RIFT Working Group T. Przygienda, Ed.
Internet-Draft Juniper Networks
Intended status: Standards Track A. Sharma
Expires: December 23, 2018 Comcast
P. Thubert
Cisco
A. Atlas
Individual
J. Drake
Juniper Networks
Jun 21, 2018
RIFT: Routing in Fat Trees
draft-ietf-rift-rift-02
Abstract
This document outlines a specialized, dynamic routing protocol for
Clos and fat-tree network topologies. The protocol (1) deals with
automatic construction of fat-tree topologies based on detection of
links, (2) minimizes the amount of routing state held at each level,
(3) automatically prunes the topology distribution exchanges to 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 non-ECMP forwarding, (7) automatically re-
balances traffic towards the spines based on bandwidth available and
ultimately (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.
Status of This Memo
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This Internet-Draft will expire on December 23, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. Reference Frame . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Topology . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Requirement Considerations . . . . . . . . . . . . . . . . . 10
4. RIFT: Routing in Fat Trees . . . . . . . . . . . . . . . . . 12
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2. Specification . . . . . . . . . . . . . . . . . . . . . . 13
4.2.1. Transport . . . . . . . . . . . . . . . . . . . . . . 13
4.2.2. Link (Neighbor) Discovery (LIE Exchange) . . . . . . 13
4.2.3. Topology Exchange (TIE Exchange) . . . . . . . . . . 15
4.2.3.1. Topology Information Elements . . . . . . . . . . 15
4.2.3.2. South- and Northbound Representation . . . . . . 16
4.2.3.3. Flooding . . . . . . . . . . . . . . . . . . . . 19
4.2.3.4. TIE Flooding Scopes . . . . . . . . . . . . . . . 19
4.2.3.5. Initial and Periodic Database Synchronization . . 21
4.2.3.6. Purging . . . . . . . . . . . . . . . . . . . . . 21
4.2.3.7. Southbound Default Route Origination . . . . . . 22
4.2.3.8. Northbound TIE Flooding Reduction . . . . . . . . 22
4.2.4. Policy-Guided Prefixes . . . . . . . . . . . . . . . 26
4.2.4.1. Ingress Filtering . . . . . . . . . . . . . . . . 27
4.2.4.2. Applying Policy . . . . . . . . . . . . . . . . . 28
4.2.4.3. Store Policy-Guided Prefix for Route Computation
and Regeneration . . . . . . . . . . . . . . . . 29
4.2.4.4. Re-origination . . . . . . . . . . . . . . . . . 29
4.2.4.5. Overlap with Disaggregated Prefixes . . . . . . . 30
4.2.5. Reachability Computation . . . . . . . . . . . . . . 30
4.2.5.1. Northbound SPF . . . . . . . . . . . . . . . . . 30
4.2.5.2. Southbound SPF . . . . . . . . . . . . . . . . . 31
4.2.5.3. East-West Forwarding Within a Level . . . . . . . 31
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4.2.6. Attaching Prefixes . . . . . . . . . . . . . . . . . 32
4.2.7. Attaching Policy-Guided Prefixes . . . . . . . . . . 33
4.2.8. Automatic Disaggregation on Link & Node Failures . . 34
4.2.9. Optional Autoconfiguration . . . . . . . . . . . . . 37
4.2.9.1. Terminology . . . . . . . . . . . . . . . . . . . 38
4.2.9.2. Automatic SystemID Selection . . . . . . . . . . 39
4.2.9.3. Generic Fabric Example . . . . . . . . . . . . . 39
4.2.9.4. Level Determination Procedure . . . . . . . . . . 40
4.2.9.5. Resulting Topologies . . . . . . . . . . . . . . 41
4.2.10. Stability Considerations . . . . . . . . . . . . . . 43
4.3. Further Mechanisms . . . . . . . . . . . . . . . . . . . 44
4.3.1. Overload Bit . . . . . . . . . . . . . . . . . . . . 44
4.3.2. Optimized Route Computation on Leafs . . . . . . . . 44
4.3.3. Mobility . . . . . . . . . . . . . . . . . . . . . . 44
4.3.3.1. Clock Comparison . . . . . . . . . . . . . . . . 46
4.3.3.2. Interaction between Time Stamps and Sequence
Counters . . . . . . . . . . . . . . . . . . . . 46
4.3.3.3. Anycast vs. Unicast . . . . . . . . . . . . . . . 47
4.3.3.4. Overlays and Signaling . . . . . . . . . . . . . 47
4.3.4. Key/Value Store . . . . . . . . . . . . . . . . . . . 48
4.3.4.1. Southbound . . . . . . . . . . . . . . . . . . . 48
4.3.4.2. Northbound . . . . . . . . . . . . . . . . . . . 48
4.3.5. Interactions with BFD . . . . . . . . . . . . . . . . 48
4.3.6. Fabric Bandwidth Balancing . . . . . . . . . . . . . 49
4.3.6.1. Northbound Direction . . . . . . . . . . . . . . 49
4.3.6.2. Southbound Direction . . . . . . . . . . . . . . 51
4.3.7. Label Binding . . . . . . . . . . . . . . . . . . . . 52
4.3.8. Segment Routing Support with RIFT . . . . . . . . . . 52
4.3.8.1. Global Segment Identifiers Assignment . . . . . . 52
4.3.8.2. Distribution of Topology Information . . . . . . 52
4.3.9. Leaf to Leaf Procedures . . . . . . . . . . . . . . . 53
4.3.10. Other End-to-End Services . . . . . . . . . . . . . . 53
4.3.11. Address Family and Multi Topology Considerations . . 53
4.3.12. Reachability of Internal Nodes in the Fabric . . . . 54
4.3.13. One-Hop Healing of Levels with East-West Links . . . 54
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.1. Normal Operation . . . . . . . . . . . . . . . . . . . . 54
5.2. Leaf Link Failure . . . . . . . . . . . . . . . . . . . . 55
5.3. Partitioned Fabric . . . . . . . . . . . . . . . . . . . 56
5.4. Northbound Partitioned Router and Optional East-West
Links . . . . . . . . . . . . . . . . . . . . . . . . . . 58
6. Implementation and Operation: Further Details . . . . . . . . 59
6.1. Considerations for Leaf-Only Implementation . . . . . . . 60
6.2. Adaptations to Other Proposed Data Center Topologies . . 60
6.3. Originating Non-Default Route Southbound . . . . . . . . 61
7. Security Considerations . . . . . . . . . . . . . . . . . . . 61
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 62
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 62
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10. References . . . . . . . . . . . . . . . . . . . . . . . . . 62
10.1. Normative References . . . . . . . . . . . . . . . . . . 62
10.2. Informative References . . . . . . . . . . . . . . . . . 65
Appendix A. Information Elements Schema . . . . . . . . . . . . 66
A.1. common.thrift . . . . . . . . . . . . . . . . . . . . . . 67
A.2. encoding.thrift . . . . . . . . . . . . . . . . . . . . . 72
Appendix B. Finite State Machines . . . . . . . . . . . . . . . 77
B.1. LIE . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
B.2. ZTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Appendix C. Constants . . . . . . . . . . . . . . . . . . . . . 87
C.1. Configurable Protocol Constants . . . . . . . . . . . . . 87
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 87
1. Introduction
ANISOTROPIC
Clos [CLOS] and Fat-Tree [FATTREE] have gained prominence in today's
networking, primarily as result of the paradigm shift towards a
centralized data-center based architecture that is poised to deliver
a majority of computation and storage services in the future.
Today's routing protocols were geared towards a network with an
irregular topology and low degree of connectivity originally but
given they were the only available mechanisms, consequently several
attempts to apply those to Clos have been made. Most successfully
BGP [RFC4271] [RFC7938] has been extended to this purpose, not as
much due to its inherent suitability to solve the problem but rather
because the perceived capability to modify it "quicker" and the
immanent difficulties with link-state [DIJKSTRA] based protocols to
perform in large scale densely meshed topologies.
In looking at the problem through the lens of its 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 switch generates under normal conditions a default route
and floods it in the "southern" direction. Obviously, such
aggregation can blackhole in cases of misconfiguration or failures
and this has to be addressed somehow.
For the visually oriented reader, Figure 1 presents a first
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 routes to them. In the second row of the
database we indicate that a partial information of other nodes in the
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same level is available as well; the details of how this is achieved
should be postponed for the moment. Whereas when we look at the
"bottom" of the fabric we see that the topology of the leafs is
basically empty and they only hold a load balanced default route to
the next level.
The balance of this document details the resulting protocol and fills
in the missing details.
. [A,B,C,D]
. [E]
. +-----+ +-----+
. | E | | F | A/32 @ [C,D]
. +-+-+-+ +-+-+-+ B/32 @ [C,D]
. | | | | C/32 @ C
. | | +-----+ | D/32 @ D
. | | | |
. | +------+ |
. | | | |
. [A,B] +-+---+ | | +---+-+ [A,B]
. [D] | C +--+ +-+ D | [C]
. +-+-+-+ +-+-+-+
. 0/0 @ [E,F] | | | | 0/0 @ [E,F]
. A/32 @ A | | +-----+ | A/32 @ A
. B/32 @ B | | | | B/32 @ B
. | +------+ |
. | | | |
. +-+---+ | | +---+-+
. | A +--+ +-+ B |
. 0/0 @ [C,D] +-----+ +-----+ 0/0 @ [C,D]
Figure 1: RIFT information distribution
1.1. 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].
2. Reference Frame
2.1. 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
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shortest path first (SPF) [DIJKSTRA] computation and directed acyclic
graphs (DAG).
Level: Clos and Fat Tree networks are trees and 'level' denotes the
set of nodes at the same height in such a network, where the
bottom level is level 0. 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 for
Level 2, 1 and 0 respectively. Level 0 is often called leaf as
well.
Point of Delivery (PoD): A self-contained vertical slice of a Clos
or Fat Tree network containing normally only level 0 and level 1
nodes. It communicates with nodes in other PoDs via the spine.
We number PoDs to distinguish them and use PoD #0 to denote
"undefined" PoD.
Superspine: The set of nodes that provide inter-PoD communication
and have no northbound adjacencies. Superspine nodes do not
belong to any PoD and are assigned "undefined" PoD value to
indicate the equivalent of "any" PoD.
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 4.2.9).
Connected Spine: In case a spine level represents a connected graph
(discounting links terminating at different levels), we call it a
"connected spine", in case a spine level consists of multiple
partitions, we call it a "disconnected" or "partitioned spine".
In other terms, a spine without East-West links is disconnected
and is the typical configuration forf Clos and Fat Tree networks.
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.
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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.
Southbound representation: Information sent towards a lower level
representing only limited amount of information.
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. It can be thought of as
largely equivalent to ISIS LSPs or OSPF LSA. We will talk about
N-TIEs when talking about TIEs in the northbound representation
and S-TIEs for the southbound equivalent.
Node TIE: This is an acronym for a "Node Topology Information
Element", largely equivalent to OSPF Node LSA, i.e. it contains
all neighbors 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
and de-aggregated prefixes the node passes southbound.
Policy-Guided Information: Information that is passed in either
southbound direction or north-bound direction by the means of
diffusion and can be filtered via policies. Policy-Guided
Prefixes and KV Ties are examples of Policy-Guided Information.
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.
PGP: Policy-Guided Prefixes allow to support traffic engineering
that cannot be achieved by the means of SPF computation or normal
node and prefix S-TIE origination. S-PGPs are propagated in south
direction only and N-PGPs follow northern direction strictly.
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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.
FL: Flooding Leader for a specific system has a dedicated role to
flood TIEs of that system.
FR: Flooding Repeater for a specific system has a dedicated role to
flood TIEs of that system northbound. Similar to MPR in OSLR.
BAD: This is an acronym for Bandwidth Adjusted Distance. RIFT
calculates the amount of northbound bandwidth available towards a
node compared to other nodes at the same level and adjusts the
default route distance accordingly to allow for the lower level to
adjust their load balancing.
Overloaded: Applies to a node advertising `overload` attribute as
set. The semantics closely follow the meaning of the same
attribute in [ISO10589-Second-Edition].
2.2. Topology
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. +--------+ +--------+
. | | | | ^ N
. |Spine 21| |Spine 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 | | | | | |
.|Node111+----------+Node112| |Node121| |Node122|
.+-+---+-+ ++----+-+ +-+---+-+ ++---+--+
. | | | 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 two level spine-and-leaf topology
We will use this topology (called commonly a fat tree/network in
modern DC considerations [VAHDAT08] as homonym to the original
definition of the term [FATTREE]) in all further considerations. It
depicts a generic "fat-tree" and the concepts explained in three
levels here carry by induction for further levels and higher degrees
of connectivity. However, this document will deal with designs that
provide only sparser connectivity as well.
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3. 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
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 data
centers 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.
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
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control architectures like SPRING [RFC7855] or PCE
[RFC4655].
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.
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, idiomatic or policy-guided
information in stable state is highly desirable since it
leads to better stability and faster convergence behavior.
REQ13: Once a packet traverses a link in a "southbound" direction,
it must not take any further "northbound" steps along its
path to delivery to its destination under normal conditions.
Taking a path through the spine in cases where a shorter
path is available is highly undesirable.
REQ14: Parallel links between same set of nodes must be
distinguishable for SPF, failure and traffic engineering
purposes.
REQ15: The protocol must not rely on interfaces having discernible
unique addresses, i.e. it must operate in presence of
unnumbered links (even parallel ones) or links of a single
node having 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 AP within a sub-second period.
Following list represents possible requirements and requirements
under discussion:
PEND1: Supporting anything but point-to-point links is a non-
requirement. Questions remain: for connecting to the
leaves, is there a case where multipoint is desirable? One
could still model it as point-to-point links; it seems there
is no need for anything more than a NBMA-type construct.
PEND2: What is the maximum scale of number leaf prefixes we need to
carry. Is 500'000 enough ?
Finally, following are the non-requirements:
NONREQ1: Broadcast media support is unnecessary.
NONREQ2: Purging 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.
4. 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 path-
vector [RFC4271] protocol when "pointing south". Albeit an unusual
combination, it does quite naturally exhibit the desirable properties
we seek.
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4.1. Overview
The singular property of RIFT is that it floods only northbound
"flat" link-state information so that each level understands the full
topology of levels south of it. That information is never flooded
East-West or back South again. In the southbound direction the
protocol operates like a "unidirectional" path vector protocol or
rather a distance vector with implicit split horizon whereas the
information only propagates one hop south and is 're-advertised' by
nodes at next lower level. However, we use flooding in the southern
direction as well to avoid the necessity to build an update per
neighbor. We leave the East-West direction out for the moment.
Those information flow constraints create a "smooth" information
propagation where nodes do not receive the same information from
multiple fronts which would force them to perform a diffused
computation to tie-break the same reachability information arriving
on arbitrary links and ultimately force hop-by-hop forwarding on
shortest-paths only.
To account for the "northern" and the "southern" information split
the link state database is partitioned into "north representation"
and "south representation" TIEs, whereas in simplest terms the N-TIEs
contain a link state topology description of lower levels and and
S-TIEs carry simply default routes. This oversimplified view will be
refined gradually in following sections while introducing protocol
procedures aimed to fulfill the described requirements.
4.2. Specification
4.2.1. Transport
All protocol elements are carried over UDP. Once QUIC [QUIC]
achieves the desired stability in deployments it may prove a valuable
candidate for TIE transport.
All packet formats are defined in Thrift models in Appendix A.
Future versions may include a [PROTOBUF] schema.
4.2.2. Link (Neighbor) Discovery (LIE Exchange)
LIE exchange happens over well-known administratively locally scoped
and configured or otherwise well-known IPv4 multicast address
[RFC2365] or link-local multicast scope [RFC4291] for IPv6 [RFC8200]
using a configured or otherwise a well-known destination UDP port
defined in Appendix C.1. LIEs SHOULD be sent with a TTL of 1 to
prevent RIFT information reaching beyond a single L3 next-hop in the
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topology. LIEs SHOULD be sent with network control precendence.
Originating port of the LIE has no further significance. LIEs are
exchanged over all links running RIFT. An implementation MAY listen
and send LIEs on IPv4 and/or IPv6 multicast addresses. 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 transmission should occur over the same
interface the LIEs have been received on. A node can use any of the
neighbor's LIE source addresses to send TIEs.
Unless Section 4.2.9 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
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.
A node tries to form a three way adjacency if and only if
(definitions of LEAF_ONLY are found in Section 4.2.9)
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 nodes with level higher than the neighboring node
OR
ii) the node is not at level 0 and the neighboring node is at
level 0 OR
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iii) both nodes are at level 0 AND both indicate support for
Section 4.3.9 OR
iii) neither node is at level 0 and the neighboring node is at
most one level away
].
Rule in Paragraph 3 MAY be optionally disregarded by a node if PoD
detection is undesirable or has to be disregarded.
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 [RFC5303]. Precise
finite state machines will be provided in later versions of this
specification. LIE packets contain nonces and may contain an SHA-1
[RFC6234] over nonces and some of the LIE data which prevents
corruption and replay attacks. TIE flooding reuses those nonces to
prevent mismatches and can use those for security purposes in case it
is using QUIC [QUIC]. Section 7 will address the precise security
mechanisms in the future.
4.2.3. Topology Exchange (TIE Exchange)
4.2.3.1. Topology Information Elements
Topology and reachability information in RIFT is conveyed by the
means of TIEs which have good amount of commonalities with LSAs in
OSPF.
TIE exchange mechanism uses 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.
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TIEs contain sequence numbers, lifetimes and a type. Each type has a
large 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
point of the design space is a prefix per TIE which leads to BGP-like
behavior vs. dense packing into few TIEs leading to more traditional
IGP trade-off with fewer TIEs. An implementation may even rehash 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 A.
4.2.3.2. South- and Northbound Representation
As a central concept to RIFT, each node represents itself differently
depending on the direction in which it is advertising information.
More precisely, a spine node represents two different databases to
its neighbors 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, local prefixes and
northbound policy-guided prefixes while the S-TIEs hold only all of
the node's adjacencies, the default prefix with necessary
disaggregated prefixes, local prefixes and southbound policy-guided
prefixes. We will explain this in detail further in Section 4.2.8
and Section 4.2.4.
The TIE types are symmetric in both directions and Table 1 provides a
quick reference to the different TIE types including direction and
their function.
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+----------+--------------------------------------------------------+
| TIE-Type | Content |
+----------+--------------------------------------------------------+
| node | node properties, adjacencies and information helping |
| N-TIE | in complex disaggregation scenarios |
+----------+--------------------------------------------------------+
| node | same content as node N-TIE except the information to |
| S-TIE | help disaggregation |
+----------+--------------------------------------------------------+
| Prefix | contains nodes' directly reachable prefixes |
| N-TIE | |
+----------+--------------------------------------------------------+
| Prefix | contains originated defaults and de-aggregated |
| S-TIE | prefixes |
+----------+--------------------------------------------------------+
| PGP | contains nodes north PGPs |
| N-TIE | |
+----------+--------------------------------------------------------+
| PGP | contains nodes south PGPs |
| S-TIE | |
+----------+--------------------------------------------------------+
| KV | contains nodes northbound KVs |
| N-TIE | |
+----------+--------------------------------------------------------+
| KV | contains nodes southbound KVs |
| S-TIE | |
+----------+--------------------------------------------------------+
Table 1: TIE Types
As an example illustrating a databases holding both representations,
consider the topology in Figure 2 with the optional link between node
111 and node 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 and the PGP 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((Node111, level 1, cost 1),
(Node112, level 1, cost 1), (Node121, level 1, cost 1),
(Node122, level 1, cost 1)))
Prefix S-TIE:
SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1))
Node111 S-TIEs:
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Node S-TIE:
NodeElement(level=1, neighbors((Spine21, level 2, cost 1, links(...)),
(Spine22, level 2, cost 1, links(...)),
(Node112, 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))
Node111 N-TIEs:
Node N-TIE:
NodeElement(level=1,
neighbors((Spine21, level 2, cost 1, links(...)),
(Spine22, level 2, cost 1, links(...)),
(Node112, level 1, cost 1, links(...)),
(Leaf111, level 0, cost 1, links(...)),
(Leaf112, level 0, cost 1, links(...))))
Prefix N-TIE:
NorthPrefixesElement(prefixes(Node111.loopback)
Node121 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))
Node121 N-TIEs:
Node N-TIE:
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(Node121.loopback)
Leaf112 N-TIEs:
Node N-TIE:
NodeElement(level=0,
neighbors((Node111, level 1, cost 1, links(...)),
(Node112, level 1, cost 1, links(...))))
Prefix N-TIE:
NorthPrefixesElement(prefixes(Leaf112.loopback, Prefix112,
Prefix_MH))
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Figure 3: example TIES generated in a 2 level spine-and-leaf topology
4.2.3.3. 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
flloding is initially more demanding to implement it avoids many
problems with update style used in diffused computation such as path
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 4.2.3.8.
As described before, TIEs themselves are transported over UDP with
the ports indicated in the LIE exchanges and using the destination
address (for unnumbered IPv4 interfaces same considerations apply as
in equivalent OSPF case) on which the LIE adjacency has been formed.
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 will be provided in
later versions of this specification.
4.2.3.4. TIE Flooding Scopes
In a somewhat analogous fashion to link-local, area and domain
flooding scopes, RIFT defines several complex "flooding scopes"
depending on the direction and type of TIE propagated.
Every 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 a 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
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level from which it was received. It should be noted that East-West
links are included in South TIE flooding; those TIEs need to be
flooded to satisfy algorithms in Section 4.2.5. 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 2. Those rules govern as well what SHOULD be included in TIDEs
towards neighbors. East-West flooding scopes are identical to South
flooding scopes.
Node S-TIE "reflection" allows to support disaggregation on failures
describes in Section 4.2.8 and flooding reduction in Section 4.2.3.8.
+--------------+----------------------------+-----------------------+
| Packet Type | South | North |
| vs. Peer | | |
| Direction | | |
+--------------+----------------------------+-----------------------+
| node S-TIE | flood self-originated only | flood if TIE |
| | | originator's level is |
| | | higher than own level |
+--------------+----------------------------+-----------------------+
| non-node | flood self-originated only | flood only if TIE |
| S-TIE | | originator is equal |
| | | peer |
+--------------+----------------------------+-----------------------+
| all N-TIEs | never flood | flood always |
+--------------+----------------------------+-----------------------+
| TIDE | include TIEs in flooding | include TIEs in |
| | scope | flooding scope |
+--------------+----------------------------+-----------------------+
| TIRE | include all N-TIEs and all | include only if TIE |
| | peer's self-originated | originator is equal |
| | TIEs and all node S-TIEs | peer |
+--------------+----------------------------+-----------------------+
Table 2: Flooding Scopes
As an example to illustrate these rules, consider using the topology
in Figure 2, with the optional link between node 111 and node 112,
and the associated TIEs given in Figure 3. The flooding from
particular nodes of the TIEs is given in Table 3.
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+------------+----------+-------------------------------------------+
| Router | Neighbor | TIEs |
| floods to | | |
+------------+----------+-------------------------------------------+
| Leaf111 | Node112 | Leaf111 N-TIEs, Node111 node S-TIE |
| Leaf111 | Node111 | Leaf111 N-TIEs, Node112 node S-TIE |
| | | |
| Node111 | Leaf111 | Node111 S-TIEs |
| Node111 | Leaf112 | Node111 S-TIEs |
| Node111 | Node112 | Node111 S-TIEs |
| Node111 | Spine21 | Node111 N-TIEs, Leaf111 N-TIEs, Leaf112 |
| | | N-TIEs, Spine22 node S-TIE |
| Node111 | Spine22 | Node111 N-TIEs, Leaf111 N-TIEs, Leaf112 |
| | | N-TIEs, Spine21 node S-TIE |
| | | |
| ... | ... | ... |
| Spine21 | Node111 | Spine21 S-TIEs |
| Spine21 | Node112 | Spine21 S-TIEs |
| Spine21 | Node121 | Spine21 S-TIEs |
| Spine21 | Node122 | Spine21 S-TIEs |
| ... | ... | ... |
+------------+----------+-------------------------------------------+
Table 3: Flooding some TIEs from example topology
4.2.3.5. 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 2.
4.2.3.6. Purging
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.
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Each node will 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 supercede 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.
4.2.3.7. Southbound Default Route Origination
Under certain conditions nodes issue a default route in their South
Prefix TIEs with metrics as computed in Section 4.3.6.1.
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.
4.2.3.8. 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:
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1. a node MUST flood self-originated N-TIE 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
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.
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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. An optional
boolean information `you_are_not_flood_repeater` in a LIE packet to a
parent is set to indicate that the parent is not an FR and that it
SHOULD NOT reflood N-TIEs.
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.
The algorithm consists of the following steps:
1. derive a 16-bits pseudo-random unsigned integer PR(N) from N's
system ID by splitting it in 16-bits-long words W1, W2, ..., Wn
and then XOR'ing the circularly shifted resulting words together,
and casting the resulting representation:
1. (unsigned integer) (W1<<1 xor (W2<<2) xor ... xor (Wn<<n) );
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2. sort the parents by decreasing number of northbound adjacencies:
sort |P(N) by decreasing CN(P), for all P in |P(N), as ordered
array |A(N);
3. 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 k=k+1;
2. set j=i;
3. while 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;
/* 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) */
/* At this point k is the total number of subarrays, initialized
for the shuffling operation below */
4. shuffle individually each subarrays |A_k(N) of cardinality C_k(N)
within |A(N) using a Fisher-Yates method 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];
2. set k=k-1;
5. for each grandparent, initialize a counter with the number of its
Southbound adjacencies :
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1. for each G in |G(N) set c(G) = CS(G);
6. 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. else
1. for all adjacencies ADJ(P, G) in |NA(P)
1. decrement c(G);
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.
4.2.4. Policy-Guided Prefixes
In a fat tree, it can be sometimes desirable to guide traffic to
particular destinations or keep specific flows to certain paths. In
RIFT, this is done by using policy-guided prefixes with their
associated communities. Each community is an abstract value whose
meaning is determined by configuration. It is assumed that the
fabric is under a single administrative control so that the meaning
and intent of the communities is understood by all the nodes in the
fabric. Any node can originate a policy-guided prefix.
Since RIFT uses distance vector concepts in a southbound direction,
it is straightforward to add a policy-guided prefix to an S-TIE. For
easier troubleshooting, the approach taken in RIFT is that a node's
southbound policy-guided prefixes are sent in its S-TIE and the
receiver does inbound filtering based on the associated communities
(an egress policy is imaginable but would lead to different S-TIEs
per neighbor possibly which is not considered in RIFT protocol
procedures). A southbound policy-guided prefix can only use links in
the south direction. If an PGP S-TIE is received on an East-West or
northbound link, it must be discarded by ingress filtering.
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Conceptually, a southbound policy-guided prefix guides traffic from
the leaves up to at most the north-most level. It is also necessary
to to have northbound policy-guided prefixes to guide traffic from
the north-most level down to the appropriate leaves. Therefore, RIFT
includes northbound policy-guided prefixes in its N PGP-TIE and the
receiver does inbound filtering based on the associated communities.
A northbound policy-guided prefix can only use links in the northern
direction. If an N PGP TIE is received on an East-West or southbound
link, it must be discarded by ingress filtering.
By separating southbound and northbound policy-guided prefixes and
requiring that the cost associated with a PGP is strictly
monotonically increasing at each hop, the path cannot loop. Because
the costs are strictly increasing, it is not possible to have a loop
between a northbound PGP and a southbound PGP. If East-West links
were to be allowed, then looping could occur and issues such as
counting to infinity would become an issue to be solved. If complete
generality of path - such as including East-West links and using both
north and south links in arbitrary sequence - then a Path Vector
protocol or a similar solution must be considered.
If a node has received the same prefix, after ingress filtering, as a
PGP in an S-TIE and in an N-TIE, then the node determines which
policy-guided prefix to use based upon the advertised cost.
A policy-guided prefix is always preferred to a regular prefix, even
if the policy-guided prefix has a larger cost. Appendix A provides
normative indication of prefix preferences.
The set of policy-guided prefixes received in a TIE is subject to
ingress filtering and then re-originated to be sent out in the
receiver's appropriate TIE. Both the ingress filtering and the re-
origination use the communities associated with the policy-guided
prefixes to determine the correct behavior. The cost on re-
advertisement MUST increase in a strictly monotonic fashion.
4.2.4.1. Ingress Filtering
When a node X receives a PGP S-TIE or a PGP N-TIE that is originated
from a node Y which does not have an adjacency with X, all PGPs in
such a TIE MUST be filtered. Similarly, if node Y is at the same
level as node X, then X MUST filter out PGPs in such S- and N-TIEs to
prevent loops.
Next, policy can be applied to determine which policy-guided prefixes
to accept. Since ingress filtering is chosen rather than egress
filtering and per-neighbor PGPs, policy that applies to links is done
at the receiver. Because the RIFT adjacency is between nodes and
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there may be parallel links between the two nodes, the policy-guided
prefix is considered to start with the next-hop set that has all
links to the originating node Y.
A policy-guided prefix has or is assigned the following attributes:
cost: This is initialized to the cost received
community_list: This is initialized to the list of the communities
received.
next_hop_set: This is initialized to the set of links to the
originating node Y.
4.2.4.2. Applying Policy
The specific action to apply based upon a community is deployment
specific. Here are some examples of things that can be done with
communities. The length of a community is a 64 bits number and it
can be written as a single field M or as a multi-field (S = M[0-31],
T = M[32-63]) in these examples. For simplicity, the policy-guided
prefix is referred to as P, the processing node as X and the
originator as Y.
Prune Next-Hops: Community Required: For each next-hop in
P.next_hop_set, if the next-hop does not have the community, prune
that next-hop from P.next_hop_set.
Prune Next-Hops: Avoid Community: For each next-hop in
P.next_hop_set, if the next-hop has the community, prune that
next-hop from P.next_hop_set.
Drop if Community: If node X has community M, discard P.
Drop if not Community: If node X does not have the community M,
discard P.
Prune to ifIndex T: For each next-hop in P.next_hop_set, if the
next-hop's ifIndex is not the value T specified in the community
(S,T), then prune that next-hop from P.next_hop_set.
Add Cost T: For each appearance of community S in P.community_list,
if the node X has community S, then add T to P.cost.
Accumulate Min-BW T: Let bw be the sum of the bandwidth for
P.next_hop_set. If that sum is less than T, then replace (S,T)
with (S, bw).
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Add Community T if Node matches S: If the node X has community S,
then add community T to P.community_list.
4.2.4.3. Store Policy-Guided Prefix for Route Computation and
Regeneration
Once a policy-guided prefix has completed ingress filtering and
policy, it is almost ready to store and use. It is still necessary
to adjust the cost of the prefix to account for the link from the
computing node X to the originating neighbor node Y.
There are three different policies that can be used:
Minimum Equal-Cost: Find the loWest cost C next-hops in
P.next_hop_set and prune to those. Add C to P.cost.
Minimum Unequal-Cost: Find the loWest cost C next-hop in
P.next_hop_set. Add C to P.cost.
Maximum Unequal-Cost: Find the highest cost C next-hop in
P.next_hop_set. Add C to P.cost.
The default policy is Minimum Unequal-Cost but well-known communities
can be defined to get the other behaviors.
Regardless of the policy used, a node MUST store a PGP cost that is
at least 1 greater than the PGP cost received. This enforces the
strictly monotonically increasing condition that avoids loops.
Two databases of PGPs - from N-TIEs and from S-TIEs are stored. When
a PGP is inserted into the appropriate database, the usual tie-
breaking on cost is performed. Observe that the node retains all PGP
TIEs due to normal flooding behavior and hence loss of the best
prefix will lead to re-evaluation of TIEs present and re-
advertisement of a new best PGP.
4.2.4.4. Re-origination
A node must re-originate policy-guided prefixes and retransmit them.
The node has its database of southbound policy-guided prefixes to
send in its S-TIE and its database of northbound policy-guided
prefixes to send in its N-TIE.
Of course, a leaf does not need to re-originate southbound policy-
guided prefixes.
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4.2.4.5. Overlap with Disaggregated Prefixes
PGPs may overlap with prefixes introduced by automatic de-
aggregation. The topic is under further discussion. The break in
connectivity that leads to infeasibility of a PGP is mirrored in
adjacency tear-down and according removal of such PGPs.
Nevertheless, the underlying link-state flooding will be likely
reacting significantly faster than a hop-by-hop redistribution and
with that the preference for PGPs may cause intermittent black-holes.
4.2.5. 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. A node can also have a set of PGPs.
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" (with due considerations given
to PGPs), it is possible to compute non-equal-cost or even k-shortest
paths [EPPSTEIN] and "saturate" the fabric to the extent desired.
4.2.5.1. 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.
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.
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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
2. the node does not originate a non-default supersuming prefix
itself.
i.e. the E-W link can be used as the 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 5.4.
4.2.5.2. 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.
4.2.5.3. East-West Forwarding Within a Level
Ultimately, it should be observed that in presence of a "ring" of E-W
links in a 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.
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4.2.6. Attaching Prefixes
After the SPF is run, it is necessary to attach according 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, type=spf, path_distance, next-hop
set), accumulates these results. Obviously, the prefix retains its
type which is used to tie-break between the same prefix advertised
with different types.
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 cost next-hop to that neighbor. Then
each prefix can be added into the RIFT route database with the
next_hop_set; ties are broken based upon type first and then
distance. RIFT route preferences are normalized by the according
thrift model type.
An exemplary implementation for node X follows:
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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, type=DistVector, P.cost, next_hop_set) to route_database
end if
if (P in route_database) and
(route_database[P].type is not PolicyGuided):
if route_database[P].cost > P.cost):
update route_database[P] with (P, DistVector, P.cost, next_hop_set)
else if route_database[P].cost == P.cost
update route_database[P] with (P, DistVector, P.cost,
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 4: Adding Routes from S-TIE Prefixes
4.2.7. Attaching Policy-Guided Prefixes
Each policy-guided prefix P has its cost and next_hop_set already
stored in the associated database, as specified in Section 4.2.4.3;
the cost stored for the PGP is already updated to considering the
cost of the link to the advertising neighbor. By definition, a
policy-guided prefix is preferred to a regular prefix.
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for each policy-guided prefix P:
if P not in route_database:
add (P, type=PolicyGuided, P.cost, next_hop_set)
end if
if P in route_database :
if (route_database[P].type is not PolicyGuided) or
(route_database[P].cost > P.cost):
update route_database[P] with (P, PolicyGuided, P.cost, next_hop_set)
else if route_database[P].cost == P.cost
update route_database[P] with (P, PolicyGuided, P.cost,
merge(next_hop_set, route_database[P].next_hop_set))
else
// Not preferred route so ignore
end if
end if
end for
Figure 5: Adding Routes from Policy-Guided Prefixes
4.2.8. Automatic Disaggregation on Link & Node Failures
Under normal circumstances, node's S-TIEs contain just the
adjacencies, a default route and policy-guided prefixes. 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 as 'de-
aggregation' or 'dis-aggregation'.
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. 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
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be |H(r). Observe that policy-guided prefixes are NOT affected
since their distribution scope is controlled by configuration.
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.
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. 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 or East-West neighbor. If it can,
then prefix disaggregation may be required. If it can't, then no
prefix disaggregation is needed. An example of disaggregation is
provided in Section 5.3.
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.
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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 its SPF based upon the received N-TIEs. 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.
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 6: Computation to Disaggregate Prefixes
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Each disaggregated prefix is sent with the accurate 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 4.3.1 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
complicate things unnecessarily. The PoD containing the prefix
will prefer southbound anyway.
4. 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 only.
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.
Ultimately, complex partitions of superspine on sparsely connected
fabrics can lead to necessity of transitive disaggregation through
multiple levels. The topic will be described and standardized in
later versions of this document.
4.2.9. Optional Autoconfiguration
Each RIFT node can optionally operate in zero touch provisioning
(ZTP) mode, i.e. it has no configuration (unless it is a superspine
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. This section describes the necessary
concepts and procedures.
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4.2.9.1. Terminology
Automatic Level Derivation: Procedures which allow nodes without
level configured to derive it automatically. Only applied if
CONFIGURED_LEVEL is undefined.
UNDEFINED_LEVEL: An imaginary 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".
SUPERSPINE_FLAG and CONFIGURED_LEVEL cannot be defined at the same
time as this flag. It implies CONFIGURED_LEVEL value of 0.
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. SUPERSPINE_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 4.3.9.
SUPERSPINE_FLAG is ignored when set at the same time as this flag.
LEAF_2_LEAF implies LEAF_ONLY and the according restrictions.
LEVEL_VALUE: In ZTP case the original definition of "level" in
Section 2.1 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). Offers
from LIEs with `not_a_ztp_offer` being true are not VOLs either.
Highest Available Level (HAL): Highest defined level value seen from
all VOLs received.
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Highest Adjacency Three Way (HAT): Highest neigbhor level of all the
formed three way adjacencies for the node.
SUPERSPINE_FLAG: Configuration flag provided to all superspines.
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
superspine nodes which is unavoidable since an initial 'seed' is
needed for other ZTP nodes to derive their level in the topology.
4.2.9.2. Automatic SystemID Selection
RIFT identifies each node via a SystemID which is a 64 bits wide
integer. It is relatively simple to derive a, for all practical
purposes collision free, value for each node on startup. For that
purpose, a node MUST use as system ID EUI-64 MA-L format where the
organizationally governed 24 bits can be used to generate system IDs
for multiple RIFT instances running on the system.
The router MUST ensure that such identifier is not changing very
frequently (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 suggested in Section 7 are
implemented).
4.2.9.3. 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 7. We assume all
nodes being in the same PoD.
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. +---+
. | A | s = SUPERSPINE_FLAG
. | s | l = LEAF_ONLY
. ++-++ l2l = LEAF_2_LEAF
. | |
. +--+ +--+
. | |
. +--++ ++--+
. | E | | F |
. | +-+ | +-----------+
. ++--+ | ++-++ |
. | | | | |
. | +-------+ | |
. | | | | |
. | | +----+ | |
. | | | | |
. ++-++ ++-++ |
. | I +-----+ J | |
. | | | +-+ |
. ++-++ +--++ | |
. | | | | |
. +---------+ | +------+ |
. | | | | |
. +-----------------+ | |
. | | | | |
. ++-++ ++-++ |
. | X +-----+ Y +-+
. |l2l| | l |
. +---+ +---+
Figure 7: Generic ZTP Cabling Considerations
First, we must anchor the "top" of the cabling and that's what the
SUPERSPINE_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
will see further then whether Y chooses to form adjacencies to F or
I, J successively.
4.2.9.4. Level Determination Procedure
A node starting up with UNDEFINED_VALUE (i.e. without a
CONFIGURED_LEVEL or any leaf or superspine flag) MUST follow those
additional procedures:
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1. It advertises its LEVEL_VALUE on all LIEs (observe that this can
be UNDEFINED_LEVEL which in terms of the schema is simply an
omitted optional value).
2. It chooses on an ongoing basis from all VOLs the value of
MAX(HAL-1,0) as its DERIVED_LEVEL. The node then starts to
advertise this derived level.
3. 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.
4. A node MUST reset any adjacency that has changed the level it is
offering and is in three way state.
5. 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.
6. After a level has been derived the node MUST set the
`not_a_ztp_offer` on LIEs towards all systems extending a VOL for
HAL.
A node starting with LEVEL_VALUE being 0 (i.e. it assumes a leaf
function by being configured with the appropriate flags or has a
CONFIGURED_LEVEL of 0) MUST follow those additional procedures:
1. It computes HAT per procedures above but does NOT use it to
compute DERIVED_LEVEL. HAT is used to limit adjacency formation
per Section 4.2.2.
Precise finite state machines will be provided in later versions of
this specification.
4.2.9.5. Resulting Topologies
The procedures defined in Section 4.2.9.4 will lead to the RIFT
topology and levels depicted in Figure 8.
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. +---+
. | As|
. | 24|
. ++-++
. | |
. +--+ +--+
. | |
. +--++ ++--+
. | E | | F |
. | 23+-+ | 23+-----------+
. ++--+ | ++-++ |
. | | | | |
. | +-------+ | |
. | | | | |
. | | +----+ | |
. | | | | |
. ++-++ ++-++ |
. | I +-----+ J | |
. | 22| | 22| |
. ++--+ +--++ |
. | | |
. +---------+ | |
. | | |
. ++-++ +---+ |
. | X | | Y +-+
. | 0 | | 0 |
. +---+ +---+
Figure 8: Generic ZTP Topology Autoconfigured
In case we imagine the LEAF_ONLY restriction on Y is removed the
outcome would be very different however and result in Figure 9. This
demonstrates basically that auto configuration prevents miscabling
detection and with that can lead to undesirable effects in cases
where leafs are not "nailed" by the accordingly configured flags and
arbitrarily cabled.
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. +---+
. | As|
. | 24|
. ++-++
. | |
. +--+ +--+
. | |
. +--++ ++--+
. | E | | F |
. | 23+-+ | 23+-------+
. ++--+ | ++-++ |
. | | | | |
. | +-------+ | |
. | | | | |
. | | +----+ | |
. | | | | |
. ++-++ ++-++ +-+-+
. | I +-----+ J +-----+ Y |
. | 22| | 22| | 22|
. ++-++ +--++ ++-++
. | | | | |
. | +-----------------+ |
. | | |
. +---------+ | |
. | | |
. ++-++ |
. | X +--------+
. | 0 |
. +---+
Figure 9: Generic ZTP Topology Autoconfigured
4.2.10. 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.
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4.3. Further Mechanisms
4.3.1. Overload Bit
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.
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.
4.3.2. Optimized Route Computation on Leafs
Since the leafs do see only "one hop away" they do not need to run a
full SPF but can simply gather prefix candidates from their neighbors
and build the according routing table.
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 interfaces, determining bi-directionality from the associated
N-TIE, and specifying the neighbor's next_hop_set set and cost from
the minimum cost local interfaces to that neighbor.
Then a leaf attaches prefixes as in Section 4.2.6 as well as the
policy-guided prefixes as in Section 4.2.7.
4.3.3. 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 memorizes 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
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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][RFC3315].
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 MUST advertise a time stamp of the latest sighting
of a prefix, e.g., by snooping IP protocols or the switch using
the 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" [I-D.ietf-6lo-rfc6775-update], 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.
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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.
4.3.3.1. 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 [I-D.ietf-6lo-rfc6775-update].
4.3.3.2. 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
that the counters stay comparable within the resolution of the time
stampling mechanism.
The sequence counter in [I-D.ietf-6lo-rfc6775-update] is encoded as
one octet, wraps after 127 increments, and, by default, values are
defined as comparable as long as they are less than SEQUENCE_WINDOW =
16 apart. An implementation MAY allow this to be configurable
throughout the domain, and the number can be pushed up to 64 and
still preserve the capability to discover an error situation where
counters are not comparable.
Within the resolution of MAXIMUM_CLOCK_DELTA the sequence counters
captured during 2 sequential values of the time stamp must be
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comparable. This means with default values that a node may move up
to 16 times during a 200 milliseconds period and the clocks remain
still comparable thus allowing the infrastructure to assert the
freshest advertisement with no ambiguity.
4.3.3.3. 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 4.3.3.1.
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
[I-D.ietf-6lo-rfc6775-update] movements on the fabric within
intervals smaller than 100msec will be seen as anycast.
4.3.3.4. Overlays and Signaling
RIFT is agnostic whichever the overlay technology [MIP, LISP, VxLAN,
NVO3] and the associated signaling is deployed over it. But it is
expected that leaf nodes, and possibly superspine nodes can perform
the according 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
tunneling from leaf to the superspines may be desired. Future
versions of this document may describe support for such tunneling in
RIFT.
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4.3.4. Key/Value Store
4.3.4.1. 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 a node to which the receiver has an
adjacency are considered.
2. Within all 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 originator 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 but
a diffused computation.
4.3.4.2. 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.
4.3.5. 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.
In case established BFD session goes Down after it was Up, RIFT
adjacency should be re-initialized started from Init.
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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 both the hello 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].
4.3.6. 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 approximative way based on the fact that RIFT is loop-
free.
4.3.6.1. 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 | |
. +-+---+-+ +-+---+-+
. | | | |
. |Node111| |Node112|
. +-+---+++ ++----+++
. |x || || ||
. || |+---------------+ ||
. || +---------------+| ||
. || || || ||
. || || || ||
. -----All Links 10 MBit-------
. || || || ||
. || || || ||
. || +------------+| || ||
. || |+------------+ || ||
. |x || || ||
. +-+---+++ +--++-+++
. | | | |
. |Leaf111| |Leaf112|
. +-------+ +-------+
Figure 10: Balancing Bandwidth
All links from Leafs in Figure 10 are assumed to 10 MBit/s bandwidth
while the uplinks one level further up are assumed to be 100 MBit/s.
Further, in Figure 10 we assume that Leaf111 lost one of the parallel
links to Node 111 and with that wants to possibly push more traffic
onto Node 112. Leaf 112 has equal bandwidth to Node 111 and Node 112
but Node 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 | Node111 | 110 | 7 | 2 |
+---------+---------+-------+-------+-----+
| Leaf111 | Node112 | 220 | 8 | 1 |
+---------+---------+-------+-------+-----+
| Leaf112 | Node111 | 120 | 7 | 2 |
+---------+---------+-------+-------+-----+
| Leaf112 | Node112 | 220 | 8 | 1 |
+---------+---------+-------+-------+-----+
Table 4: BAD Computation
All the multiplications and additions are saturating, i.e. when
exceeding range of the bandwidth type are set to highest possible
value of the type.
Observe that since BAD is only computed for default routes any
disaggregated prefixes so PGP or disaggregated routes are not
affected, however, a node MAY choose to compute and use BAD for other
routes.
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.
4.3.6.2. Southbound Direction
Due to its loop free properties a node could 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"
nodes based as what it sees is the total achievable maximum flow
through those nodes. It is worth observing that such computations
will work better if standardized but does not have to be necessarily.
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As long the packet keeps on heading south it will take one of the
available paths and arrive at the intended destination.
Future versions of this document will fill in more details.
4.3.7. 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.
4.3.8. Segment Routing Support with RIFT
Recently, alternative architecture to reuse labels as segment
identifiers [I-D.ietf-spring-segment-routing] has gained traction and
may present use cases in DC 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.
4.3.8.1. 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 superspine 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.
4.3.8.2. 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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4.3.9. 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).
4.3.10. Other End-to-End Services
Losing full, flat topology information at every node will have an
impact on some of the end-to-end network services. This is the price
paid for minimal disturbance in case of failures and reduced flooding
and memory requirements on nodes lower south in the level hierarchy.
4.3.11. Address Family and Multi Topology Considerations
Multi-Topology (MT)[RFC5120] and Multi-Instance (MI)[RFC6822] 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 4.3.5 are implementation dependent when
multiple RIFT instances run on the same link.
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4.3.12. 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 Prefix TIEs.
Things get more interesting in case a node looses all its northbound
adjacencies but is not at the top of the fabric. In such a case a
node that detects that some other members at its level are
advertising northbound adjacencies MAY inject its loopback address
into southbound PGP TIE and become reachable "from the south" that
way. Further, a solution may be implemented where based on e.g. a
"well known" community such a southbound PGP is reflected at level 0
and advertised as northbound PGP again to allow for "reachability
from the north" at the cost of additional flooding.
4.3.13. One-Hop Healing of Levels with East-West Links
Based on the rules defined in Section 4.2.5, Section 4.2.3.7 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. Section 5.4 explains the resulting behavior
based on one such example.
5. Examples
5.1. 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 4.2.2 disregarded):
1. Spine 21 (PoD 0) to Node 111, Node 112, Node 121, and Node 122
2. Spine 22 (PoD 0) to Node 111, Node 112, Node 121, and Node 122
3. Node 111 to Leaf 111, Leaf 112
4. Node 112 to Leaf 111, Leaf 112
5. Node 121 to Leaf 121, Leaf 122
6. Node 122 to Leaf 121, Leaf 122
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Consequently, N-TIEs would be originated by Node 111 and Node 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
Node 111 and Node 112. Node 111 and Node 112 would then flood these
N-TIEs to Spine 21 and Spine 22.
Similarly, N-TIEs would be originated by Node 121 and Node 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
Node 121 and Node 122. Node 121 and Node 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, Node 111/112/121/122 hold only the
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 Node
111, Node 112, Node 121, and Node 122. Node 111, Node 112, Node 121,
and Node 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.)
An S Tie with a default IP prefix would be originated by Node 111 and
Node 112 and each would be sent to Leaf 111 and Leaf 112. Leaf 111
and Leaf 112 would each send the S-TIE from Node 111 to Node 112 and
the S-TIE from Node 112 to Node 111.
Similarly, an S Tie with a default IP prefix would be originated by
Node 121 and Node 122 and each would be sent to Leaf 121 and Leaf
122. Leaf 121 and Leaf 122 would each send the S-TIE from Node 121
to Node 122 and the S-TIE from Node 122 to Node 121. 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.
5.2. Leaf Link Failure
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. | | | |
.+-+---+-+ +-+---+-+
.| | | |
.|Node111| |Node112|
.+-+---+-+ ++----+-+
. | | | |
. | +---------------+ X
. | | | X Failure
. | +-------------+ | X
. | | | |
.+-+---+-+ +--+--+-+
.| | | |
.|Leaf111| |Leaf112|
.+-------+ +-------+
. + +
. Prefix111 Prefix112
Figure 11: Single Leaf link failure
In case of a failing leaf link between node 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
node 112. Only nodes 111 and 112, as well as both spines will see
control traffic. Leaf 111 will receive a new S-TIE from node 112 and
reflect back to node 111. Node 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 node 112 the traffic would end up on spine 21 and spine 22 and
cross back into pod 1 using node 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.
5.3. Partitioned Fabric
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. +--------+ +--------+ S-TIE of Spine21
. | | | | received by
. |Spine 21| |Spine 22| reflection of
. ++-+--+-++ ++-+--+-++ Nodes 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
.|Node111| |Node112| |Node121| |Node122|
.+-+---+-+ ++----+-+ +-+---+-+ ++---+--+
. | | | | | | | |
. | +---------------+ | | +----------------+ |
. | | | | | | | |
. | +-------------+ | | | +--------------+ | |
. | | | | | | | |
.+-+---+-+ +--+--+-+ +-+---+-+ +---+-+-+
.| | | | | | | |
.|Leaf111| |Leaf112| |Leaf121| |Leaf122|
.+-+-----+ ++------+ +-----+-+ +-+-----+
. + + + +
. Prefix111 Prefix112 Prefix121 Prefix122
. 1.1/16
Figure 12: Fabric partition
Figure 12 shows the arguably most catastrophic but also the most
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 spine 21 and spine 22.
The mechanism used to resolve this scenario is hinging on the
distribution of southbound representation by spine 21 that is
reflected by node 111 and node 112 to spine 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
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neighbors that spine 21 does not show an adjacency to. That results
in node 111 and node 112 obtaining a longest-prefix match to prefix
121 which leads through spine 22 and prevents black-holing through
spine 21 still advertising the 0/0 aggregate only.
The prefix 121 advertised by spine 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 spine 21 reissuing its
S-TIEs and reflection of those by node 111 and node 112. The
resulting SPF in spine 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 4.2.8, spine 22 constructs the
following sets:
|R = Prefix 111, Prefix 112, Prefix 121, Prefix 122
|H (for r=Prefix 111) = Node 111, Node 112
|H (for r=Prefix 112) = Node 111, Node 112
|H (for r=Prefix 121) = Node 121, Node 122
|H (for r=Prefix 122) = Node 121, Node 122
|A (for Spine 21) = Node 111, Node 112
With that and |H (for r=prefix 121) and |H (for r=prefix 122) being
disjoint from |A (for spine 21), spine 22 will originate an S-TIE
with prefix 121 and prefix 122, that is flooded to nodes 112, 112,
121 and 122.
5.4. Northbound Partitioned Router and Optional East-West Links
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. + + +
. X N1 | N2 | N3
. X | |
.+--+----+ +--+----+ +--+-----+
.| |0/0> <0/0| |0/0> <0/0| |
.| A01 +----------+ A02 +----------+ A03 | Level 1
.++-+-+--+ ++--+--++ +---+-+-++
. | | | | | | | | |
. | | +----------------------------------+ | | |
. | | | | | | | | |
. | +-------------+ | | | +--------------+ |
. | | | | | | | | |
. | +----------------+ | +-----------------+ |
. | | | | | | | | |
. | | +------------------------------------+ | |
. | | | | | | | | |
.++-+-+--+ | +---+---+ | +-+---+-++
.| | +-+ +-+ | |
.| L01 | | L02 | | L03 | Level 0
.+-------+ +-------+ +--------+
Figure 13: North Partitioned Router
Figure 13 shows a part of a fabric where level 1 is horizontally
connected and A01 lost its only northbound adjacency. Based on N-SPF
rules in Section 4.2.5.1 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. Moreover,
based on Section 4.3.12 it may advertise its loopback address as
south PGP to remain reachable "from the south" for operational
purposes. This is necessary since A02 will NOT route towards A01
using the E-W link (doing otherwise may form routing loops).
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 4.2.3.7. Moreover, A02 may now inject its loopback address
as south PGP.
6. Implementation and Operation: Further Details
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6.1. Considerations for Leaf-Only Implementation
Ideally RIFT can be stretched out 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:
1. Under normal conditions, the leaf needs to support a multipath
default route only. In worst 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 flooding reduction and de-
aggregation.
4. Unless optional leaf-2-leaf procedures are desired default route
origination, S-TIE origination is unnecessary.
6.2. Adaptations to Other Proposed Data Center Topologies
. +-----+ +-----+
. | | | |
.+-+ S0 | | S1 |
.| ++---++ ++---++
.| | | | |
.| | +------------+ |
.| | | +------------+ |
.| | | | |
.| ++-+--+ +--+-++
.| | | | |
.| | A0 | | A1 |
.| +-+--++ ++---++
.| | | | |
.| | +------------+ |
.| | +-----------+ | |
.| | | | |
.| +-+-+-+ +--+-++
.+-+ | | |
. | L0 | | L1 |
. +-----+ +-----+
Figure 14: 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 3 will not be met anymore. As an
example, shortcutting levels illustrated in Figure 14 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.
6.3. Originating Non-Default Route Southbound
Obviously, an implementation may choose to originate southbound
instead of a strict default route (as described in Section 4.2.3.7) a
shorter prefix P' but in such a scenario all addresses carried within
the RIFT domain must be contained within P'.
7. Security Considerations
The protocol has provisions for nonces and can include authentication
mechanisms in the future comparable to [RFC5709] and [RFC7987].
One can consider additionally 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 can implement a strategy of e.g. discarding contents of all
TIEs of nodes that were not present in the SPF tree over a certain
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.
Section 4.2.9 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
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southbound topology. Session authentication mechanisms are necessary
in environments where this is possible.
8. IANA Considerations
This specification will request at an opportune time multiple
registry points to exchange protocol packets in a standardized way,
amongst them multicast address assignments and standard port numbers.
The schema itself defines many values and codepoints which can be
considered registries themselves.
9. Acknowledgments
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 and Krzysztof Szarkowicz
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 sounding board in regard
to modern protocol implementation techniques RIFT is exploring.
Barak Gafni formalized first time clearly the problem of partitioned
spine on a (clean) napkin in Singapore.
10. References
10.1. Normative References
[I-D.ietf-6lo-rfc6775-update]
Thubert, P., Nordmark, E., Chakrabarti, S., and C.
Perkins, "Registration Extensions for 6LoWPAN Neighbor
Discovery", draft-ietf-6lo-rfc6775-update-21 (work in
progress), June 2018.
[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.
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[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>.
[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>.
[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>.
[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>.
[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>.
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[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>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/info/rfc6234>.
[RFC6822] Previdi, S., Ed., Ginsberg, L., Shand, M., Roy, A., and D.
Ward, "IS-IS Multi-Instance", RFC 6822,
DOI 10.17487/RFC6822, December 2012,
<https://www.rfc-editor.org/info/rfc6822>.
[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>.
[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>.
[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>.
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10.2. 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.
[FATTREE] Leiserson, C., "Fat-Trees: Universal Networks for
Hardware-Efficient Supercomputing", 1985.
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing
Architecture", draft-ietf-spring-segment-routing-15 (work
in progress), January 2018.
[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.
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[MAKSIC2013]
Maksic et al., N., "Improving Utilization of Data Center
Networks", IEEE Communications Magazine, Nov 2013.
[PROTOBUF]
Google, Inc., "Protocol Buffers,
https://developers.google.com/protocol-buffers".
[QUIC] Iyengar et al., J., "QUIC: A UDP-Based Multiplexed and
Secure Transport", 2016.
[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>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <https://www.rfc-editor.org/info/rfc3315>.
[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>.
[VAHDAT08]
Al-Fares, M., Loukissas, A., and A. Vahdat, "A Scalable,
Commodity Data Center Network Architecture", SIGCOMM ,
2008.
Appendix A. Information Elements Schema
This section introduces the schema for information elements.
On schema changes that
1. change field numbers or
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2. add new required fields or
3. remove fields or
4. change lists into sets, unions into structures or
5. change multiplicity of fields or
6. changes name of any field or
7. change datatypes of any field or
8. adds, changes or removes a default value of any field or
9. removes or changes any defined constant or constant value
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 of a structure
type without a default does not cause a major version increase even
if the fields inside the structure are optional with defaults.
Thrift serializer/deserializer MUST not discard optional, unknown
fields but preserve and serialize them again when re-flooding whereas
missing optional fields MAY be replaced with according default values
if present.
All signed integer as forced by 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.
A.1. common.thrift
/**
Thrift file with common definitions for RIFT
*/
/** @note MUST be interpreted in implementation as unsigned 64 bits.
* The implementation SHOULD NOT use the MSB.
*/
typedef i64 SystemIDType
typedef i32 IPv4Address
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/** this has to be of length long enough to accomodate prefix */
typedef binary IPv6Address
/** @note MUST be interpreted in implementation as unsigned 16 bits */
typedef i16 UDPPortType
/** @note MUST be interpreted in implementation as unsigned 32 bits */
typedef i32 TIENrType
/** @note MUST be interpreted in implementation as unsigned 32 bits */
typedef i32 MTUSizeType
/** @note MUST be interpreted in implementation as unsigned 32 bits */
typedef i32 SeqNrType
/** @note MUST be interpreted in implementation as unsigned 32 bits */
typedef i32 LifeTimeInSecType
/** @note MUST be interpreted in implementation as unsigned 16 bits */
typedef i16 LevelType
/** @note MUST be interpreted in implementation as unsigned 32 bits */
typedef i32 PodType
/** @note MUST be interpreted in implementation as unsigned 16 bits */
typedef i16 VersionType
/** @note MUST be interpreted in implementation as unsigned 32 bits */
typedef i32 MetricType
/** @note MUST be interpreted in implementation as unstructured 64 bits */
typedef i64 RouteTagType
/** @note MUST be interpreted in implementation as unstructured 32 bits
label value */
typedef i32 LabelType
/** @note MUST be interpreted in implementation as unsigned 32 bits */
typedef i32 BandwithInMegaBitsType
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 */
typedef i64 NonceType
/** adjacency holdtime */
typedef i16 HoldTimeInSecType
/** 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 */
struct IEEE802_1ASTimeStampType {
1: required i64 AS_sec;
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2: optional i32 AS_nsec;
}
/** Flags indicating nodes behavior in case of ZTP and support
for special optimization procedures. It will force level to `leaf_level`
*/
enum LeafIndications {
leaf_only =0,
leaf_only_and_leaf_2_leaf_procedures =1,
}
/** 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
/** This MUST be used when node is configured as superspine in ZTP.
This is kept reasonably low to alow for fast ZTP convergence on
failures. */
const LevelType default_superspine_level = 24
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
/** any element with 0 distance will be ignored,
* missing metrics will be replaced with default_distance
*/
const MetricType invalid_distance = 0
const bool overload_default = false
const bool flood_reduction_default = true
const HoldTimeInSecType default_holdtime = 3
/** by default LIE levels are ZTP offers */
const bool default_not_a_ztp_offer = false
/** by default e'one is repeating flooding */
const bool default_you_are_not_flood_repeater = false
/** 0 is illegal for SystemID */
const SystemIDType IllegalSystemID = 0
/** empty set of nodes */
const set<SystemIDType> empty_set_of_nodeids = {}
/** default UDP port to run LIEs on */
const UDPPortType default_lie_udp_port = 911
/** default UDP port to receive TIEs on, that can be peer specific */
const UDPPortType default_tie_udp_flood_port = 912
/** default MTU link size to use */
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const MTUSizeType default_mtu_size = 1400
/** indicates whether the direction is northbound/east-west
* or southbound */
enum TieDirectionType {
Illegal = 0,
South = 1,
North = 2,
DirectionMaxValue = 3,
}
enum AddressFamilyType {
Illegal = 0,
AddressFamilyMinValue = 1,
IPv4 = 2,
IPv6 = 3,
AddressFamilyMaxValue = 4,
}
struct IPv4PrefixType {
1: required IPv4Address address;
2: required PrefixLenType prefixlen;
}
struct IPv6PrefixType {
1: required IPv6Address address;
2: required PrefixLenType prefixlen;
}
union IPAddressType {
1: optional IPv4Address ipv4address;
2: optional IPv6Address ipv6address;
}
union IPPrefixType {
1: optional IPv4PrefixType ipv4prefix;
2: optional IPv6PrefixType ipv6prefix;
}
/** @note: Sequence of a prefix. Comparison function:
if diff(timestamps) < 200msecs better transactionid wins
else better time wins
*/
struct PrefixSequenceType {
1: required IEEE802_1ASTimeStampType timestamp;
2: optional PrefixTransactionIDType transactionid;
}
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enum TIETypeType {
Illegal = 0,
TIETypeMinValue = 1,
/** first legal value */
NodeTIEType = 2,
PrefixTIEType = 3,
TransitivePrefixTIEType = 4,
PGPrefixTIEType = 5,
KeyValueTIEType = 6,
TIETypeMaxValue = 7,
}
/** @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
*
* @todo: external routes
*/
enum RouteType {
Illegal = 0,
RouteTypeMinValue = 1,
/** First legal value. */
/** Discard routes are most prefered */
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,
/** advertised in S-TIEs */
SouthPrefix = 7,
/** transitive southbound are least preferred */
TransitiveSouthPrefix = 8,
RouteTypeMaxValue = 9
}
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A.2. encoding.thrift
/**
Thrift file for packet encodings for RIFT
*/
include "common.thrift"
/** represents protocol encoding schema major version */
const i32 protocol_major_version = 11
/** represents protocol encoding schema minor version */
const i32 protocol_minor_version = 0
/** common RIFT packet header */
struct PacketHeader {
1: required common.VersionType major_version = protocol_major_version;
2: required common.VersionType minor_version = protocol_minor_version;
/** this is the node sending the packet, in case of LIE/TIRE/TIDE
also the originator of it */
3: required common.SystemIDType sender;
/** level of the node sending the packet, required on everything except
* LIEs. Lack of presence on LIEs indicates UNDEFINED_LEVEL and is used
* in ZTP procedures.
*/
4: optional common.LevelType level;
}
/** Community serves as community for PGP purposes */
struct Community {
1: required i32 top;
2: required i32 bottom;
}
/** Neighbor structure */
struct Neighbor {
1: required common.SystemIDType originator;
2: required common.LinkIDType remote_id;
}
/** Capabilities the node supports */
struct NodeCapabilities {
/** can this node participate in flood reduction */
1: optional bool flood_reduction =
common.flood_reduction_default;
/** does this node restrict itself to be leaf only (in ZTP) and
does it support leaf-2-leaf procedures */
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2: optional common.LeafIndications leaf_indications;
}
/** RIFT LIE packet
@note this node's level is already included on the packet header */
struct LIEPacket {
/** optional 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;
/** this will reflect the neighbor once received to provid
3-way connectivity */
5: optional Neighbor neighbor;
6: optional common.PodType pod = common.default_pod;
/** optional nonce used for security computations */
7: optional common.NonceType nonce;
/** optional 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.
*/
8: optional NodeCapabilities capabilities;
/** required holdtime of the adjacency, i.e. how much time
MUST expire without LIE for the adjacency to drop
*/
9: required common.HoldTimeInSecType holdtime =
common.default_holdtime;
/** indicates that the level on the LIE MUST NOT be used
to derive a ZTP level by the receiving node. */
10: optional bool not_a_ztp_offer =
common.default_not_a_ztp_offer;
/** indicates to northbound neighbor that it should not
be reflooding this node's N-TIEs to flood reduce and
balance northbound flooding. To be ignored if received from a
northbound adjacency. */
11: optional bool you_are_not_flood_repeater=
common.default_you_are_not_flood_repeater;
/** optional downstream assigned locally significant label
value for the adjacency. */
12: optional common.LabelType label;
}
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/** 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;
/** more properties of the link can go in here */
}
/** 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 {
/** indicates direction of the TIE */
1: required common.TieDirectionType direction;
/** indicates originator of the TIE */
2: required common.SystemIDType originator;
3: required common.TIETypeType tietype;
4: required common.TIENrType tie_nr;
}
/** Header of a TIE */
struct TIEHeader {
2: required TIEID tieid;
3: required common.SeqNrType seq_nr;
/** lifetime expires down to 0 just like in ISIS */
4: required common.LifeTimeInSecType lifetime;
}
/** A sorted TIDE packet, if unsorted, behavior is undefined */
struct TIDEPacket {
/** all 00s marks starts */
1: required TIEID start_range;
/** all FFs mark end */
2: required TIEID end_range;
/** _sorted_ list of headers */
3: required list<TIEHeader> headers;
}
/** A TIRE packet */
struct TIREPacket {
1: required set<TIEHeader> headers;
}
/** Neighbor of a node */
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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 {
/** 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 or
* visible in same level/having partition upper do not match
the behavior is undefined and a warning SHOULD be generated.
Neighbors can be distributed across multiple TIEs however if
the sets are disjoint.
@note: observe that absence of fields implies defined defaults
*/
struct NodeTIEElement {
1: required common.LevelType level;
/** if neighbor systemID repeats in other node TIEs of same node
the behavior is undefined. Equivalent to |A_(n,s)(N) in spec. */
2: required map<common.SystemIDType,
NodeNeighborsTIEElement> neighbors;
3: optional NodeCapabilities capabilities;
4: optional NodeFlags flags;
/** optional node name for easier operations */
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5: optional string name;
/** Nodes seen an the same level through reflection through nodes
having backlink to both nodes. They are equivalent to |V(N) in
future specifications. Ignored in Node S-TIEs if present.
*/
6: optional set<common.SystemIDType> visible_in_same_level
= common.empty_set_of_nodeids;
/** Non-overloaded nodes in |V seen as attached to another north
* level partition due to the fact that some nodes in its |V have
* adjacencies to higher level nodes that this node doesn't see.
* This may be used in the computation at higher levels to prevent
* blackholing. Ignored in Node S-TIEs if present.
* Equivalent to |PUL(N) in spec. */
7: optional set<common.SystemIDType> same_level_unknown_north_partitions
= common.empty_set_of_nodeids;
}
struct PrefixAttributes {
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;
/** optional monotonic clock for mobile addresses */
4: optional common.PrefixSequenceType monotonic_clock;
}
/** multiple 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;
}
/** keys with their values */
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.
*/
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union TIEElement {
/** in case of enum common.TIETypeType.NodeTIEType */
1: optional NodeTIEElement node;
/** in case of enum common.TIETypeType.PrefixTIEType */
2: optional PrefixTIEElement prefixes;
/** transitive prefixes (always southbound) which SHOULD be propagated
* southwards towards lower levels to heal
* pathological upper level partitioning, otherwise
* blackholes may occur. MUST NOT be advertised within a North TIE.
*/
3: optional PrefixTIEElement transitive_prefixes;
4: optional KeyValueTIEElement keyvalues;
/** @todo: policy guided prefixes */
}
/** @todo: flood header separately in UDP to allow changing lifetime and SHA
without reserialization
*/
struct TIEPacket {
1: required TIEHeader header;
2: required TIEElement element;
}
union PacketContent {
1: optional LIEPacket lie;
2: optional TIDEPacket tide;
3: optional TIREPacket tire;
4: optional TIEPacket tie;
}
/** protocol packet structure */
struct ProtocolPacket {
1: required PacketHeader header;
2: required PacketContent content;
}
Appendix B. Finite State Machines
All FSM figures are provided as [DOT] description due to limiations
of ASCII art.
B.1. LIE
digraph G791bb566f5cf48b09e26193a727dadfd {
N91ea7c47496746d880c10a5def7874c2[label="TwoWay"][shape="oval"];
Nc5d62000e5dc45a9ac1379c28cfda9b3[label="OneWay"][shape="oval"];
Nd7b87acca28f4613a68bbc4ef79a3c50[label="Enter"][style="dashed"]
[shape="plain"];
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Ne0fb2564cd334a44ad080f73b07cca86[label="ThreeWay"][shape="oval"];
N51443826b9c84d8b83cc252b471047c9[label="Enter"][style="invis"]
[shape="plain"];
N19343f3f3a9b41c29f3ac23c8dccc179[label="Exit"][style="invis"]
[shape="plain"];
N91ea7c47496746d880c10a5def7874c2 -> Nc5d62000e5dc45a9ac1379c28cfda9b3
[label="|LevelChanged|"][color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Ne0fb2564cd334a44ad080f73b07cca86 -> Ne0fb2564cd334a44ad080f73b07cca86
[label="|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"][arrowhead="normal" dir="both" arrowtail="none"];
Nc5d62000e5dc45a9ac1379c28cfda9b3 -> N91ea7c47496746d880c10a5def7874c2
[label="|NewNeighbor|"][color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
Ne0fb2564cd334a44ad080f73b07cca86 -> N91ea7c47496746d880c10a5def7874c2
[label="|NeighborDroppedReflection|"][color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
Nc5d62000e5dc45a9ac1379c28cfda9b3 -> Nc5d62000e5dc45a9ac1379c28cfda9b3
[label="|TimerTick|\n|LieRcvd|\n|UnacceptableHeader|\n|HoldtimeExpired|\n|SendLie|"]
[color="black"][arrowhead="normal" dir="both" arrowtail="none"];
N91ea7c47496746d880c10a5def7874c2 -> Ne0fb2564cd334a44ad080f73b07cca86
[label="|ValidReflection|"][color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
Nd7b87acca28f4613a68bbc4ef79a3c50 -> Nc5d62000e5dc45a9ac1379c28cfda9b3
[label=""]
[color="black"][arrowhead="normal" dir="both" arrowtail="none"];
N91ea7c47496746d880c10a5def7874c2 -> N91ea7c47496746d880c10a5def7874c2
[label="|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"][arrowhead="normal" dir="both" arrowtail="none"];
Nc5d62000e5dc45a9ac1379c28cfda9b3 -> Nc5d62000e5dc45a9ac1379c28cfda9b3
[label="|LevelChanged|\n|HALChanged|\n|HATChanged|\n|HALSChanged|\n|UpdateZTPOffer|"]
[color="blue"][arrowhead="normal" dir="both" arrowtail="none"];
N91ea7c47496746d880c10a5def7874c2 -> N91ea7c47496746d880c10a5def7874c2
[label="|TimerTick|\n|LieRcvd|\n|SendLie|"][color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
Ne0fb2564cd334a44ad080f73b07cca86 -> Nc5d62000e5dc45a9ac1379c28cfda9b3
[label="|NeighborChangedLevel|\n|NeighborChangedAddress|\n|UnacceptableHeader|\n|HoldtimeExpired|\n|MultipleNeighbors|"]
[color="black"][arrowhead="normal" dir="both" arrowtail="none"];
Ne0fb2564cd334a44ad080f73b07cca86 -> Nc5d62000e5dc45a9ac1379c28cfda9b3
[label="|LevelChanged|"][color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Ne0fb2564cd334a44ad080f73b07cca86 -> Ne0fb2564cd334a44ad080f73b07cca86
[label="|TimerTick|\n|LieRcvd|\n|SendLie|"][color="black"]
[arrowhead="normal" dir="both" arrowtail="none"];
N91ea7c47496746d880c10a5def7874c2 -> Nc5d62000e5dc45a9ac1379c28cfda9b3
[label="|NeighborChangedLevel|\n|NeighborChangedAddress|\n|UnacceptableHeader|\n|HoldtimeExpired|\n|MultipleNeighbors|"]
[color="black"][arrowhead="normal" dir="both" arrowtail="none"];
}
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LIE 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
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 HoldtimeExpired: adjacency hold down expired
o MultipleNeighbors: more than one neighbor seen on interface
o LIECorrupt: corrupted LIE seen
o SendLie: send a LIE out
o UpdateZTPOffer: update this node's ZTP offer
Actions
on UpdateZTPOffer in TwoWay finishes in TwoWay: send offer to ZTP
FSM
on HALChanged in OneWay finishes in OneWay: store new HAL
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on HALChanged in ThreeWay finishes in ThreeWay: store new HAL
on HoldtimeExpired in OneWay finishes in OneWay: no action
on UpdateZTPOffer in OneWay finishes in OneWay: send offer to ZTP
FSM
on LevelChanged in ThreeWay finishes in OneWay: update level with
event value
on MultipleNeighbors in TwoWay finishes in OneWay: no action
on NeighborChangedLevel in TwoWay finishes in OneWay: no action
on HATChanged in OneWay finishes in OneWay: store HAT
on HATChanged in ThreeWay finishes in ThreeWay: store HAT
on MultipleNeighbors in ThreeWay finishes in OneWay: no action
on SendLie in ThreeWay finishes in ThreeWay: SENDLIE
on TimerTick in TwoWay finishes in TwoWay: PUSH SendLie event, if
holdtime expired PUSH HoldtimeExpired event
on HALSChanged in OneWay finishes in OneWay: store HALS
on SendLie in OneWay finishes in OneWay: SENDLIE
on LevelChanged in TwoWay finishes in OneWay: update level with
event value
on LieRcvd in TwoWay finishes in TwoWay: PROCESS_LIE
on HALSChanged in ThreeWay finishes in ThreeWay: store HALS
on UpdateZTPOffer in ThreeWay finishes in ThreeWay: send offer to
ZTP FSM
on HALSChanged in TwoWay finishes in TwoWay: store HALS
on LieRcvd in OneWay finishes in OneWay: PROCESS_LIE
on NeighborChangedLevel in ThreeWay 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 UnacceptableHeader in ThreeWay finishes in OneWay: no action
on SendLie in TwoWay finishes in TwoWay: SENDLIE
on LevelChanged in OneWay finishes in OneWay: update level with
event value, PUSH SendLie event
on NeighborChangedAddress in ThreeWay finishes in OneWay: no
action
on HALChanged in TwoWay finishes in TwoWay: store new HAL
on NewNeighbor in OneWay finishes in TwoWay: PUSH SendLie event
on ValidReflection in TwoWay finishes in ThreeWay: no action
on UnacceptableHeader in TwoWay finishes in OneWay: no action
on LieRcvd in ThreeWay finishes in ThreeWay: PROCESS_LIE
on NeighborDroppedReflection in ThreeWay finishes in TwoWay: no
action
on NeighborChangedAddress in TwoWay finishes in OneWay: no action
on HoldtimeExpired in ThreeWay finishes in OneWay: no action
on HATChanged in TwoWay finishes in TwoWay: store HAT
on UnacceptableHeader in OneWay finishes in OneWay: no action
on TimerTick in OneWay finishes in OneWay: PUSH SendLie event
on Entry into OneWay: CLEANUP and then process event SendLie
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. SENDLIE: 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 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
3. 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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B.2. ZTP
digraph G04743cd825cc40c5b93de0616ffb851b {
N29e7db3976644f62b6f3b2801bccb854[label="Enter"]
[style="dashed"][shape="plain"];
N33df4993a1664be18a2196001c27a64c[label="HoldingDown"][shape="oval"];
N839f77189e324c82b21b8a709b4b021d[label="ComputeBestOffer"][shape="oval"];
Nc97f2b02808d4751afcc630687bf7421[label="UpdatingClients"][shape="oval"];
N7ad21867360c44709be20a99f33dd1f7[label="Enter"]
[style="dashed"][shape="plain"];
N33df4993a1664be18a2196001c27a64c -> N33df4993a1664be18a2196001c27a64c
[label="|ComputationDone|"][color="green"]
[arrowhead="normal" dir="both" arrowtail="none"];
N29e7db3976644f62b6f3b2801bccb854 -> Nc97f2b02808d4751afcc630687bf7421
[label=""]
[color="black"][arrowhead="normal" dir="both" arrowtail="none"];
N839f77189e324c82b21b8a709b4b021d -> N839f77189e324c82b21b8a709b4b021d
[label="|NeighborOffer|\n|WithdrawNeighborOffer|"]
[color="blue"][arrowhead="normal" dir="both" arrowtail="none"];
N33df4993a1664be18a2196001c27a64c -> N839f77189e324c82b21b8a709b4b021d
[label="|ChangeLocalLeafIndications|\n|ChangeLocalConfiguredLevel|"]
[color="gold"]
[arrowhead="normal" dir="both" arrowtail="none"];
N839f77189e324c82b21b8a709b4b021d -> N839f77189e324c82b21b8a709b4b021d
[label="|BetterHAL|\n|BetterHAT|\n|LostHAT|"]
[color="red"][arrowhead="normal" dir="both" arrowtail="none"];
N33df4993a1664be18a2196001c27a64c -> N33df4993a1664be18a2196001c27a64c
[label="|NeighborOffer|\n|WithdrawNeighborOffer|"][color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
Nc97f2b02808d4751afcc630687bf7421 -> N839f77189e324c82b21b8a709b4b021d
[label="|BetterHAL|\n|BetterHAT|\n|LostHAT|"][color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
N33df4993a1664be18a2196001c27a64c -> N33df4993a1664be18a2196001c27a64c
[label="|ShortTic|"][color="black"][arrowhead="normal" dir="both"
arrowtail="none"];
Nc97f2b02808d4751afcc630687bf7421 -> Nc97f2b02808d4751afcc630687bf7421
[label="|NeighborOffer|\n|WithdrawNeighborOffer|"][color="blue"]
[arrowhead="normal" dir="both" arrowtail="none"];
N33df4993a1664be18a2196001c27a64c -> N33df4993a1664be18a2196001c27a64c
[label="|BetterHAL|\n|BetterHAT|\n|LostHAL|\n|LostHAT|"][color="red"]
[arrowhead="normal" dir="both" arrowtail="none"];
N839f77189e324c82b21b8a709b4b021d -> N33df4993a1664be18a2196001c27a64c
[label="|LostHAL|"][color="red"][arrowhead="normal" dir="both"
arrowtail="none"];
N7ad21867360c44709be20a99f33dd1f7 -> N839f77189e324c82b21b8a709b4b021d
[label=""][color="black"][arrowhead="normal" dir="both" arrowtail="none"];
N839f77189e324c82b21b8a709b4b021d -> Nc97f2b02808d4751afcc630687bf7421
[label="|ComputationDone|"][color="green"][arrowhead="normal" dir="both"
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arrowtail="none"];
N839f77189e324c82b21b8a709b4b021d -> N839f77189e324c82b21b8a709b4b021d
[label="|ChangeLocalLeafIndications|\n|ChangeLocalConfiguredLevel|"]
[color="gold"]
[arrowhead="normal" dir="both" arrowtail="none"];
Nc97f2b02808d4751afcc630687bf7421 -> N33df4993a1664be18a2196001c27a64c
[label="|LostHAL|"]
[color="red"][arrowhead="normal" dir="both" arrowtail="none"];
N33df4993a1664be18a2196001c27a64c -> N839f77189e324c82b21b8a709b4b021d
[label="|HoldDownExpired|"][color="green"][arrowhead="normal" dir="both"
arrowtail="none"];
Nc97f2b02808d4751afcc630687bf7421 -> N839f77189e324c82b21b8a709b4b021d
[label="|ChangeLocalLeafIndications|\n|ChangeLocalConfiguredLevel|"]
[color="gold"]
[arrowhead="normal" dir="both" arrowtail="none"];
}
LIE FSM DOT
Events
o ChangeLocalLeafIndications: node configured with new leaf flags
o ChangeLocalConfiguredLevel: node locally configured with a defined
level
o NeighborOffer: a new neighbor offer with optional level and
neighbor state
o WithdrawNeighborOffer: a neighbor's offer withdrawn
o BetterHAL: better HAL computed internally
o BetterHAT: better HAT computed internally
o LostHAL: lost last HAL in computation
o LostHAT: lost HAT in computation
o ComputationDone: computation performed
o HoldDownExpired: holddown expired
Actions
on LostHAT in ComputeBestOffer finishes in ComputeBestOffer:
LEVEL_COMPUTE
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on LostHAT in HoldingDown finishes in HoldingDown: no action
on LostHAL in HoldingDown finishes in HoldingDown:
on ChangeLocalLeafIndications in UpdatingClients finishes in
ComputeBestOffer: store leaf flags
on LostHAT in UpdatingClients finishes in ComputeBestOffer: no
action
on BetterHAT in HoldingDown finishes in HoldingDown: no action
on NeighborOffer in ComputeBestOffer finishes in ComputeBestOffer:
if no level offered REMOVE_OFFER else
if level > leaf then UPDATE_OFFER else REMOVE_OFFER
on BetterHAT in UpdatingClients finishes in ComputeBestOffer: no
action
on ChangeLocalConfiguredLevel in HoldingDown finishes in
ComputeBestOffer: store level
on BetterHAL in ComputeBestOffer finishes in ComputeBestOffer:
LEVEL_COMPUTE
on HoldDownExpired in HoldingDown finishes in ComputeBestOffer:
PURGE_OFFERS
on ShortTic in HoldingDown finishes in HoldingDown: if holddown
timer expired PUSH_EVENT HoldDownExpired
on ComputationDone in ComputeBestOffer finishes in
UpdatingClients: no action
on LostHAL in UpdatingClients finishes in HoldingDown: if any
southbound adjacencies present update holddown timer to normal
duration else fire holddown timer immediately
on NeighborOffer in UpdatingClients finishes in UpdatingClients:
if no level offered REMOVE_OFFER else
if level > leaf then UPDATE_OFFER else REMOVE_OFFER
on ChangeLocalConfiguredLevel in ComputeBestOffer finishes in
ComputeBestOffer: store level and LEVEL_COMPUTE
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on NeighborOffer in HoldingDown finishes in HoldingDown:
if no level offered REMOVE_OFFER else
if level > leaf then UPDATE_OFFER else REMOVE_OFFER
on LostHAL in ComputeBestOffer finishes in HoldingDown: if any
southbound adjacencies present update holddown timer to normal
duration else fire holddown timer immediately
on BetterHAT in ComputeBestOffer finishes in ComputeBestOffer:
LEVEL_COMPUTE
on WithdrawNeighborOffer in ComputeBestOffer finishes in
ComputeBestOffer: REMOVE_OFFER
on ChangeLocalLeafIndications in ComputeBestOffer finishes in
ComputeBestOffer: store leaf flags and LEVEL_COMPUTE
on BetterHAL in HoldingDown finishes in HoldingDown: no action
on WithdrawNeighborOffer in HoldingDown finishes in HoldingDown:
REMOVE_OFFER
on ChangeLocalLeafIndications in HoldingDown finishes in
ComputeBestOffer: store leaf flags
on ChangeLocalConfiguredLevel in UpdatingClients finishes in
ComputeBestOffer: store level
on ComputationDone in HoldingDown finishes in HoldingDown:
on BetterHAL in UpdatingClients finishes in ComputeBestOffer: no
action
on WithdrawNeighborOffer in UpdatingClients finishes in
UpdatingClients: REMOVE_OFFER
on Entry into UpdatingClients: update all LIE FSMs with
computation results
on Entry into ComputeBestOffer: LEVEL_COMPUTE
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
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2. COMPARE_OFFERS: checks whether based on current offers and held
last results the events BetterHAL/LostHAL/BetterHAT/LostHAT are
necessary and returns them
3. UPDATE_OFFER: store current offer and COMPARE_OFFERS, PUSH
according events
4. LEVEL_COMPUTE: compute best offered or configured level and HAL/
HAT, if anything changed PUSH ComputationDone
5. REMOVE_OFFER: remove the according offer and COMPARE_OFFERS, PUSH
according events
6. PURGE_OFFERS: REMOVE_OFFER for all held offers, COMPARE OFFERS,
PUSH according events
Appendix C. Constants
C.1. Configurable Protocol Constants
+-----------------+--------------+----------------------------------+
| | 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::0078 or all-rift-routers |
| Multicast | Value, | to be assigned in IPv6 Multicast |
| Address | Configurable | Address Assignments |
+-----------------+--------------+----------------------------------+
| LIE Destination | Default | 911 |
| Port | Value, | |
| | Configurable | |
+-----------------+--------------+----------------------------------+
| Level value for | Constant | 24 |
| SUPERSPINE_FLAG | | |
+-----------------+--------------+----------------------------------+
Table 5: all_constants
Authors' Addresses
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Tony Przygienda (editor)
Juniper Networks
1194 N. Mathilda Ave
Sunnyvale, CA 94089
US
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
Alia Atlas
Individual
Email: akatlas@juniper.net
John Drake
Juniper Networks
1194 N. Mathilda Ave
Sunnyvale, CA 94089
US
Email: jdrake@juniper.net
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