
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 IIF
1. no north neighbors are advertising same or supersuming non-
default prefix AND
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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 de-aggregation in pathological fabric
partitioning scenarios.
A detailed example can be found in Section 6.4.
5.2.4.2. Southbound SPF
S-SPF uses only the southbound adjacencies in the node S-TIEs, i.e.
progresses towards nodes at lower levels. Observe that E-W
adjacencies are NEVER used in the computation. This enforces the
requirement that a packet traversing in a southbound direction must
never change its direction.
S-SPF uses northbound adjacencies in node N-TIEs to verify backlink
connectivity.
5.2.4.3. East-West Forwarding Within a non-ToF Level
Ultimately, it should be observed that in presence of a "ring" of E-W
links in any level (except ToF level) neither SPF will provide a
"ring protection" scheme since such a computation would have to deal
necessarily with breaking of "loops" in generic Dijkstra sense; an
application for which RIFT is not intended. It is outside the scope
of this document how an underlay can be used to provide a full-mesh
connectivity between nodes in the same level that would allow for
N-SPF to provide protection for a single node loosing all its
northbound adjacencies (as long as any of the other nodes in the
level are northbound connected).
Using south prefixes over horizontal links is optional and 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.
5.2.4.4. East-West Links Within ToF Level
E-W ToF links behave in terms of flooding scopes defined in
Section 5.2.3.4 like northbound links. Even though a ToF node could
be tempted to use those links during southbound SPF this MUST NOT be
attempted since it may lead in, e.g. anycast cases to routing loops.
An implemention could 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
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capacity provisioning of such links when they become traffic-bearing
in case of failures is vexing.
5.2.5. Automatic Disaggregation on Link & Node Failures
5.2.5.1. Positive, Non-transitive Disaggregation
Under normal circumstances, node's S-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 S-TIE.
Otherwise, some percentage of the northbound traffic for those
prefixes would be sent to nodes without according reachability,
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.
We refer to the process of advertising additional prefixes southbound
as 'positive de-aggregation' or 'positive dis-aggregation'. Such
dis-aggregation 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 dis-aggregation necessary to prevent looping or bow-tying
the fabric.
A node determines the set of prefixes needing de-aggregation using
the following steps:
1. A DAG computation in the southern direction is performed first,
i.e. the N-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, we define its set of next-hops to
be |H(r).
2. The node uses reflected S-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, we define its set of southbound adjacencies
to be |A(n).
3. For a given r, if the intersection of |H(r) and |A(n), for any n,
is null then that prefix r must be explicitly advertised by the
node in an S-TIE.
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4. Identical set of de-aggregated prefixes is flooded on each of the
node's southbound adjacencies. In accordance with the normal
flooding rules for an S-TIE, a node at the lower level that
receives this S-TIE will not propagate it south-bound. Neither
is it necessary for the receiving node to 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,
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 6.3.
A possible algorithm is described last:
1. Create partial_neighbors = (empty), a set of neighbors with
partial connectivity to the node X's level from X's perspective.
Each entry is a list of 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 S-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 to
disaggregate any prefixes. If node X is advertising
disaggregated prefixes in its S-TIE, X SHOULD remove them and re-
advertise its according S-TIEs.
A node X computes reachability to all nodes below it based upon the
received N-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 S-TIE
if (S-TIE.level == X.level and
X shares at least one S-neighbor with X)
add S-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 S-TIE
if X's S-TIE is different
schedule S-TIE for flooding
end if
Figure 15: Computation of Disaggregated Prefixes
Each disaggregated prefix is sent with the according path_distance.
This allows a node to send the same S-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 5.3.1 have to be respected
during the computation.
3. all the lower level nodes are flooded the same disaggregated
prefixes since we don't want to build an S-TIE per node and
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complicate things unnecessarily. The PoD containing the prefix
will prefer southbound anyway.
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 S-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. An implementation MAY hence
choose different strategies to address this behavior if needed.
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 5.1.2 or in other terms, it takes at
minimum that many link failures to partition the ToF into multiple
planes.
5.2.5.2. Negative, Transitive Disaggregation for Fallen Leafs
As explained in Section 5.1.3 failures in multi-plane Top-of-Fabric
or more than (K_LEAF * P) links failing in single plane design can
generate fallen leafs. Such scenario cannot be addressed by positive
disaggregation only and needs a further mechanism.
5.2.5.2.1. Cabling of Multiple Top-of-Fabric Planes
Let us return in this section to designs with multiple planes as
shown in Figure 3. Figure 16 highlights how the ToF is cabled in
case of two planes by the means of dual-rings to distribute all the
N-TIEs within both planes. For people familiar with traditional
link-state routing protocols ToF level can be considered equivalent
to area 0 in OSPF or level-2 in ISIS which need to be "connected" as
well for the protocol to operate correctly.
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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 16: Topologically connected planes
As described in Section 5.1.3 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.
5.2.5.2.2. Transitive Advertisement of Negative Disaggregates
A ToF node that discovers that it cannot reach a fallen leaf
disaggregates all the prefixes of such leafs. It uses for that
purpose negative prefix S-TIEs that are, as usual, flooded southwards
with the scope defined in Section 5.2.3.4.
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
leafs 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.
5.2.5.2.3. 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. We
describe them consecutively.
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The first origination reason is a computation that uses all the node
N-TIEs to build the set of all reachable nodes by reachability
computation over the complete graph and including 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 5.2.4.2.
The difference are the fallen leafs and all their attached prefixes
are advertised as negative prefixes southbound if the node does not
see the prefix being reachable within southbound SPF.
The second mechanism hinges on the understanding how the negative
prefixes are used within the computation as described in Figure 17.
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.
5.2.6. 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 N-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 S-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 S-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
S-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 5.3.3
necessary. Then each prefix can be added into the RIFT route
database with the next_hop_set; ties are broken based upon type first
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and then distance and further attributes 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 S-TIE
if S-TIE.level > X.level
next_hop_set = set of minimum cost links to the S-TIE.originator
next_hop_cost = minimum cost link to S-TIE.originator
end if
for each prefix P in the S-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 17: Adding Routes from S-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
prefix that aggregates it, and subsequently adjacencies to nodes that
advertised negative for this prefix are removed.
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.
Similarily, if a nexthop is deleted for a given prefix, then it is
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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 let us consider a ToP node T1 with 4 ToF parents S1..S4 as
represented in Figure 18:
+----+ +----+ +----+ +----+ N
| S1 | | S1 | | S1 | | S1 | ^
+----+ +----+ +----+ +----+ W< + >E
| | | | v
|+--------+ | | S
||+-----------------+ |
|||+----------------+---------+
||||
+----+
| T1 |
+----+
Figure 18: 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
Forwarding table (FIB) retains only the ultimately computed
"positive" routing instructions. In T1, those tables would look as
illustrated in Figure 19:
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+---------+
| Default |
+---------+
|
| +--------+
+---> | Via S1 |
| +--------+
|
| +--------+
+---> | Via S2 |
| +--------+
|
| +--------+
+---> | Via S3 |
| +---------+
|
| +--------+
+---> | Via S4 |
+--------+
Figure 19: 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 20 and Figure 21, respectively:
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+---------+ +-----------------+
| Default | <-------------- | ~2001:db8::/32 |
+---------+ +-----------------+
| |
| +--------+ | +--------+
+---> | Via S1 | +---> | Via S1 |
| +--------+ +--------+
|
| +--------+
+---> | Via S2 |
| +--------+
|
| +--------+
+---> | Via S3 |
| +---------+
|
| +--------+
+---> | Via S4 |
+--------+
Figure 20: 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 21: Abstract FIB after negative 2001:db8::/32 from S1
To illustrate matters further let us 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 22:
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+---------+ +----------------+ +------------------+
| Default | <----- | ~2001:db8::/32 | <------ | ~2001:db8:1::/48 |
+---------+ +----------------+ +------------------+
| | |
| +--------+ | +--------+ |
+---> | Via S1 | +---> | Via S1 | |
| +--------+ +--------+ |
| |
| +--------+ | +--------+
+---> | Via S2 | +---> | Via S2 |
| +--------+ +--------+
|
| +--------+
+---> | Via S3 |
| +---------+
|
| +--------+
+---> | Via S4 |
+--------+
Figure 22: Abstract RIB after negative 2001:db8:1::/48 from S2
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 father with the negative holes "punched in" again.
After the update, the FIB in T1 shows as illustrated in Figure 23:
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+---------+ +---------------+ +-----------------+
| 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 23: Abstract FIB after negative 2001:db8:1::/48 from S2
Further, let us say 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 24.
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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 24: 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, let us look at the case 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 25:
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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 25: Abstract FIB after negative 2001:db8:2::/48 from S4
5.2.7. 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 Top-of-Fabric at the top
of the topology or the must operate in the 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 leafs) tries to attach at the highest
possible point in the fabric. This guarantees that even if the
diffusion front reaches a node from "below" faster than from "above",
it will greedily abandon already negotiated level derived from nodes
topologically below it and properly peers with nodes above.
The fabric is very conciously numbered from the top to allow for PoDs
of different heights and minimize number of provisioning necessary,
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in this case just a TOP_OF_FABRIC flag on every node at the top of
the fabric.
This section describes the necessary concepts and procedures for ZTP
operation.
5.2.7.1. 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 beeen 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 0.
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 5.2.5.2).
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. 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 0.
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 5.3.9. In a
strict sense it is a capability that implies LEAF_ONLY and the
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according restrictions. TOP_OF_FABRIC flag is ignored when set at
the same time as this 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 0 do not constitute VOLs
(since no valid DERIVED_LEVEL can be obtained from those and
consequently `not_a_ztp_offer` 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 Three Way (HAT): Highest neigbhor level of all the
formed three way adjacencies for the node.
5.2.7.2. Automatic SystemID Selection
RIFT nodes require a 64 bit SystemID which SHOULD be derived as
EUI-64 MA-L derive according to [EUI64]. The organizationally
goverened 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) 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 8 are implemented).
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5.2.7.3. Generic Fabric Example
ZTP forces us to think about miscabled or unusually cabled fabric and
how such a topology can be forced into a "lattice" structure which a
fabric represents (with further restrictions). Let us consider a
necessary and sufficient physical cabling in Figure 26. We assume
all nodes being in the same PoD.
. +---+
. | A | s = TOP_OF_FABRIC
. | s | l = LEAF_ONLY
. ++-++ l2l = LEAF_2_LEAF
. | |
. +--+ +--+
. | |
. +--++ ++--+
. | E | | F |
. | +-+ | +-----------+
. ++--+ | ++-++ |
. | | | | |
. | +-------+ | |
. | | | | |
. | | +----+ | |
. | | | | |
. ++-++ ++-++ |
. | I +-----+ J | |
. | | | +-+ |
. ++-++ +--++ | |
. | | | | |
. +---------+ | +------+ |
. | | | | |
. +-----------------+ | |
. | | | | |
. ++-++ ++-++ |
. | X +-----+ Y +-+
. |l2l| | l |
. +---+ +---+
Figure 26: Generic ZTP Cabling Considerations
First, we 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
we have to decide whether node Y is at the same level as I, J or at
the same level as Y and consequently, X is south of it. This is
unresolvable here until we "nail down the bottom" of the topology.
To achieve that we choose to use in this example the leaf flags. We
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will see further then whether Y chooses to form adjacencies to F or
I, J successively.
5.2.7.4. 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:
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 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 three way 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:
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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 5.2.2.
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
fabric" while another layer could "invert" the fabric by picking
its prefered VOL in a different fashion than always trying to
achieve the highest viable level.
5.2.7.5. Resulting Topologies
The procedures defined in Section 5.2.7.4 will lead to the RIFT
topology and levels depicted in Figure 27.
. +---+
. | As|
. | 24|
. ++-++
. | |
. +--+ +--+
. | |
. +--++ ++--+
. | E | | F |
. | 23+-+ | 23+-----------+
. ++--+ | ++-++ |
. | | | | |
. | +-------+ | |
. | | | | |
. | | +----+ | |
. | | | | |
. ++-++ ++-++ |
. | I +-----+ J | |
. | 22| | 22| |
. ++--+ +--++ |
. | | |
. +---------+ | |
. | | |
. ++-++ +---+ |
. | X | | Y +-+
. | 0 | | 0 |
. +---+ +---+
Figure 27: Generic ZTP Topology Autoconfigured
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In case we imagine the LEAF_ONLY restriction on Y is removed the
outcome would be very different however and result in Figure 28.
This demonstrates basically that auto configuration makes miscabling
detection hard and with that can lead to undesirable effects in cases
where leafs 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 0) this can indicate miscabling.
. +---+
. | As|
. | 24|
. ++-++
. | |
. +--+ +--+
. | |
. +--++ ++--+
. | E | | F |
. | 23+-+ | 23+-------+
. ++--+ | ++-++ |
. | | | | |
. | +-------+ | |
. | | | | |
. | | +----+ | |
. | | | | |
. ++-++ ++-++ +-+-+
. | I +-----+ J +-----+ Y |
. | 22| | 22| | 22|
. ++-++ +--++ ++-++
. | | | | |
. | +-----------------+ |
. | | |
. +---------+ | |
. | | |
. ++-++ |
. | X +--------+
. | 0 |
. +---+
Figure 28: Generic ZTP Topology Autoconfigured
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5.2.8. Stability Considerations
The autoconfiguration mechanism computes a global maximum of levels
by diffusion. The achieved equilibrium can be disturbed massively by
all nodes with highest level either leaving or entering the domain
(with some finer distinctions not explained further). It is
therefore recommended that each node is multi-homed towards nodes
with respective HAL offerings. Fortuntately, this is the natural
state of things for the topology variants considered in RIFT.
5.3. Further Mechanisms
5.3.1. Overload Bit
The overload Bit MUST be respected in all according reachability
computations. A node with overload bit set SHOULD NOT advertise any
reachability prefixes southbound except locally hosted ones. A node
in overload SHOULD advertise all its locally hosted prefixes north
and southbound.
The leaf node SHOULD set the 'overload' bit on its node TIEs, since
if the spine nodes were to forward traffic not meant for the local
node, the leaf node does not have the topology information to prevent
a routing/forwarding loop.
5.3.2. Optimized Route Computation on Leafs
Since the leafs do see only "one hop away" they do not need to run a
"proper" SPF. Instead, they can gather the available prefix
candidates from their neighbors and build the routing table
accordingly.
A leaf will have no N-TIEs except its own and optionally from its
East-West neighbors. A leaf will have S-TIEs from its neighbors.
Instead of creating a network graph from its N-TIEs and neighbor's
S-TIEs and then running an SPF, a leaf node can simply compute the
minimum cost and next_hop_set to each leaf neighbor by examining its
local adjacencies, determining bi-directionality from the associated
N-TIE, and specifying the neighbor's next_hop_set set and cost from
the minimum cost local adjacency to that neighbor.
Then a leaf attaches prefixes as described in Section 5.2.6.
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5.3.3. Mobility
It is a requirement for RIFT to maintain at the control plane a real
time status of which prefix is attached to which port of which leaf,
even in a context of mobility where the point of attachement may
change several times in a subsecond period of time.
There are two classical approaches to maintain such knowledge in an
unambiguous fashion:
time stamp: With this method, the infrastructure records 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
to be able to compare time stamps as observed by the various
points of attachment, e.g., using the variation of the Precision
Time Protocol (PTP) IEEE Std. 1588 [IEEEstd1588], [IEEEstd8021AS]
designed for bridged LANs IEEE Std. 802.1AS [IEEEstd8021AS]. Both
the precision of the synchronisation protocol and the resolution
of the time stamp must beat the highest possible roaming time on
the fabric. Another drawback is that the presence of the mobile
device may be observed only asynchronously, e.g., after it starts
using an IP protocol such as ARP [RFC0826], IPv6 Neighbor
Discovery [RFC4861][RFC4862], or DHCP [RFC2131][RFC8415].
sequence counter: With this method, a mobile node 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 movements is kept in order by the device. The
disadvantage of this approach is the lack of support for protocols
that may be used by the mobile node to register its presence to
the leaf node with the capability to provide a sequence counter.
Well-known issues with wrapping sequence counters must be
addressed properly, and many forms of sequence counters that vary
in both wrapping rules and comparison rules. A particular
knowledge of the source of the sequence counter is required to
operate it, and the comparison between sequence counters from
heterogeneous sources can be hard to impossible.
RIFT supports a hybrid approach contained in an optional
`PrefixSequenceType` prefix attribute that we call a `monotonic
clock` consisting of a timestamp and optional sequence number. In
case of presence of the attribute:
o The leaf node MAY advertise a time stamp of the latest sighting of
a prefix, e.g., by snooping IP protocols or the node using the
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time at which it advertised the prefix. RIFT transports the time
stamp within the desired prefix N-TIEs as 802.1AS timestamp.
o RIFT may interoperate with the "update to 6LoWPAN Neighbor
Discovery" [RFC8505], which provides a method for registering a
prefix with a sequence counter called a Transaction ID (TID).
RIFT transports in such case the TID in its native form.
o RIFT also defines an abstract negative clock (ANSC) that compares
as less than any other clock. By default, the lack of a
`PrefixSequenceType` in a Prefix N-TIE is interpreted as ANSC. We
call this also an `undefined` clock.
o Any prefix present on the fabric in multiple nodes that has the
`same` clock is considered as anycast. ASNC is always considered
smaller than any defined clock.
o RIFT implementation assumes by default that all nodes are being
synchronized to 200 milliseconds precision which is easily
achievable even in very large fabrics using [RFC5905]. An
implementation MAY provide a way to reconfigure a domain to a
different value. We call this variable MAXIMUM_CLOCK_DELTA.
5.3.3.1. Clock Comparison
All monotonic clock values are comparable 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].
5.3.3.2. Interaction between Time Stamps and Sequence Counters
For slow movements that occur less frequently than e.g. once per
second, the time stamp that the RIFT infrastruture captures is enough
to determine the freshest discovery. If the point of attachement
changes faster than the maximum drift of the time stamping mechanism
(i.e. MAXIMUM_CLOCK_DELTA), then a sequence counter is required to
add resolution to the freshness evaluation, and it must be sized so
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that the counters stay comparable within the resolution of the time
stampling mechanism.
The sequence counter in [RFC8505] is encoded as one octet and wraps
around using Appendix A.
Within the resolution of MAXIMUM_CLOCK_DELTA the sequence counters
captured during 2 sequential values of the time stamp SHOULD be
comparable. This means with default values that a node may move up
to 127 times during a 200 milliseconds period and the clocks remain
still comparable thus allowing the infrastructure to assert the
freshest advertisement with no ambiguity.
5.3.3.3. 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 prefered. An
anycast prefix does not carry a clock or all clock attributes MUST be
the same under the rules of Section 5.3.3.1.
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.
5.3.3.4. Overlays and Signaling
RIFT is agnostic whether any overlay technology like [MIP, LISP,
VxLAN, NVO3] and the associated signaling is deployed over it. But
it is expected that leaf nodes, and possibly Top-of-Fabric nodes can
perform the correct encapsulation.
In the context of mobility, overlays provide a classical solution to
avoid injecting mobile prefixes in the fabric and improve the
scalability of the solution. It makes sense on a data center that
already uses overlays to consider their applicability to the mobility
solution; as an example, a mobility protocol such as LISP 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
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tunneling from leaf to the Top-of-Fabric may be desired. Future
versions of this document may describe support for such tunneling in
RIFT.
5.3.4. Key/Value Store
5.3.4.1. Southbound
The protocol supports a southbound distribution of key-value pairs
that can be used to e.g. distribute configuration information during
topology bring-up. The KV S-TIEs can arrive from multiple nodes and
hence need tie-breaking per key. We use the following rules
1. Only KV TIEs originated by nodes to which the receiver has a bi-
directional adjacency are considered.
2. Within all such valid KV S-TIEs containing the key, the value of
the KV S-TIE for which the according node S-TIE is present, has
the highest level and within the same level has highest
originating system ID is preferred. If keys in the most
preferred TIEs are overlapping, the behavior is undefined.
Observe that if a node goes down, the node south of it looses
adjacencies to it and with that the KVs will be disregarded and on
tie-break changes new KV re-advertised to prevent stale information
being used by nodes further south. KV information in southbound
direction is not result of independent computation of every node over
same set of TIEs but a diffused computation.
5.3.4.2. Northbound
Certain use cases seem to necessitate distribution of essentialy KV
information that is generated in the leafs in the northbound
direction. Such information is flooded in KV N-TIEs. Since the
originator of northbound KV is preserved during northbound flooding,
overlapping keys could be used. However, to omit further protocol
complexity, only the value of the key in TIE tie-broken in same
fashion as southbound KV TIEs is used.
5.3.5. Interactions with BFD
RIFT MAY incorporate BFD [RFC5881] to react quickly to link failures.
In such case following procedures are introduced:
After RIFT three way 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 on the LIEs.
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In case established BFD session goes Down after it was Up, RIFT
adjacency should be re-initialized started from Init.
In case of parallel links between nodes each link may run its own
independent BFD session or they may share a session.
In case RIFT changes link identifiers or BFD capability indication
both the LIE as well as the BFD sessions SHOULD be brought down
and back up again.
Multiple RIFT instances MAY choose to share a single BFD session
(in such case it is undefined what discriminators are used albeit
RIFT CAN advertise the same link ID for the same interface in
multiple instances and with that "share" the discriminators).
BFD TTL follows [RFC5082].
5.3.6. Fabric Bandwidth Balancing
A well understood problem in fabrics is that in case of link losses
it would be ideal to rebalance how much traffic is offered to
switches in the next level based on the ingress and egress bandwidth
they have. Current attempts rely mostly on specialized traffic
engineering via controller or leafs being aware of complete topology
with according cost and complexity.
RIFT can support a very light weight mechanism that can deal with the
problem in an approximate way based on the fact that RIFT is loop-
free.
5.3.6.1. Northbound Direction
Every RIFT node SHOULD compute the amount of northbound bandwith
available through neighbors at higher level and modify distance
received on default route from this neighbor. Those different
distances SHOULD be used to support weighted ECMP forwarding towards
higher level when using default route. We call such a distance
Bandwidth Adjusted Distance or BAD. This is best illustrated by a
simple example.
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. 100 x 100 100 MBits
. | x | |
. +-+---+-+ +-+---+-+
. | | | |
. |Spin111| |Spin112|
. +-+---+++ ++----+++
. |x || || ||
. || |+---------------+ ||
. || +---------------+| ||
. || || || ||
. || || || ||
. -----All Links 10 MBit-------
. || || || ||
. || || || ||
. || +------------+| || ||
. || |+------------+ || ||
. |x || || ||
. +-+---+++ +--++-+++
. | | | |
. |Leaf111| |Leaf112|
. +-------+ +-------+
Figure 29: Balancing Bandwidth
All links from Leafs in Figure 29 are assumed to 10 MBit/s bandwidth
while the uplinks one level further up are assumed to be 100 MBit/s.
Further, in Figure 29 we assume that Leaf111 lost one of the parallel
links to Spine 111 and with that wants to possibly push more traffic
onto Spine 112. Leaf 112 has equal bandwidth to Spine 111 and Spine
112 but Spine 111 lost one of its uplinks.
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 adjustements.
On a node L use Node TIEs to compute for each non-overloaded
northbound neighbor N three 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
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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 M_N_u.
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 the
understanding. We assume the default route distance is advertised
with D=1 everywhere and 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 5: BAD Computation
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 is only computed for default routes. A node MAY compute and use
BAD for any disaggregated prefixes or other RIFT routes. A node MAY
use another algorithm than BAD to weight northbound traffic based on
bandwidth given that the algorithm is distributed and un-synchronized
and ultimately, its correct behavior does not depend on uniformity of
balancing algorithms used in the fabric. E.g. it is conceivable that
leafs could use real time link loads gathered by analytics to change
the amount of traffic assigned to each default route next hop.
Observe further that a change in available bandwidth will only affect
at maximum two levels down in the fabric, i.e. blast radius of
bandwidth changes is contained no matter its height.
5.3.6.2. Southbound Direction
Due to its loop free properties a node CAN take during S-SPF into
account the available bandwidth on the nodes in lower levels and
modify the amount of traffic offered to next level's "southbound"
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nodes based as what it sees is the total achievable maximum flow
through those nodes. It is worth observing that such computations
may work better if standardized but does not have to be necessarily.
As long the packet keeps on heading south it will take one of the
available paths and arrive at the intended destination.
5.3.7. Label Binding
A node MAY advertise on its TIEs a locally significant, downstream
assigned label for the according interface. One use of such label is
a hop-by-hop encapsulation allowing to easily distinguish forwarding
planes served by a multiplicity of RIFT instances.
5.3.8. Segment Routing Support with RIFT
Recently, alternative architecture to reuse labels as segment
identifiers [RFC8402] has gained traction and may present use cases
in IP fabric that would justify its deployment. Such use cases will
either precondition an assignment of a label per node (or other
entities where the mechanisms are equivalent) or a global assignment
and a knowledge of topology everywhere to compute segment stacks of
interest. We deal with the two issues separately.
5.3.8.1. Global Segment Identifiers Assignment
Global segment identifiers are normally assumed to be provided by
some kind of a centralized "controller" instance and distributed to
other entities. This can be performed in RIFT by attaching a
controller to the Top-of-Fabric nodes at the top of the fabric where
the whole topology is always visible, assign such identifiers and
then distribute those via the KV mechanism towards all nodes so they
can perform things like probing the fabric for failures using a stack
of segments.
5.3.8.2. Distribution of Topology Information
Some segment routing use cases seem to precondition full knowledge of
fabric topology in all nodes which can be performed albeit at the
loss of one of highly desirable properties of RIFT, namely minimal
blast radius. Basically, RIFT can function as a flat IGP by
switching off its flooding scopes. All nodes will end up with full
topology view and albeit the N-SPF and S-SPF are still performed
based on RIFT rules, any computation with segment identifiers that
needs full topology can use it.
Beside blast radius problem, excessive flooding may present
significant load on implementations.
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5.3.9. Leaf to Leaf Procedures
RIFT can optionally allow special leaf East-West adjacencies under
additional set of rules. The leaf supporting those procedures MUST:
advertise the LEAF_2_LEAF flag in node capabilities AND
set the overload bit on all leaf's node TIEs AND
flood only node's own north and south TIEs over E-W leaf
adjacencies AND
always use E-W leaf adjacency in both north as well as south
computation AND
install a discard route for any advertised aggregate in leaf's
TIEs 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).
5.3.10. Address Family and Multi Topology Considerations
Multi-Topology (MT)[RFC5120] and Multi-Instance (MI)[RFC8202] is 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 5.3.5 are implementation dependent when
multiple RIFT instances run on the same link.
5.3.11. Reachability of Internal Nodes in the Fabric
RIFT does not precondition that its nodes have reachable addresses
albeit for operational purposes this is clearly desirable. Under
normal operating conditions this can be easily achieved by e.g.
injecting the node's loopback address into North and South Prefix
TIEs or other implementation specific mechanisms.
Things get more interesting in case a node looses all its northbound
adjacencies but is not at the top of the fabric. That is outside the
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scope of this document and may be covered in a separate document
about policy guided prefixes [PGP reference].
5.3.12. One-Hop Healing of Levels with East-West Links
Based on the rules defined in Section 5.2.4, Section 5.2.3.8 and
given presence of E-W links, RIFT can provide a one-hop protection of
nodes that lost all their northbound links or in other complex link
set failure scenarios except at Top-of-Fabric where the links are
used exclusively to flood topology information in multi-plane
designs. Section 6.4 explains the resulting behavior based on one
such example.
5.4. Security
5.4.1. 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. necessary provisioning
and auto-configuration. At a minimum, in all approaches, the
security of an established adjacency can be ensured. The stricter
the security model the more provisioning must take over the role of
ZTP.
The most security conscious operators will want to have full control
over which port on which router/switch is connected to the respective
port on the "other side", which we will call the "port-association
model" (PAM) achievable e.g. by configuring on each port pair a
designated shared key or pair of private/public keys. In secure data
center locations, operators may want to control which router/switch
is connected to which other router/switch only or choose a "node-
association model" (NAM) which allows, for example, simplified port
sparing. In an even more relaxed environment, an operator may only
be concerned that the router/switches share credentials ensuring that
they belong to this particular data center network hence allowing the
flexible sparing of whole routers/switches. We will define that case
as the "fabric-association model" (FAM), equivalent to using a shared
secret for the whole fabric. Such flexibility may make sense for
leaf nodes such as servers where the addition and swapping of servers
is more frequent than the rest of the data center network.
Generally, leafs of the fabric tend to be less trusted than switches.
The different models could be mixed throughout the fabric if the
benefits outweigh the cost of increased complexity in provisioning.
In each of the above cases, some configuration mechanism is needed to
allow the operator to specify which connections are allowed, and some
mechanism is needed to:
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a. specify the according level in the fabric,
b. discover and report missing connections,
c. discover and report unexpected connections, and prevent such
adjacencies from forming.
On the more relaxed configuration side of the spectrum, operators
might only configure the level of each switch, but don't explicitly
configure which connections are allowed. In this case, RIFT will
only allow adjacencies to come up between nodes are that in adjacent
levels. The operators with lowest security requirements may not use
any configuration to specify which connections are allowed. Such
fabrics could rely fully on ZTP for each router/switch to discover
its level and would only allow adjacencies between adjacent levels to
come up. Figure 30 illustrates the tradeoffs inherent in the
different security models.
Ultimately, some level of verification of the link quality may be
required before an adjacency is allowed to be used for forwarding.
For example, an implementation may require that a BFD session comes
up before advertising the adjacency.
For the above outlined cases, RIFT has two approaches to enforce that
a local port is connected to the correct port on the correct remote
router/switch. 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
configured expected cabling topology, and optionally introduce some
new rules in the FSM to allow the adjacency to come up if the
expectations are met.
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^ /\ |
/|\ / \ |
| / \ |
| / PAM \ |
Increasing / \ Increasing
Integrity +----------+ Flexibility
& / NAM \ &
Increasing +--------------+ Less
Provisioning / FAM \ Configuration
| +------------------+ |
| / Level Provisioning \ |
| +----------------------+ \|/
| / Zero Configuration \ v
+--------------------------+
Figure 30: Security Model
5.4.2. Security Mechanisms
RIFT Security goals are to ensure authentication, message integrity
and prevention of replay attacks. Low processing overhead and
efficient messaging are also a goal. 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 it specifies
how the key can be used to achieve goals.
The protocol has provisions for "weak" nonces to prevent replay
attacks and includes authentication mechanisms comparable to
[RFC5709] and [RFC7987].
5.4.3. Security Envelope
RIFT MUST be carried in a mandatory secure envelope illustrated in
Figure 31. Any value in the packet following a security fingerprint
MUST be used only after the according fingerprint has been validated.
Local configuration MAY allow to skip the checking of the envelope's
integrity.
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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 31: Security Envelope
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RIFT MAGIC: 16 bits. Constant value of 0xA1F7 that allows to
classify RIFT packets independent of used UDP port.
Packet Number: 16 bits. An optional, per packet type monotonically
growing number rolling over using sequence number arithmetic
defined inAppendix 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.
RIFT Major Version: 8 bits. It allows to check whether protocol
versions are compatible, i.e. the serialized object can be decoded
at all. An implementation MUST drop packets with unexpected value
and MAY report a problem. Must be same as in encoded model
object, otherwise packet is dropped.
Outer Key ID: 8 bits to allow key rollovers. This implies key type
and used algorithm. Value 0 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 0 means that no valid fingerprint was computed.
This key ID scope is global to the RIFT instance since it implies
the originator of the TIE so the contained object does not have to
be de-serialized to obtain it.
Length of Fingerprint: 8 bits. Length in 32-bit multiples of the
following fingerprint not including lifetime or weak nonces. It
allows to navigate the structure when an unknown key type is
present. To clarify a common cornercase when this value is set to
0 it signifies an empty (0 bytes long) security fingerprint.
Security Fingerprint: 32 bits * Length of Fingerprint. This is a
signature that is computed over all data following after it. If
the signficant bits of fingerprint are fewer than the 32 bits
padded length than the signficant 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
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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. The value in the serialized
model object MUST be ignored.
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.
5.4.4. Weak Nonces
The protocol uses two 16 bit nonces to salt generated signatures. We
use the term "nonce" a bit loosely since RIFT nonces are not being
changed on every packet as common in cryptography. For efficiency
purposes they are changed at a frequency high enough to dwarf replay
attacks attempts for all practical purposes. Therefore, we call them
"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 SHOULD be incremented again
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 and
MUST increment its nonce at least every 5 minutes (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 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.
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In case where a secure implementation does not receive signatures or
receives undefined nonces from neighbor indicating that it does not
support or verify signatures, it is a matter of local policy how such
packets are treated. Any secure implementation may choose to either
refuse forming an adjacency with an implementation not advertising
signatures or valid nonces or simply keep on signing local packets
while accepting neighbor's packets without further security
verification.
As a necessary exception, an implementation MUST advertise
`undefined_nonce` for remote nonce value when the FSM is not in 2-way
or 3-way state and accept an `undefined_nonce` for its local nonce
value on packets in any other state than 3-way.
As optional optimization, an implemenation MAY send one LIE with
previously negotiated neighbor's nonce to try to speed up a
neighbor's transition from 3-way to 1-way and MUST revert to sending
`undefined_nonce` after that.
5.4.5. Lifetime
Protecting lifetime on flooding may lead to excessive number of
security fingerprint computation and hence an application generating
such fingerprints on TIEs MAY round the value down to the next
`rounddown_lifetime_interval` defined in the schema when sending TIEs
albeit such optimization in presence of security hashes over
advancing weak nonces may not be feasible.
5.4.6. Key Management
As outlined in the Security Model a private shared key or a public/
private key pair is used to Authenticate the adjacency. The actual
method of key distribution and key synchronization is assumed to be
out of band from RIFT's perspective. Both nodes in the adjacency
must share the same keys and configuration of key type and algorithm
for a key ID. Mismatched keys will obviously not inter-operate due
to unverifiable security envelope.
Key roll-over while the adjacency is active is allowed and the
technique is well known and described in e.g. [RFC6518]. Key
distribution procedures are out of scope for RIFT.
5.4.7. 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 and make the changes and then bring the adjacency up.
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Obviously, an implementation may choose to stop verifying security
envelope for the duration of key change to keep the adjacency up but
since this introduces a security vulnerability window, such roll-over
is not recommended.
6. Examples
6.1. Normal Operation
This section describes RIFT deployment in the example topology
without any node or link failures. We disregard flooding reduction
for simplicity's sake.
As first step, the following bi-directional adjacencies will be
created (and any other links that do not fulfill LIE rules in
Section 5.2.2 disregarded):
1. Spine 21 (PoD 0) to Spine 111, Spine 112, Spine 121, and Spine
122
2. Spine 22 (PoD 0) to Spine 111, Spine 112, Spine 121, and Spine
122
3. Spine 111 to Leaf 111, Leaf 112
4. Spine 112 to Leaf 111, Leaf 112
5. Spine 121 to Leaf 121, Leaf 122
6. Spine 122 to Leaf 121, Leaf 122
Consequently, N-TIEs would be originated by Spine 111 and Spine 112
and each set would be sent to both Spine 21 and Spine 22. N-TIEs
also would be originated by Leaf 111 (w/ Prefix 111) and Leaf 112 (w/
Prefix 112 and the multi-homed prefix) and each set would be sent to
Spine 111 and Spine 112. Spine 111 and Spine 112 would then flood
these N-TIEs to Spine 21 and Spine 22.
Similarly, N-TIEs would be originated by Spine 121 and Spine 122 and
each set would be sent to both Spine 21 and Spine 22. N-TIEs also
would be originated by Leaf 121 (w/ Prefix 121 and the multi-homed
prefix) and Leaf 122 (w/ Prefix 122) and each set would be sent to
Spine 121 and Spine 122. Spine 121 and Spine 122 would then flood
these N-TIEs to Spine 21 and Spine 22.
At this point both Spine 21 and Spine 22, as well as any controller
to which they are connected, would have the complete network
topology. At the same time, Spine 111/112/121/122 hold only the
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N-ties of level 0 of their respective PoD. Leafs hold only their own
N-TIEs.
S-TIEs with adjacencies and a default IP prefix would then be
originated by Spine 21 and Spine 22 and each would be flooded to
Spine 111, Spine 112, Spine 121, and Spine 122. Spine 111, Spine
112, Spine 121, and Spine 122 would each send the S-TIE from Spine 21
to Spine 22 and the S-TIE from Spine 22 to Spine 21. (S-TIEs are
reflected up to level from which they are received but they are NOT
propagated southbound.)
A S-TIE with a default IP prefix would be originated by Node 111 and
Spine 112 and each would be sent to Leaf 111 and Leaf 112.
Similarly, an S-TIE with a default IP prefix would be originated by
Node 121 and Spine 122 and each would be sent to Leaf 121 and Leaf
122. At this point IP connectivity with maximum possible ECMP has
been established between the leafs while constraining the amount of
information held by each node to the minimum necessary for normal
operation and dealing with failures.
6.2. Leaf Link Failure
. | | | |
.+-+---+-+ +-+---+-+
.| | | |
.|Spin111| |Spin112|
.+-+---+-+ ++----+-+
. | | | |
. | +---------------+ X
. | | | X Failure
. | +-------------+ | X
. | | | |
.+-+---+-+ +--+--+-+
.| | | |
.|Leaf111| |Leaf112|
.+-------+ +-------+
. + +
. Prefix111 Prefix112
Figure 32: Single Leaf link failure
In case of a failing leaf link between spine 112 and leaf 112 the
link-state information will cause re-computation of the necessary SPF
and the higher levels will stop forwarding towards prefix 112 through
spine 112. Only spines 111 and 112, as well as both spines will see
control traffic. Leaf 111 will receive a new S-TIE from spine 112
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and reflect back to spine 111. Spine 111 will de-aggregate prefix
111 and prefix 112 but we will not describe it further here since de-
aggregation is emphasized in the next example. It is worth observing
however in this example that if leaf 111 would keep on forwarding
traffic towards prefix 112 using the advertised south-bound default
of spine 112 the traffic would end up on Top-of-Fabric 21 and ToF 22
and cross back into pod 1 using spine 111. This is arguably not as
bad as black-holing present in the next example but clearly
undesirable. Fortunately, de-aggregation prevents this type of
behavior except for a transitory period of time.
6.3. Partitioned Fabric
. +--------+ +--------+ S-TIE of Spine21
. | | | | received by
. |ToF 21| |ToF 22| south reflection of
. ++-+--+-++ ++-+--+-++ spines 112 and 111
. | | | | | | | |
. | | | | | | | 0/0
. | | | | | | | |
. | | | | | | | |
. +--------------+ | +--- XXXXXX + | | | +---------------+
. | | | | | | | |
. | +-----------------------------+ | | |
. 0/0 | | | | | | |
. | 0/0 0/0 +- XXXXXXXXXXXXXXXXXXXXXXXXX -+ |
. | 1.1/16 | | | | | |
. | | +-+ +-0/0-----------+ | |
. | | | 1.1./16 | | | |
.+-+----++ +-+-----+ ++-----0/0 ++----0/0
.| | | | | 1.1/16 | 1.1/16
.|Spin111| |Spin112| |Spin121| |Spin122|
.+-+---+-+ ++----+-+ +-+---+-+ ++---+--+
. | | | | | | | |
. | +---------------+ | | +----------------+ |
. | | | | | | | |
. | +-------------+ | | | +--------------+ | |
. | | | | | | | |
.+-+---+-+ +--+--+-+ +-+---+-+ +---+-+-+
.| | | | | | | |
.|Leaf111| |Leaf112| |Leaf121| |Leaf122|
.+-+-----+ ++------+ +-----+-+ +-+-----+
. + + + +
. Prefix111 Prefix112 Prefix121 Prefix122
. 1.1/16
Figure 33: Fabric partition
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Figure 33 shows the arguably a more catastrophic but also a more
interesting case. Spine 21 is completely severed from access to
Prefix 121 (we use in the figure 1.1/16 as example) by double link
failure. However unlikely, if left unresolved, forwarding from leaf
111 and leaf 112 to prefix 121 would suffer 50% black-holing based on
pure default route advertisements by Top-of-Fabric 21 and ToF 22.
The mechanism used to resolve this scenario is hinging on the
distribution of southbound representation by Top-of-Fabric 21 that is
reflected by spine 111 and spine 112 to ToF 22. Spine 22, having
computed reachability to all prefixes in the network, advertises with
the default route the ones that are reachable only via lower level
neighbors that ToF 21 does not show an adjacency to. That results in
spine 111 and spine 112 obtaining a longest-prefix match to prefix
121 which leads through ToF 22 and prevents black-holing through ToF
21 still advertising the 0/0 aggregate only.
The prefix 121 advertised by Top-of-Fabric 22 does not have to be
propagated further towards leafs since they do no benefit from this
information. Hence the amount of flooding is restricted to ToF 21
reissuing its S-TIEs and south reflection of those by spine 111 and
spine 112. The resulting SPF in ToF 22 issues a new prefix S-TIEs
containing 1.1/16. None of the leafs become aware of the changes and
the failure is constrained strictly to the level that became
partitioned.
To finish with an example of the resulting sets computed using
notation introduced in Section 5.2.5, Top-of-Fabric 22 constructs the
following sets:
|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 Spine 21) = Spine 111, Spine 112
With that and |H (for r=prefix 121) and |H (for r=prefix 122) being
disjoint from |A (for Top-of-Fabric 21), ToF 22 will originate an
S-TIE with prefix 121 and prefix 122, that is flooded to spines 112,
112, 121 and 122.
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6.4. Northbound Partitioned Router and Optional East-West Links
. + + +
. X N1 | N2 | N3
. X | |
.+--+----+ +--+----+ +--+-----+
.| |0/0> <0/0| |0/0> <0/0| |
.| A01 +----------+ A02 +----------+ A03 | Level 1
.++-+-+--+ ++--+--++ +---+-+-++
. | | | | | | | | |
. | | +----------------------------------+ | | |
. | | | | | | | | |
. | +-------------+ | | | +--------------+ |
. | | | | | | | | |
. | +----------------+ | +-----------------+ |
. | | | | | | | | |
. | | +------------------------------------+ | |
. | | | | | | | | |
.++-+-+--+ | +---+---+ | +-+---+-++
.| | +-+ +-+ | |
.| L01 | | L02 | | L03 | Level 0
.+-------+ +-------+ +--------+
Figure 34: North Partitioned Router
Figure 34 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 5.2.4.1 A01 will compute northbound reachability by
using the link A01 to A02 (whereas A02 will NOT use this link during
N-SPF). Hence A01 will still advertise the default towards level 0
and route unidirectionally using the horizontal link.
As further consideration, the moment A02 looses link N2 the situation
evolves again. A01 will have no more northbound reachability while
still seeing A03 advertising northbound adjacencies in its south node
tie. With that it will stop advertising a default route due to
Section 5.2.3.8.
7. Implementation and Operation: Further Details
7.1. 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 leafs 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. Under normal conditions, the leaf needs to support a multipath
default route only. In most catastrophic partitioning case it
has to be capable of accommodating all the leaf routes in its own
PoD to prevent black-holing.
2. Leaf nodes hold only their own N-TIEs and S-TIEs of Level 1 nodes
they are connected to; so overall few in numbers.
3. Leaf node does not have to support any type of de-aggregation
computation or propagation.
4. Leaf nodes do not have to support overload bit normally.
5. Unless optional leaf-2-leaf procedures are desired default route
origination and S-TIE origination is unnecessary.
7.2. Considerations for Spine Implementation
In case of spines, i.e. nodes that will never act as Top of Fabric a
full implementation is not required, specifically the node does not
need to perform any computation of negative disaggregation except
respecting northbound disaggregation advertised from the north.
7.3. Adaptations to Other Proposed Data Center Topologies
. +-----+ +-----+
. | | | |
.+-+ S0 | | S1 |
.| ++---++ ++---++
.| | | | |
.| | +------------+ |
.| | | +------------+ |
.| | | | |
.| ++-+--+ +--+-++
.| | | | |
.| | A0 | | A1 |
.| +-+--++ ++---++
.| | | | |
.| | +------------+ |
.| | +-----------+ | |
.| | | | |
.| +-+-+-+ +--+-++
.+-+ | | |
. | L0 | | L1 |
. +-----+ +-----+
Figure 35: Level Shortcut
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Strictly speaking, RIFT is not limited to Clos variations only. The
protocol preconditions only a sense of 'compass rose direction'
achieved by configuration (or derivation) of levels and other
topologies are possible within this framework. So, conceptually, one
could include leaf to leaf links and even shortcut between levels but
certain requirements in Section 4 will not be met anymore. As an
example, shortcutting levels illustrated in Figure 35 will lead
either to suboptimal routing when L0 sends traffic to L1 (since using
S0's default route will lead to the traffic being sent back to A0 or
A1) or the leafs need each other's routes installed to understand
that only A0 and A1 should be used to talk to each other.
Whether such modifications of topology constraints make sense is
dependent on many technology variables and the exhausting treatment
of the topic is definitely outside the scope of this document.
7.4. Originating Non-Default Route Southbound
Obviously, an implementation may choose to originate southbound
instead of a strict default route (as described in Section 5.2.3.8) a
shorter prefix P' but in such a scenario all addresses carried within
the RIFT domain must be contained within P'.
8. Security Considerations
8.1. 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 vanishes. 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.
8.2. ZTP
Section 5.2.7 presents many attack vectors in untrusted environments,
starting with nodes that oscillate their level offers to the
possiblity of a node offering a three way adjacency with the highest
possible level value with a very long holdtime trying to put itself
"on top of the lattice" and with that gaining access to the whole
southbound topology. Session authentication mechanisms are necessary
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in environments where this is possible and RIFT provides the
according security envelope to ensure this if desired.
8.3. 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.
8.4. 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
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.
8.5. 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.
8.6. 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
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service attack seems unavoidable since the TIE origin key id is only
protected by the, here assumed to be compromised, node.
8.7. Host Implementations
It can be reasonably expected that with the proliferation of RotH
servers, rather than dedicated networking devices, will constitute
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 addressed within the protocol if the trust
model is breached, i.e. the server presents valid credentials to form
an adjacency and issue TIEs. However, in a move devious way, the
servers can present DoS (or even DDos) vectors of issuing too many
LIE packets, flood large amount of N-TIEs and similar anomalies. A
prudent implementation hosting leafs should implement thresholds and
raise warnings when leaf is advertising number of TIEs in excess of
those.
9. 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.
9.1. 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'.
9.2. Requested Registries with Suggested Values
This section requests registries that help govern the schema via
usual IANA registry procedures. Allocation of new values is always
performed via `Expert Review` action. IANA is requested to store the
schema version introducing the allocated value as well as,
optionally, its description when present. All values not suggested
as to be considered `Unassigned`. The range of every registry is a
16-bit integer.
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9.2.1. RIFT/common/AddressFamilyType
address family
9.2.1.1. Requested Entries
Name Value Schema Version Description
Illegal 0 2.0
AddressFamilyMinValue 1 2.0
IPv4 2 2.0
IPv6 3 2.0
AddressFamilyMaxValue 4 2.0
9.2.2. RIFT/common/HierarchyIndications
flags indicating nodes behavior in case of ZTP
9.2.2.1. Requested Entries
Name Value Schema Version Description
leaf_only 0 2.0
leaf_only_and_leaf_2_leaf_procedures 1 2.0
top_of_fabric 2 2.0
9.2.3. RIFT/common/IEEE802_1ASTimeStampType
timestamp per IEEE 802.1AS, values MUST be interpreted in
implementation as unsigned
9.2.3.1. Requested Entries
Name Value Schema Version Description
AS_sec 1 2.0
AS_nsec 2 2.0
9.2.4. RIFT/common/IPAddressType
IP address type
9.2.4.1. Requested Entries
Name Value Schema Version Description
ipv4address 1 2.0
ipv6address 2 2.0
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9.2.5. RIFT/common/IPPrefixType
prefix representing reachablity.
@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.
9.2.5.1. Requested Entries
Name Value Schema Version Description
ipv4prefix 1 2.0
ipv6prefix 2 2.0
9.2.6. RIFT/common/IPv4PrefixType
IP v4 prefix type
9.2.6.1. Requested Entries
Name Value Schema Version Description
address 1 2.0
prefixlen 2 2.0
9.2.7. RIFT/common/IPv6PrefixType
IP v6 prefix type
9.2.7.1. Requested Entries
Name Value Schema Version Description
address 1 2.0
prefixlen 2 2.0
9.2.8. RIFT/common/PrefixSequenceType
sequence of a prefix when it moves
9.2.8.1. Requested Entries
Name Value Schema Description
Version
timestamp 1 2.0
transactionid 2 2.0 transaction ID set by client in e.g.
in 6LoWPAN
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9.2.9. RIFT/common/RouteType
RIFT route types.
@note: route types which MUST be ordered on their preference PGP
prefixes are most preferred attracting traffic north (towards spine)
and then south normal prefixes are attracting traffic south (towards
leafs), i.e. prefix in NORTH PREFIX TIE is preferred over SOUTH
PREFIX TIE.
@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
9.2.9.1. Requested Entries
Name Value Schema Version Description
Illegal 0 2.0
RouteTypeMinValue 1 2.0
Discard 2 2.0
LocalPrefix 3 2.0
SouthPGPPrefix 4 2.0
NorthPGPPrefix 5 2.0
NorthPrefix 6 2.0
NorthExternalPrefix 7 2.0
SouthPrefix 8 2.0
SouthExternalPrefix 9 2.0
NegativeSouthPrefix 10 2.0
RouteTypeMaxValue 11 2.0
9.2.10. RIFT/common/TIETypeType
type of TIE.
This enum indicates what TIE type the TIE is carrying. In case the
value is not known to the receiver, re-flooded the same way as prefix
TIEs. This allows for future extensions of the protocol within the
same schema major with types opaque to some nodes unless the flooding
scope is not the same as prefix TIE, then a major version revision
MUST be performed.
9.2.10.1. Requested Entries
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Name Value Schema Description
Version
Illegal 0 2.0
TIETypeMinValue 1 2.0
NodeTIEType 2 2.0
PrefixTIEType 3 2.0
PositiveDisaggregationPrefixTIEType 4 2.0
NegativeDisaggregationPrefixTIEType 5 2.0
PGPrefixTIEType 6 2.0
KeyValueTIEType 7 2.0
ExternalPrefixTIEType 8 2.0
PositiveExternalDisaggregationPrefixTIEType 9 2.0
TIETypeMaxValue 10 2.0
9.2.11. RIFT/common/TieDirectionType
direction of tie
9.2.11.1. Requested Entries
Name Value Schema Version Description
Illegal 0 2.0
South 1 2.0
North 2 2.0
DirectionMaxValue 3 2.0
9.2.12. RIFT/encoding/Community
community
9.2.12.1. Requested Entries
Name Value Schema Version Description
top 1 2.0
bottom 2 2.0
9.2.13. RIFT/encoding/KeyValueTIEElement
Generic key value pairs
9.2.13.1. Requested Entries
Name Value Schema Description
Version
keyvalues 1 2.0 if the same key repeats in multiple TIEs of
same node or with different values, behavior
is unspecified
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9.2.14. RIFT/encoding/LIEPacket
RIFT LIE packet
@note this node's level is already included on the packet header
9.2.14.1. Requested Entries
Name Value Schema Description
Version
name 1 2.0 node or adjacency name
local_id 2 2.0 local link ID
flood_port 3 2.0 UDP port to which we can
receive flooded TIEs
link_mtu_size 4 2.0 layer 3 MTU, used to
discover to mismatch.
link_bandwidth 5 2.0 local link bandwidth on the
interface
neighbor 6 2.0 reflects the neighbor once
received to provide 3-way
connectivity
pod 7 2.0 node's PoD
node_capabilities 10 2.0 node capabilities shown in
the LIE. The capabilies
MUST match the capabilities
shown in the Node TIEs,
otherwise the behavior is
unspecified. A node
detecting the mismatch
SHOULD generate according
error
link_capabilities 11 2.0 capabilities of this link
holdtime 12 2.0 required holdtime of the
adjacency, i.e. how much
time MUST expire without
LIE for the adjacency to
drop
label 13 2.0 unsolicited, downstream
assigned locally
significant label value for
the adjacency
not_a_ztp_offer 21 2.0 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 2.0 indicates to northbound
neighbor that it should be
reflooding this node's
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N-TIEs to achieve flood
reduction and balancing for
northbound flooding. To be
ignored if received from a
northbound adjacency
you_are_sending_too_quickly 23 2.0 can be optionally set to
indicate to neighbor that
packet losses are seen on
reception based on packet
numbers or the rate is too
high. The receiver SHOULD
temporarily slow down
flooding rates
instance_name 24 2.0 instance name in case
multiple RIFT instances
running on same interface
9.2.15. RIFT/encoding/LinkCapabilities
link capabilities
9.2.15.1. Requested Entries
Name Value Schema Description
Version
bfd 1 2.0 indicates that the link is
supporting BFD
v4_forwarding_capable 2 2.0 indicates whether the interface
will support v4 forwarding. This
MUST be set to true when LIEs
from a v4 address are sent and
MAY be set to true in LIEs on v6
address. If v4 and v6 LIEs
indicate contradicting
information the behavior is
unspecified.
9.2.16. RIFT/encoding/LinkIDPair
LinkID pair describes one of parallel links between two nodes
9.2.16.1. Requested Entries
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Name Value Schema Description
Version
local_id 1 2.0 node-wide unique value for
the local link
remote_id 2 2.0 received remote link ID for
this link
platform_interface_index 10 2.0 describes the local
interface index of the link
platform_interface_name 11 2.0 describes the local
interface name
trusted_outer_security_key 12 2.0 indication 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 2.0 indication whether the link
is protected by established
BFD session
9.2.17. RIFT/encoding/Neighbor
neighbor structure
9.2.17.1. Requested Entries
Name Value Schema Version Description
originator 1 2.0 system ID of the originator
remote_id 2 2.0 ID of remote side of the link
9.2.18. RIFT/encoding/NodeCapabilities
capabilities the node supports. The schema may add to this field
future capabilities to indicate whether it will support
interpretation of future 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 is unavoidable.
9.2.18.1. Requested Entries
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Name Value Schema Description
Version
protocol_minor_version 1 2.0 must advertise supported minor
version dialect that way
flood_reduction 2 2.0 can this node participate in
flood reduction
hierarchy_indications 3 2.0 does this node restrict itself
to be top-of-fabric or leaf only
(in ZTP) and does it support
leaf-2-leaf procedures
9.2.19. RIFT/encoding/NodeFlags
Flags the node sets
9.2.19.1. Requested Entries
Name Value Schema Description
Version
overload 1 2.0 indicates that node is in overload, do not
transit traffic through it
9.2.20. RIFT/encoding/NodeNeighborsTIEElement
neighbor of a node
9.2.20.1. Requested Entries
Name Value Schema Description
Version
level 1 2.0 level of neighbor
cost 3 2.0
link_ids 4 2.0 can carry description of multiple parallel
links in a TIE
bandwidth 5 2.0 total bandwith to neighbor, this will be
normally sum of the bandwidths of all the
parallel links.
9.2.21. RIFT/encoding/NodeTIEElement
Description of a node.
It may occur multiple times in different TIEs but if either *
capabilities values do not match or * flags values do not match or *
neighbors repeat with different values
the behavior is undefined and a warning SHOULD be generated.
Neighbors can be distributed across multiple TIEs however if the sets
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are disjoint. Miscablings SHOULD be repeated in every node TIE,
otherwise the behavior is undefined.
@note: observe that absence of fields implies defined defaults
9.2.21.1. Requested Entries
Name Value Schema Description
Version
level 1 2.0 level of the node
neighbors 2 2.0 node's neighbors. If neighbor systemID
repeats in other node TIEs of same node
the behavior is undefined
capabilities 3 2.0 capabilities of the node
flags 4 2.0 flags of the node
name 5 2.0 optional node name for easier
operations
pod 6 2.0 PoD to which the node belongs
miscabled_links 10 2.0 if any local links are miscabled, the
indication is flooded
9.2.22. RIFT/encoding/PacketContent
content of a RIFT packet
9.2.22.1. Requested Entries
Name Value Schema Version Description
lie 1 2.0
tide 2 2.0
tire 3 2.0
tie 4 2.0
9.2.23. RIFT/encoding/PacketHeader
common RIFT packet header
9.2.23.1. Requested Entries
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Name Value Schema Description
Version
major_version 1 2.0 major version type of protocol
minor_version 2 2.0 minor version type of protocol
sender 3 2.0 node sending the packet, in case of
LIE/TIRE/TIDE also the originator of it
level 4 2.0 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.
9.2.24. RIFT/encoding/PrefixAttributes
9.2.24.1. Requested Entries
Name Value Schema Description
Version
metric 2 2.0 distance of the prefix
tags 3 2.0 generic unordered set of route tags,
can be redistributed to other
protocols or use within the context
of real time analytics
monotonic_clock 4 2.0 monotonic clock for mobile addresses
loopback 6 2.0 indicates if the interface is a node
loopback
directly_attached 7 2.0 indicates that the prefix is directly
attached, i.e. should be routed to
even if the node is in overload. *
from_link 10 2.0 in case of locally originated
prefixes, i.e. interface addresses
this can describe which link the
address belongs to.
9.2.25. RIFT/encoding/PrefixTIEElement
TIE carrying prefixes
9.2.25.1. Requested Entries
Name Value Schema Description
Version
prefixes 1 2.0 prefixes with the associated attributes. if
the same prefix repeats in multiple TIEs of
same node behavior is unspecified
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9.2.26. RIFT/encoding/ProtocolPacket
RIFT packet structure
9.2.26.1. Requested Entries
Name Value Schema Version Description
header 1 2.0
content 2 2.0
9.2.27. RIFT/encoding/TIDEPacket
TIDE with sorted TIE headers, if headers are unsorted, behavior is
undefined
9.2.27.1. Requested Entries
Name Value Schema Version Description
start_range 1 2.0 first TIE header in the tide packet
end_range 2 2.0 last TIE header in the tide packet
headers 3 2.0 _sorted_ list of headers
9.2.28. RIFT/encoding/TIEElement
single element in a TIE. 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 the TIE an error MUST be reported and the TIE MUST
be ignored.
This type can be extended with new optional elements for new
`common.TIETypeType` values without breaking the major but if it is
necessary to understand whether all nodes support the new type a node
capability must be added as well.
9.2.28.1. Requested Entries
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Name Valu Schema Description
e Versio
n
node 1 2.0 used in case of enum comm
on.TIETypeType.NodeTIETyp
e
prefixes 2 2.0 used in case of enum comm
on.TIETypeType.PrefixTIET
ype
positive_disaggregation_prefixe 3 2.0 positive prefixes (always
s southbound) It MUST NOT
be advertised within a
North TIE and ignored
otherwise
negative_disaggregation_prefixe 5 2.0 transitive, negative
s prefixes (always
southbound) which MUST be
aggregated and propagated
according to the
specification 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.
external_prefixes 6 2.0 externally reimported
prefixes
positive_external_disaggregatio 7 2.0 positive external
n_prefixes disaggregated prefixes
(always southbound). It
MUST NOT be advertised
within a North TIE and
ignored otherwise
keyvalues 9 2.0 Key-Value store elements
9.2.29. RIFT/encoding/TIEHeader
Header of a TIE.
@note: TIEID space is a total order achieved by comparing the
elements in sequence defined and comparing each value as an unsigned
integer of according length.
@note: After sequence number the lifetime received on the envelope
must be used for comparison before further fields.
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@note: `origination_time` and `origination_lifetime` are disregarded
for comparison purposes and carried purely for debugging/security
purposes if present.
9.2.29.1. Requested Entries
Name Value Schema Description
Version
tieid 2 2.0 ID of the tie
seq_nr 3 2.0 sequence number of the tie
origination_time 10 2.0 absolute timestamp when the TIE
was generated. This can be used on
fabrics with synchronized clock to
prevent lifetime modification
attacks.
origination_lifetime 12 2.0 original lifetime when the TIE was
generated. This can be used on
fabrics with synchronized clock to
prevent lifetime modification
attacks.
9.2.30. RIFT/encoding/TIEHeaderWithLifeTime
Header of a TIE as described in TIRE/TIDE.
9.2.30.1. Requested Entries
Name Value Schema Description
Version
header 1 2.0
remaining_lifetime 2 2.0 remaining lifetime that expires down
to 0 just like in ISIS. TIEs with
lifetimes differing by less than
`lifetime_diff2ignore` MUST be
considered EQUAL.
9.2.31. RIFT/encoding/TIEID
ID of a TIE
@note: TIEID space is a total order achieved by comparing the
elements in sequence defined and comparing each value as an unsigned
integer of according length.
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9.2.31.1. Requested Entries
Name Value Schema Version Description
direction 1 2.0 direction of TIE
originator 2 2.0 indicates originator of the TIE
tietype 3 2.0 type of the tie
tie_nr 4 2.0 number of the tie
9.2.32. RIFT/encoding/TIEPacket
TIE packet
9.2.32.1. Requested Entries
Name Value Schema Version Description
header 1 2.0
element 2 2.0
9.2.33. RIFT/encoding/TIREPacket
TIRE packet
9.2.33.1. Requested Entries
Name Value Schema Version Description
headers 1 2.0
10. 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 or implementation. 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
epistomology that allowed to tie current asynchronous distributed
systems theory results to a modern protocol design presented here.
Adrian Farrel, Joel Halpern, Jeffrey Zhang, Krzysztof Szarkowicz,
Nagendra Kumar 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 misconceptions about BFD's finer points. Artur
Makutunowicz pointed out many possible improvements and acted as
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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 leafs 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 while implementing.
11. References
11.1. Normative References
[ISO10589]
ISO "International Organization for Standardization",
"Intermediate system to Intermediate system intra-domain
routeing information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode Network Service (ISO 8473), ISO/IEC
10589:2002, Second Edition.", Nov 2002.
[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>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23,
RFC 2365, DOI 10.17487/RFC2365, July 1998,
<https://www.rfc-editor.org/info/rfc2365>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[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>.
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[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>.
[RFC5303] Katz, D., Saluja, R., and D. Eastlake 3rd, "Three-Way
Handshake for IS-IS Point-to-Point Adjacencies", RFC 5303,
DOI 10.17487/RFC5303, October 2008,
<https://www.rfc-editor.org/info/rfc5303>.
[RFC5549] Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network
Layer Reachability Information with an IPv6 Next Hop",
RFC 5549, DOI 10.17487/RFC5549, May 2009,
<https://www.rfc-editor.org/info/rfc5549>.
[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>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[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>.
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[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>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[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>.
11.2. Informative References
[CLOS] Yuan, X., "On Nonblocking Folded-Clos Networks in Computer
Communication Environments", IEEE International Parallel &
Distributed Processing Symposium, 2011.
[DIJKSTRA]
Dijkstra, E., "A Note on Two Problems in Connexion with
Graphs", Journal Numer. Math. , 1959.
[DOT] Ellson, J. and L. Koutsofios, "Graphviz: open source graph
drawing tools", Springer-Verlag , 2001.
[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.
[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>.
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[FATTREE] Leiserson, C., "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/>.
[ISO10589-Second-Edition]
International Organization for Standardization,
"Intermediate system to Intermediate system intra-domain
routeing information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode Network Service (ISO 8473)", Nov 2002.
[MAKSIC2013]
Maksic et al., N., "Improving Utilization of Data Center
Networks", IEEE Communications Magazine, Nov 2013.
[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>.
[RFC3626] Clausen, T., Ed. and P. Jacquet, Ed., "Optimized Link
State Routing Protocol (OLSR)", RFC 3626,
DOI 10.17487/RFC3626, October 2003,
<https://www.rfc-editor.org/info/rfc3626>.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
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[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>.
[RFC6518] Lebovitz, G. and M. Bhatia, "Keying and Authentication for
Routing Protocols (KARP) Design Guidelines", RFC 6518,
DOI 10.17487/RFC6518, February 2012,
<https://www.rfc-editor.org/info/rfc6518>.
[RFC7855] Previdi, S., Ed., Filsfils, C., Ed., Decraene, B.,
Litkowski, S., Horneffer, M., and R. Shakir, "Source
Packet Routing in Networking (SPRING) Problem Statement
and Requirements", RFC 7855, DOI 10.17487/RFC7855, May
2016, <https://www.rfc-editor.org/info/rfc7855>.
[RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of
BGP for Routing in Large-Scale Data Centers", RFC 7938,
DOI 10.17487/RFC7938, August 2016,
<https://www.rfc-editor.org/info/rfc7938>.
[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
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complement's substractions 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 >: relationsship is symmetric but not transitive. Observe that
this leaves the case of the numbers having maximum two complement
distance, e.g. ( 0 and 0x800 ) undefined in our 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:
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
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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 datatypes 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
10. changes any enumeration type except extending `common.TIEType`
(use of enumeration types is generally discouraged)
major version of the schema MUST increase. All other changes MUST
increase minor version within the same major.
Observe however that 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. common.thrift
/** @note MUST be interpreted in implementation as unsigned 64 bits.
* The implementation SHOULD NOT use the MSB.
*/
typedef i64 SystemIDType
typedef i32 IPv4Address
/** this has to be of length 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
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/** @note MUST be interpreted in implementation as unsigned */
typedef i32 MTUSizeType
/** @note MUST be interpreted in implementation as unsigned rollling over number */
typedef i16 SeqNrType
/** @note MUST be interpreted in implementation as unsigned */
typedef i32 LifeTimeInSecType
/** @note MUST be interpreted in implementation as unsigned */
typedef i8 LevelType
/** optional, recommended monotonically increasing number _per packet type per adjacency_
that can be used to detect losses/misordering/restarts.
This will be moved into envelope in the future.
@note MUST be interpreted in implementation as unsigned rollling over number */
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 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 */
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 string 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
typedef string KeyNameType
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, values MUST be interpreted in implementation as unsigned */
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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 nodes behavior 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 */
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
/** This MUST be used when node is configured as top of fabric in ZTP.
This is kept reasonably low to alow for fast ZTP convergence on
failures. */
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
/** 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 holddown time */
const TimeIntervalInSecType default_lie_holdtime = 3
/** 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
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/** by default e'one 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
/** round down interval when TIEs are sent with security hashes
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). This
constant MUST be larger than `purge_lifetime` to avoid
retransmissions */
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. If nonces are
changed every minute on both sides this opens statistically
a `maximum_valid_nonce_delta` minutes window of identical LIEs,
TIE, TI(x)E replays.
The interval cannot be too small since LIE FSM may change
states fairly quickly during ZTP without sending LIEs*/
const i16 maximum_valid_nonce_delta = 5;
/** direction of tie */
enum TieDirectionType {
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Illegal = 0,
South = 1,
North = 2,
DirectionMaxValue = 3,
}
/** address family */
enum AddressFamilyType {
Illegal = 0,
AddressFamilyMinValue = 1,
IPv4 = 2,
IPv6 = 3,
AddressFamilyMaxValue = 4,
}
/** IP v4 prefix type */
struct IPv4PrefixType {
1: required IPv4Address address;
2: required PrefixLenType prefixlen;
}
/** IP v6 prefix type */
struct IPv6PrefixType {
1: required IPv6Address address;
2: required PrefixLenType prefixlen;
}
/** IP address type */
union IPAddressType {
1: optional IPv4Address ipv4address;
2: optional IPv6Address ipv6address;
}
/** prefix representing reachablity.
@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;
}
/** sequence of a prefix when it moves
*/
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struct PrefixSequenceType {
1: required IEEE802_1ASTimeStampType timestamp;
/** transaction ID set by client in e.g. in 6LoWPAN */
2: optional PrefixTransactionIDType transactionid;
}
/** type of TIE.
This enum indicates what TIE type the TIE is carrying.
In case the value is not known to the receiver,
re-flooded the same way as prefix TIEs. This allows for
future extensions of the protocol within the same schema major
with types opaque to some nodes unless the flooding scope is not
the same as prefix TIE, then a major version revision MUST
be performed.
*/
enum TIETypeType {
Illegal = 0,
TIETypeMinValue = 1,
/** first legal value */
NodeTIEType = 2,
PrefixTIEType = 3,
PositiveDisaggregationPrefixTIEType = 4,
NegativeDisaggregationPrefixTIEType = 5,
PGPrefixTIEType = 6,
KeyValueTIEType = 7,
ExternalPrefixTIEType = 8,
PositiveExternalDisaggregationPrefixTIEType = 9,
TIETypeMaxValue = 10,
}
/** RIFT route types.
@note: route types which MUST be ordered on their preference
PGP prefixes are most preferred attracting
traffic north (towards spine) and then south
normal prefixes are attracting traffic south (towards leafs),
i.e. prefix in NORTH PREFIX TIE is preferred over SOUTH PREFIX TIE.
@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 prefered */
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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.2. encoding.thrift
/**
Thrift file for packet encodings for RIFT
*/
include "common.thrift"
/** Represents protocol encoding schema major version */
const common.VersionType protocol_major_version = 2
/** Represents protocol encoding schema minor version */
const common.MinorVersionType protocol_minor_version = 0
/** common RIFT packet header */
struct PacketHeader {
/** major version type of protocol */
1: required common.VersionType major_version = protocol_major_version;
/** minor version type of protocol */
2: required common.VersionType 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;
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/** 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;
}
/** community */
struct Community {
1: required i32 top;
2: required i32 bottom;
}
/** 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;
}
/** capabilities the node supports. The schema may add to this
field future capabilities to indicate whether it will support
interpretation of future 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 is unavoidable.
*/
struct NodeCapabilities {
/** must advertise supported minor version dialect that way */
1: required common.MinorVersionType protocol_minor_version =
protocol_minor_version;
/** can this node participate in flood reduction */
2: optional bool flood_reduction =
common.flood_reduction_default;
/** does this node restrict itself to be top-of-fabric or
leaf only (in ZTP) and does it support leaf-2-leaf procedures */
3: optional common.HierarchyIndications hierarchy_indications;
}
/** link capabilities */
struct LinkCapabilities {
/** indicates that the link is supporting BFD */
1: optional bool bfd =
common.bfd_default;
/** indicates whether the interface will support v4 forwarding. This MUST
* be set to true when LIEs from a v4 address are sent and MAY be set
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* to true in LIEs on v6 address. If v4 and v6 LIEs indicate contradicting
* information the behavior is unspecified. */
2: optional bool v4_forwarding_capable =
true;
}
/** 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 to 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;
/** node capabilities shown in the LIE. The capabilies
MUST match the capabilities shown in the Node TIEs, otherwise
the behavior is unspecified. A node detecting the mismatch
SHOULD generate according error */
10: required NodeCapabilities node_capabilities;
/** capabilities of this link */
11: optional LinkCapabilities link_capabilities;
/** required holdtime of the adjacency, i.e. how much time
MUST expire without LIE for the adjacency to drop */
12: required common.TimeIntervalInSecType holdtime =
common.default_lie_holdtime;
/** 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
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be reflooding this node's N-TIEs to achieve flood reduction and
balancing for northbound flooding. To be ignored if received from a
northbound adjacency */
22: optional bool you_are_flood_repeater =
common.default_you_are_flood_repeater;
/** can be optionally set to indicate to neighbor that packet losses are seen on
reception based on packet numbers or the rate is too high. The receiver SHOULD
temporarily slow down flooding rates
*/
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;
/** indication 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;
/** indication whether the link is protected by established BFD session */
13: optional bool bfd_up;
}
/** ID of a TIE
@note: TIEID space is a total order achieved by comparing the elements
in sequence defined and comparing each value as an
unsigned integer of according length.
*/
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;
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}
/** Header of a TIE.
@note: TIEID space is a total order achieved by comparing the elements
in sequence defined and comparing each value as an
unsigned integer of according length.
@note: After sequence number the lifetime received on the envelope
must be used for comparison before further fields.
@note: `origination_time` and `origination_lifetime` are disregarded
for comparison purposes and carried purely for debugging/security
purposes if present.
*/
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. This can be used on fabrics with
synchronized clock to prevent lifetime modification attacks. */
10: optional common.IEEE802_1ASTimeStampType origination_time;
/** original lifetime when the TIE
was generated. This can be used on fabrics with
synchronized clock to prevent lifetime modification attacks. */
12: optional common.LifeTimeInSecType origination_lifetime;
}
/** Header of a TIE as described in TIRE/TIDE.
*/
struct TIEHeaderWithLifeTime {
1: required TIEHeader header;
/** remaining lifetime that expires down to 0 just like in ISIS.
TIEs with lifetimes differing by less than `lifetime_diff2ignore` MUST
be considered EQUAL. */
2: required common.LifeTimeInSecType remaining_lifetime;
}
/** TIDE with sorted TIE headers, if headers are unsorted, behavior is undefined */
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 */
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3: required list<TIEHeaderWithLifeTime> headers;
}
/** TIRE packet */
struct TIREPacket {
1: required set<TIEHeaderWithLifeTime> headers;
}
/** neighbor of a node */
struct NodeNeighborsTIEElement {
/** level of neighbor */
1: required common.LevelType level;
/** Cost to neighbor.
@note: All parallel links to same node
incur same cost, in case the neighbor has multiple
parallel links at different cost, the largest distance
(highest numerical value) MUST be advertised
@note: any neighbor with cost <= 0 MUST be ignored in computations */
3: optional common.MetricType cost = common.default_distance;
/** can carry description of multiple parallel links in a TIE */
4: optional set<LinkIDPair> link_ids;
/** total bandwith to neighbor, this will be normally sum of the
bandwidths of all the parallel links. */
5: optional common.BandwithInMegaBitsType bandwidth =
common.default_bandwidth;
}
/** Flags the node sets */
struct NodeFlags {
/** indicates that node is in overload, do not transit traffic through it */
1: optional bool overload = common.overload_default;
}
/** Description of a node.
It may occur multiple times in different TIEs but if either
* capabilities values do not match or
* flags values do not match or
* neighbors repeat with different values
the behavior is undefined and a warning SHOULD be generated.
Neighbors can be distributed across multiple TIEs however if
the sets are disjoint. Miscablings SHOULD be repeated in every
node TIE, otherwise the behavior is undefined.
@note: observe that absence of fields implies defined defaults
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*/
struct NodeTIEElement {
/** level of the node */
1: required common.LevelType level;
/** node's neighbors. If neighbor systemID repeats in other node TIEs of
same node the behavior is undefined */
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;
/** if any local links are miscabled, the indication is flooded */
10: optional set<common.LinkIDType> miscabled_links;
}
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> tags;
/** monotonic clock for mobile addresses */
4: optional common.PrefixSequenceType monotonic_clock;
/** indicates if the interface is a node loopback */
6: optional bool loopback = false;
/** indicates that the prefix is directly attached, i.e. should be routed to even if
the node is in overload. **/
7: optional bool directly_attached = true;
/** in case of locally originated prefixes, i.e. interface addresses this can
describe which link the address belongs to. */
10: optional common.LinkIDType from_link;
}
/** TIE carrying prefixes */
struct PrefixTIEElement {
/** prefixes with the associated attributes.
if the same prefix repeats in multiple TIEs of same node
behavior is unspecified */
1: required map<common.IPPrefixType, PrefixAttributes> prefixes;
}
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/** Generic key value pairs */
struct KeyValueTIEElement {
/** if the same key repeats in multiple TIEs of same node
or with different values, behavior is unspecified */
1: required map<common.KeyIDType,string> keyvalues;
}
/** single element in a TIE. 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 the TIE an error MUST be reported and the TIE
MUST be ignored.
This type can be extended with new optional elements
for new `common.TIETypeType` values without breaking
the major but if it is necessary to understand whether
all nodes support the new type a node capability must
be added as well.
*/
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)
It MUST NOT be advertised within a North TIE and ignored otherwise
*/
3: optional PrefixTIEElement positive_disaggregation_prefixes;
/** transitive, negative prefixes (always southbound) which
MUST be aggregated and propagated
according to the specification
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.
*/
5: optional PrefixTIEElement negative_disaggregation_prefixes;
/** externally reimported prefixes */
6: optional PrefixTIEElement external_prefixes;
/** positive external disaggregated prefixes (always southbound).
It MUST NOT be advertised within a North TIE and ignored otherwise
*/
7: optional PrefixTIEElement positive_external_disaggregation_prefixes;
/** Key-Value store elements */
9: optional KeyValueTIEElement keyvalues;
}
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/** 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. Finite State Machines and Precise Operational
Specifications
Some FSM figures are provided as [DOT] description due to limitations
of ASCII art.
On Entry action is performed every time and right before the
according state is entered, i.e. after any transitions from previous
state.
On Exit action is 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.
The FSMs and procedures are NOT normative in the sense that an
implementation MUST implement them literally (which would be
overspecification) but an implementation MUST exhibit externally
observable behavior that is identical to the execution of the
specified FSMs.
Where a FSM representation is inconvenient, i.e. the amount of
procedures and kept state exceeds the amount of transitions, we defer
to a more procedural description on data structures.
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C.1. LIE FSM
Initial state is `OneWay`.
Event `MultipleNeighbors` 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
occurence of the event SHOULD generate a clear, according
notification to help operational deployments.
The machine sends LIEs on several transitions to accelerate adjacency
bring-up without waiting for the timer tic.
digraph Ga556dde74c30450aae125eaebc33bd57 {
Nd16ab5092c6b421c88da482eb4ae36b6[label="ThreeWay"][shape="oval"];
N54edd2b9de7641688608f44fca346303[label="OneWay"][shape="oval"];
Nfeef2e6859ae4567bd7613a32cc28c0e[label="TwoWay"][shape="oval"];
N7f2bb2e04270458cb5c9bb56c4b96e23[label="Enter"][style="invis"][shape="plain"];
N292744a4097f492f8605c926b924616b[label="Enter"][style="dashed"][shape="plain"];
Nc48847ba98e348efb45f5b78f4a5c987[label="Exit"][style="invis"][shape="plain"];
Nd16ab5092c6b421c88da482eb4ae36b6 -> N54edd2b9de7641688608f44fca346303
[label="|NeighborChangedLevel|\n|NeighborChangedAddress|\n|UnacceptableHeader|\n|MTUMismatch|\n|PODMismatch|\n|HoldtimeExpired|\n|MultipleNeighbors|"]
[color="black"][arrowhead="normal" dir="both" arrowtail="none"];
Nd16ab5092c6b421c88da482eb4ae36b6 -> Nd16ab5092c6b421c88da482eb4ae36b6
[label="|TimerTick|\n|LieRcvd|\n|SendLie|"][color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
Nfeef2e6859ae4567bd7613a32cc28c0e -> Nfeef2e6859ae4567bd7613a32cc28c0e
[label="|TimerTick|\n|LieRcvd|\n|SendLie|"][color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N54edd2b9de7641688608f44fca346303 -> Nd16ab5092c6b421c88da482eb4ae36b6
[label="|ValidReflection|"][color="red"][arrowhead="normal" dir="both" arrowtail="none"];
Nd16ab5092c6b421c88da482eb4ae36b6 -> Nd16ab5092c6b421c88da482eb4ae36b6
[label="|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"][color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Nd16ab5092c6b421c88da482eb4ae36b6 -> Nd16ab5092c6b421c88da482eb4ae36b6
[label="|ValidReflection|"][color="red"][arrowhead="normal" dir="both" arrowtail="none"];
Nfeef2e6859ae4567bd7613a32cc28c0e -> N54edd2b9de7641688608f44fca346303
[label="|LevelChanged|"][color="blue"][arrowhead="normal" dir="both" arrowtail="none"];
Nfeef2e6859ae4567bd7613a32cc28c0e -> N54edd2b9de7641688608f44fca346303
[label="|NeighborChangedLevel|\n|NeighborChangedAddress|\n|UnacceptableHeader|\n|MTUMismatch|\n|PODMismatch|\n|HoldtimeExpired|\n|MultipleNeighbors|"]
[color="black"][arrowhead="normal" dir="both" arrowtail="none"];
Nfeef2e6859ae4567bd7613a32cc28c0e -> Nd16ab5092c6b421c88da482eb4ae36b6
[label="|ValidReflection|"][color="red"][arrowhead="normal" dir="both" arrowtail="none"];
N54edd2b9de7641688608f44fca346303 -> N54edd2b9de7641688608f44fca346303
[label="|TimerTick|\n|LieRcvd|\n|NeighborChangedLevel|\n|NeighborChangedAddress|\n|UnacceptableHeader|\n|MTUMismatch|\n|PODMismatch|\n|HoldtimeExpired|\n|SendLie|"]
[color="black"][arrowhead="normal" dir="both" arrowtail="none"];
N292744a4097f492f8605c926b924616b -> N54edd2b9de7641688608f44fca346303
[label=""][color="black"][arrowhead="normal" dir="both" arrowtail="none"];
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Nd16ab5092c6b421c88da482eb4ae36b6 -> N54edd2b9de7641688608f44fca346303
[label="|LevelChanged|"][color="blue"][arrowhead="normal" dir="both" arrowtail="none"];
N54edd2b9de7641688608f44fca346303 -> Nfeef2e6859ae4567bd7613a32cc28c0e
[label="|NewNeighbor|"][color="black"][arrowhead="normal" dir="both" arrowtail="none"];
N54edd2b9de7641688608f44fca346303 -> N54edd2b9de7641688608f44fca346303
[label="|LevelChanged|\n|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"][arrowhead="normal" dir="both" arrowtail="none"];
Nfeef2e6859ae4567bd7613a32cc28c0e -> Nfeef2e6859ae4567bd7613a32cc28c0e
[label="|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"][arrowhead="normal" dir="both" arrowtail="none"];
Nd16ab5092c6b421c88da482eb4ae36b6 -> Nfeef2e6859ae4567bd7613a32cc28c0e
[label="|NeighborDroppedReflection|"]
[color="red"][arrowhead="normal" dir="both" arrowtail="none"];
N54edd2b9de7641688608f44fca346303 -> N54edd2b9de7641688608f44fca346303
[label="|NeighborDroppedReflection|"][color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
}
LIE FSM DOT
.. To be updated ..
LIE FSM Figure
Events
o TimerTick: one second timer tic
o LevelChanged: node's level has been changed by ZTP or
configuration
o HALChanged: best HAL computed by ZTP has changed
o HATChanged: HAT computed by ZTP has changed
o HALSChanged: set of HAL offering systems computed by ZTP has
changed
o LieRcvd: received LIE
o NewNeighbor: new neighbor parsed
o ValidReflection: received own reflection from neighbor
o NeighborDroppedReflection: lost previous own reflection from
neighbor
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o NeighborChangedLevel: neighbor changed advertised level
o NeighborChangedAddress: neighbor changed IP address
o UnacceptableHeader: unacceptable header seen
o MTUMismatch: MTU mismatched
o PODMismatch: Unacceptable PoD seen
o HoldtimeExpired: adjacency hold down expired
o MultipleNeighbors: more than one neighbor seen on interface
o SendLie: send a LIE out
o UpdateZTPOffer: update this node's ZTP offer
Actions
on TimerTick in TwoWay finishes in TwoWay: PUSH SendLie event, if
holdtime expired PUSH HoldtimeExpired event
on HALChanged in TwoWay finishes in TwoWay: store new HAL
on MTUMismatch in ThreeWay finishes in OneWay: no action
on HALChanged in ThreeWay finishes in ThreeWay: store new HAL
on ValidReflection in TwoWay finishes in ThreeWay: no action
on ValidReflection in OneWay finishes in ThreeWay: no action
on NeighborDroppedReflection in ThreeWay finishes in TwoWay: no
action
on LieRcvd in ThreeWay finishes in ThreeWay: PROCESS_LIE
on MultipleNeighbors in TwoWay finishes in OneWay: no action
on UnacceptableHeader in ThreeWay finishes in OneWay: no action
on MTUMismatch in TwoWay finishes in OneWay: no action
on LevelChanged in OneWay finishes in OneWay: update level with
event value, PUSH SendLie event
on UnacceptableHeader in TwoWay finishes in OneWay: no action
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on HALSChanged in TwoWay finishes in TwoWay: store HALS
on UpdateZTPOffer in TwoWay finishes in TwoWay: send offer to ZTP
FSM
on NeighborChangedLevel in TwoWay finishes in OneWay: no action
on NewNeighbor in OneWay finishes in TwoWay: PUSH SendLie event
on NeighborChangedAddress in ThreeWay finishes in OneWay: no
action
on HALChanged in OneWay finishes in OneWay: store new HAL
on NeighborChangedLevel in OneWay finishes in OneWay: no action
on HoldtimeExpired in TwoWay finishes in OneWay: no action
on SendLie in TwoWay finishes in TwoWay: SEND_LIE
on LevelChanged in TwoWay finishes in OneWay: update level with
event value
on NeighborChangedAddress in OneWay finishes in OneWay: no action
on HATChanged in TwoWay finishes in TwoWay: store HAT
on LieRcvd in TwoWay finishes in TwoWay: PROCESS_LIE
on MultipleNeighbors in ThreeWay finishes in OneWay: no action
on MTUMismatch in OneWay finishes in OneWay: no action
on SendLie in OneWay finishes in OneWay: SEND_LIE
on LieRcvd in OneWay finishes in OneWay: PROCESS_LIE
on TimerTick in ThreeWay finishes in ThreeWay: PUSH SendLie event,
if holdtime expired PUSH HoldtimeExpired event
on TimerTick in OneWay finishes in OneWay: PUSH SendLie event
on PODMismatch in ThreeWay finishes in OneWay: no action
on LevelChanged in ThreeWay finishes in OneWay: update level with
event value
on NeighborChangedLevel in ThreeWay finishes in OneWay: no action
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on UpdateZTPOffer in OneWay finishes in OneWay: send offer to ZTP
FSM
on UpdateZTPOffer in ThreeWay finishes in ThreeWay: send offer to
ZTP FSM
on HATChanged in OneWay finishes in OneWay: store HAT
on HATChanged in ThreeWay finishes in ThreeWay: store HAT
on HoldtimeExpired in OneWay finishes in OneWay: no action
on UnacceptableHeader in OneWay finishes in OneWay: no action
on PODMismatch in OneWay finishes in OneWay: no action
on SendLie in ThreeWay finishes in ThreeWay: SEND_LIE
on NeighborChangedAddress in TwoWay finishes in OneWay: no action
on ValidReflection in ThreeWay finishes in ThreeWay: no action
on HALSChanged in OneWay finishes in OneWay: store HALS
on HoldtimeExpired in ThreeWay finishes in OneWay: no action
on HALSChanged in ThreeWay finishes in ThreeWay: store HALS
on NeighborDroppedReflection in OneWay finishes in OneWay: no
action
on PODMismatch in TwoWay finishes in OneWay: no action
on Entry into OneWay: CLEANUP
Following words are used for well known procedures:
1. PUSH Event: pushes an event to be executed by the FSM upon exit
of this action
2. CLEANUP: neighbor MUST be reset to unknown
3. SEND_LIE: create 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
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3. setting `you_are_not_flood_repeater` to computed value
4. PROCESS_LIE:
1. if lie has wrong major version OR our own system ID or
invalid system ID then CLEANUP else
2. if lie has non matching MTUs then CLEANUP, PUSH
UpdateZTPOffer, PUSH MTUMismatch else
3. if PoD rules do not allow adjacency forming then CLEANUP,
PUSH PODMismatch, PUSH MTUMismatch else
4. if lie has undefined level OR my level is undefined OR this
node is leaf and remote level lower than HAT OR (lie's level
is not leaf AND its difference is more than one from my
level) then CLEANUP, PUSH UpdateZTPOffer, PUSH
UnacceptableHeader else
5. 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
4. if any of neighbor's flood address port, name, local
linkid changed then PUSH NeighborChangedMinorFields and
5. CHECK_THREE_WAY
5. CHECK_THREE_WAY: if current state is one-way do nothing else
1. if lie packet does not contain neighbor then if current state
is three-way then PUSH NeighborDroppedReflection else
2. if packet reflects this system's ID and local port and state
is three-way then PUSH event ValidReflection else PUSH event
MultipleNeighbors
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C.2. ZTP FSM
Initial state is ComputeBestOffer.
digraph Gd436cc3ced8c471eb30bd4f3ac946261 {
N06108ba9ac894d988b3e4e8ea5ace007
[label="Enter"]
[style="invis"]
[shape="plain"];
Na47ff5eac9aa4b2eaf12839af68aab1f
[label="MultipleNeighborsWait"]
[shape="oval"];
N57a829be68e2489d8dc6b84e10597d0b
[label="OneWay"]
[shape="oval"];
Na641d400819a468d987e31182cdb013e
[label="ThreeWay"]
[shape="oval"];
Necfbfc2d8e5b482682ee66e604450c7b
[label="Enter"]
[style="dashed"]
[shape="plain"];
N16db54bf2c5d48f093ad6c18e70081ee
[label="TwoWay"]
[shape="oval"];
N1b89016876b44cc1b9c1e4a735769560
[label="Exit"]
[style="invis"]
[shape="plain"];
N16db54bf2c5d48f093ad6c18e70081ee -> N57a829be68e2489d8dc6b84e10597d0b
[label="|NeighborChangedLevel|\n|NeighborChangedAddress|\n|UnacceptableHeader|\n|MTUMismatch|\n|PODMismatch|\n|HoldtimeExpired|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N57a829be68e2489d8dc6b84e10597d0b -> N57a829be68e2489d8dc6b84e10597d0b
[label="|NeighborDroppedReflection|"]
[color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
N57a829be68e2489d8dc6b84e10597d0b -> Na47ff5eac9aa4b2eaf12839af68aab1f
[label="|MultipleNeighbors|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
Necfbfc2d8e5b482682ee66e604450c7b -> N57a829be68e2489d8dc6b84e10597d0b
[label=""]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N57a829be68e2489d8dc6b84e10597d0b -> N16db54bf2c5d48f093ad6c18e70081ee
[label="|NewNeighbor|"]
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[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na641d400819a468d987e31182cdb013e -> Na47ff5eac9aa4b2eaf12839af68aab1f
[label="|MultipleNeighbors|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N16db54bf2c5d48f093ad6c18e70081ee -> N16db54bf2c5d48f093ad6c18e70081ee
[label="|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na641d400819a468d987e31182cdb013e -> N16db54bf2c5d48f093ad6c18e70081ee
[label="|NeighborDroppedReflection|"]
[color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na47ff5eac9aa4b2eaf12839af68aab1f -> Na47ff5eac9aa4b2eaf12839af68aab1f
[label="|TimerTick|\n|MultipleNeighbors|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N57a829be68e2489d8dc6b84e10597d0b -> N57a829be68e2489d8dc6b84e10597d0b
[label="|LevelChanged|\n|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na641d400819a468d987e31182cdb013e -> Na641d400819a468d987e31182cdb013e
[label="|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na641d400819a468d987e31182cdb013e -> N57a829be68e2489d8dc6b84e10597d0b
[label="|NeighborChangedLevel|\n|NeighborChangedAddress|\n|UnacceptableHeader|\n|MTUMismatch|\n|PODMismatch|\n|HoldtimeExpired|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na47ff5eac9aa4b2eaf12839af68aab1f -> Na47ff5eac9aa4b2eaf12839af68aab1f
[label="|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
N16db54bf2c5d48f093ad6c18e70081ee -> N57a829be68e2489d8dc6b84e10597d0b
[label="|LevelChanged|"]
[color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na641d400819a468d987e31182cdb013e -> N57a829be68e2489d8dc6b84e10597d0b
[label="|LevelChanged|"]
[color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
N16db54bf2c5d48f093ad6c18e70081ee -> Na47ff5eac9aa4b2eaf12839af68aab1f
[label="|MultipleNeighbors|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na47ff5eac9aa4b2eaf12839af68aab1f -> N57a829be68e2489d8dc6b84e10597d0b
[label="|MultipleNeighborsDone|"]
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[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N16db54bf2c5d48f093ad6c18e70081ee -> Na641d400819a468d987e31182cdb013e
[label="|ValidReflection|"]
[color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na47ff5eac9aa4b2eaf12839af68aab1f -> N57a829be68e2489d8dc6b84e10597d0b
[label="|LevelChanged|"]
[color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na641d400819a468d987e31182cdb013e -> Na641d400819a468d987e31182cdb013e
[label="|TimerTick|\n|LieRcvd|\n|SendLie|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N57a829be68e2489d8dc6b84e10597d0b -> N57a829be68e2489d8dc6b84e10597d0b
[label="|TimerTick|\n|LieRcvd|\n|NeighborChangedLevel|\n|NeighborChangedAddress|\n|NeighborAddressAdded|\n|UnacceptableHeader|\n|MTUMismatch|\n|PODMismatch|\n|HoldtimeExpired|\n|SendLie|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N57a829be68e2489d8dc6b84e10597d0b -> Na641d400819a468d987e31182cdb013e
[label="|ValidReflection|"]
[color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
N16db54bf2c5d48f093ad6c18e70081ee -> N16db54bf2c5d48f093ad6c18e70081ee
[label="|TimerTick|\n|LieRcvd|\n|SendLie|"]
[color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
Na641d400819a468d987e31182cdb013e -> Na641d400819a468d987e31182cdb013e
[label="|ValidReflection|"]
[color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
}
ZTP FSM DOT
Events
o TimerTick: one second timer tic
o LevelChanged: node's level has been changed by ZTP or
configuration
o HALChanged: best HAL computed by ZTP has changed
o HATChanged: HAT computed by ZTP has changed
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o HALSChanged: set of HAL offering systems computed by ZTP has
changed
o LieRcvd: received LIE
o NewNeighbor: new neighbor parsed
o ValidReflection: received own reflection from neighbor
o NeighborDroppedReflection: lost previous own reflection from
neighbor
o NeighborChangedLevel: neighbor changed advertised level
o NeighborChangedAddress: neighbor changed IP address
o UnacceptableHeader: unacceptable header seen
o MTUMismatch: MTU mismatched
o PODMismatch: Unacceptable PoD seen
o HoldtimeExpired: adjacency hold down expired
o MultipleNeighbors: more than one neighbor seen on interface
o MultipleNeighborsDone: cooldown for multiple neighbors expired
o SendLie: send a LIE out
o UpdateZTPOffer: update this node's ZTP offer
Actions
on MTUMismatch in OneWay finishes in OneWay: no action
on HoldtimeExpired in OneWay finishes in OneWay: no action
on LevelChanged in ThreeWay finishes in OneWay: update level with
event value
on MultipleNeighbors in MultipleNeighborsWait finishes in
MultipleNeighborsWait: start multiple neighbors timer as 4 *
DEFAULT_LIE_HOLDTIME
on HALChanged in MultipleNeighborsWait finishes in
MultipleNeighborsWait: store new HAL
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on NeighborChangedAddress in ThreeWay finishes in OneWay: no
action
on ValidReflection in OneWay finishes in ThreeWay: no action
on MTUMismatch in TwoWay finishes in OneWay: no action
on TimerTick in MultipleNeighborsWait finishes in
MultipleNeighborsWait: decrement MultipleNeighbors timer, if
expired PUSH MultipleNeighborsDone
on MultipleNeighborsDone in MultipleNeighborsWait finishes in
OneWay: decrement MultipleNeighbors timer, if expired PUSH
MultipleNeighborsDone
on HATChanged in ThreeWay finishes in ThreeWay: store HAT
on UpdateZTPOffer in TwoWay finishes in TwoWay: send offer to ZTP
FSM
on HALSChanged in TwoWay finishes in TwoWay: store HALS
on PODMismatch in TwoWay finishes in OneWay: no action
on LieRcvd in TwoWay finishes in TwoWay: PROCESS_LIE
on PODMismatch in ThreeWay finishes in OneWay: no action
on TimerTick in TwoWay finishes in TwoWay: PUSH SendLie event, if
holdtime expired PUSH HoldtimeExpired event
on SendLie in TwoWay finishes in TwoWay: SEND_LIE
on SendLie in OneWay finishes in OneWay: SEND_LIE
on TimerTick in OneWay finishes in OneWay: PUSH SendLie event
on HALChanged in OneWay finishes in OneWay: store new HAL
on HALSChanged in ThreeWay finishes in ThreeWay: store HALS
on NeighborChangedLevel in TwoWay finishes in OneWay: no action
on PODMismatch in OneWay finishes in OneWay: no action
on HoldtimeExpired in TwoWay finishes in OneWay: no action
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on TimerTick in ThreeWay finishes in ThreeWay: PUSH SendLie event,
if holdtime expired PUSH HoldtimeExpired event
on MultipleNeighbors in TwoWay finishes in MultipleNeighborsWait:
start multiple neighbors timer as 4 * DEFAULT_LIE_HOLDTIME
on UpdateZTPOffer in MultipleNeighborsWait finishes in
MultipleNeighborsWait: send offer to ZTP FSM
on LieRcvd in OneWay finishes in OneWay: PROCESS_LIE
on LevelChanged in MultipleNeighborsWait finishes in OneWay:
update level with event value
on UpdateZTPOffer in ThreeWay finishes in ThreeWay: send offer to
ZTP FSM
on HALChanged in TwoWay finishes in TwoWay: store new HAL
on UnacceptableHeader in OneWay finishes in OneWay: no action
on HALSChanged in OneWay finishes in OneWay: store HALS
on HALSChanged in MultipleNeighborsWait finishes in
MultipleNeighborsWait: store HALS
on SendLie in ThreeWay finishes in ThreeWay: SEND_LIE
on MTUMismatch in ThreeWay finishes in OneWay: no action
on HATChanged in MultipleNeighborsWait finishes in
MultipleNeighborsWait: store HAT
on NeighborChangedAddress in OneWay finishes in OneWay: no action
on ValidReflection in TwoWay finishes in ThreeWay: no action
on MultipleNeighbors in OneWay finishes in MultipleNeighborsWait:
start multiple neighbors timer as 4 * DEFAULT_LIE_HOLDTIME
on NeighborChangedLevel in OneWay finishes in OneWay: no action
on HATChanged in OneWay finishes in OneWay: store HAT
on NeighborDroppedReflection in OneWay finishes in OneWay: no
action
on HALChanged in ThreeWay finishes in ThreeWay: store new HAL
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on NeighborAddressAdded in OneWay finishes in OneWay: no action
on NeighborChangedAddress in TwoWay finishes in OneWay: no action
on LieRcvd in ThreeWay finishes in ThreeWay: PROCESS_LIE
on UnacceptableHeader in TwoWay finishes in OneWay: no action
on LevelChanged in TwoWay finishes in OneWay: update level with
event value
on HATChanged in TwoWay finishes in TwoWay: store HAT
on UpdateZTPOffer in OneWay finishes in OneWay: send offer to ZTP
FSM
on ValidReflection in ThreeWay finishes in ThreeWay: no action
on UnacceptableHeader in ThreeWay finishes in OneWay: no action
on HoldtimeExpired in ThreeWay finishes in OneWay: no action
on NeighborChangedLevel in ThreeWay finishes in OneWay: no action
on LevelChanged in OneWay finishes in OneWay: update level with
event value, PUSH SendLie event
on NewNeighbor in OneWay finishes in TwoWay: PUSH SendLie event
on NeighborDroppedReflection in ThreeWay finishes in TwoWay: no
action
on MultipleNeighbors in ThreeWay finishes in
MultipleNeighborsWait: start multiple neighbors timer as 4 *
DEFAULT_LIE_HOLDTIME
on Entry into OneWay: CLEANUP
Following words are used for well known procedures:
1. PUSH Event: pushes an event to be executed by the FSM upon exit
of this action
2. CLEANUP: neighbor MUST be reset to unknown
3. SEND_LIE: create a new LIE packet
1. reflecting the neighbor if known and valid and
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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
4. PROCESS_LIE:
1. if lie has wrong major version OR our own system ID or
invalid system ID then CLEANUP else
2. if lie has non matching MTUs then CLEANUP, PUSH
UpdateZTPOffer, PUSH MTUMismatch else
3. if PoD rules do not allow adjacency forming then CLEANUP,
PUSH PODMismatch, PUSH MTUMismatch else
4. if lie has undefined level OR my level is undefined OR this
node is leaf and remote level lower than HAT OR (lie's level
is not leaf AND its difference is more than one from my
level) then CLEANUP, PUSH UpdateZTPOffer, PUSH
UnacceptableHeader else
5. 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
4. if any of neighbor's flood address port, name, local
linkid changed then PUSH NeighborChangedMinorFields and
5. CHECK_THREE_WAY
5. CHECK_THREE_WAY: if current state is one-way do nothing else
1. if lie packet does not contain neighbor then if current state
is three-way then PUSH NeighborDroppedReflection else
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2. if packet reflects this system's ID and local port and state
is three-way then PUSH event ValidReflection else PUSH event
MultipleNeighbors
C.3. Flooding Procedures
Flooding Procedures are described in terms of a flooding state of an
adjacency and resulting operations on it driven by packet arrivals.
The FSM has basically a single state and is not well suited to
represent the behavior.
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). The encoded
packets provide hints to react accordingly to losses or overruns.
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 adequate features of the system such
as e.g. queue lengths or congestion indications in the protocol
packets.
C.3.1. FloodState Structure per Adjacency
The structure contains conceptually the following elements. The word
collection or queue indicates a set of elements that can be iterated:
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.
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 procedures operating on this
structure:
TIE Describes either a full RIFT TIE or accordingly just the
`TIEHeader` or `TIEID`. The according meaning is unambiguously
contained in the context of the algorithm.
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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 on TIES_ACK then
a. if TIE" 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.
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 following priorities if the
system cannot process all the collections in real time:
Elements on TIES_ACK should be processed with highest priority
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TIES_TX
TIES_REQ and TIES_RTX
C.3.2. TIDEs
`TIEID` and `TIEHeader` space forms a strict total order (modulo
uncomparable sequence numbers 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 implictly 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 of Floodstate
structure.
C.3.2.1. 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
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6. NEXT_TIDE_ID = END
The constant `TIRDEs_PER_PKT` SHOULD be generated 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.
C.3.2.2. TIDE Processing
On reception of TIDEs 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
CLEARKEYS: Collection of TIEIDs to be removed from flood state
queues
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
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i. if this is a N-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)
f. for all TIEs in CLEARKEYS remove_from_all_queues(TIE)
C.3.3. TIREs
C.3.3.1. TIRE Generation
There is not much to say here. 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 `lifetime` field
MUST be set to 0 to force reflooding from the neighbor even if the
TIEs seem to be same.
C.3.3.2. 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
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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)
C.3.4. TIEs Processing on Flood State Adjacency
On reception of TIEs the following processing is performed:
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
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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)
C.3.5. TIEs Processing When LSDB Received Newer Version on Other
Adjacencies
The Link State Database can be considered to be a switchboard that
does not need any flooding procedures but can be given new versions
of TIEs by a peer. Consecutively, a peer receives from the LSDB
newer versions of TIEs received by other peeers and processes them
(without any filtering) just like receving TIEs from its remote peer.
This publisher model can be implemented in many ways.
C.3.6. 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.
Appendix D. Constants
D.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 to |
| Multicast | Value, | 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 6: all_constants
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Authors' Addresses
Tony Przygienda (editor)
Juniper
1137 Innovation Way
Sunnyvale, CA
USA
Email: prz@juniper.net
Alankar Sharma
Comcast
1800 Bishops Gate Blvd
Mount Laurel, NJ 08054
US
Email: Alankar_Sharma@comcast.com
Pascal Thubert
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
MOUGINS - Sophia Antipolis 06254
FRANCE
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
Bruno Rijsman
Individual
Email: fl0w@yandex-team.ru
Dmitry Afanasiev
Yandex
Email: fl0w@yandex-team.ru
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