This document describes the use of IS-IS and OSPF for discovering Resilient MPLS Rings (RMR). RMR relies on the IGP for discovery of the ring elements and properties, as well as subsequent changes to the ring topology. Details of auto-discovery and operation are given in the RMR architecture document; this document simply describes the formats of RMR-related constructs in IS-IS and OSPF.

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 [RFC2119].

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1. Introduction

Rings are a very common topology in transport networks. A ring is the simplest topology offering link and node resilience. Rings are nearly ubiquitous in access and aggregation networks. As MPLS increases its presence in such networks, and takes on a greater role in transport, it is imperative that MPLS handles rings well; this is not the case today. The RMR architecture document [I-D.ietf-mpls-rmr] describes the motivations and operation of RMR.

RMR uses protocols such as IS-IS [RFC5305] and OSPF[RFC3630] for auto-discovery, and RSVP-TE [RFC3209] and LDP [RFC5036] for signaling LSPs. This document gives the specifics of Type-Length-Value (TLV) formats for IS-IS and OSPF.

1.1. Definitions


                  R0 . . . R1                 
                .             .               
             R7                 R2            
Anti-     |  .        Ring       .  |         
Clockwise |  .                   .  | Clockwise
          v  .      RID = 17     .  v         
             R6                 R3            
                .             .               
                  R5 . . . R4

Figure 1: Ring with 8 nodes

A ring is a subgraph of a given graph G = (V, E), consisting of a subset of n nodes {R_i, 0 ≤ i < n}. The directed edges {(R_i, R_i+1) and (R_i+1, R_i), 0 ≤ i < n-1} must be a subset of E (note that index arithmetic is done modulo n). We define the direction from node R_i to R_i+1 as "clockwise" (CW) and the reverse direction as "anticlockwise" (AC). As there may be several rings in a graph, we number each ring with a distinct ring ID RID.

The following terminology is used for ring LSPs:

Ring ID (RID):

A non-zero number that identifies a ring; this is unique in some scope of a Service Provider's network. A node may belong to multiple rings.

Ring node:

A member of a ring. Note that a device may belong to several rings.

Node index:

A logical numbering of nodes in a ring, from zero upto one less than the ring size. Used purely for exposition in this document.

Ring master:

The ring master initiates the ring identification process. Mastership is indicated in the IGP by a two-bit field.

Ring neighbors:

Nodes whose indices differ by one (modulo ring size).

Ring links:

Links that connnect ring neighbors.

Express links:

Links that connnect non-neighboring ring nodes.

Ring direction:

A two-bit field in the IGP indicating the direction of a link. The choices are:

UN: 00: undefined link
CW: 01: clockwise ring link
AC: 10: anticlockwise ring link
EX: 11: express link

Ring Identification:

The process of discovering ring nodes, ring links, link directions, and express links.

The following notation is used for ring LSPs:

R_k:: A ring node with index k. R_k has AC neighbor R_(k-1) and CW neighbor R_(k+1).
RL_k:: A (unicast) Ring LSP anchored on node R_k.
CL_jk:: A label allocated by R_j for RL_k in the CW direction.
AL_jk:: A label allocated by R_j for RL_k in the AC direction.
P_jk (Q_jk):: A Path (Resv) message sent by R_j for RL_k.

2. Theory of Operation

Say a ring has ring ID RID. The ring is provisioned by choosing one or more ring masters for the ring and assigning them the RID. Other nodes in the ring may also be assigned this RID, or may be configured as "promiscuous". Ring discovery then kicks in. When each ring node knows its CW and AC ring neighbors and its ring links, and all express links have been identified, ring identification is complete.

Once ring identification is complete, each node signals one or more ring LSPs RL_i. RL_i, anchored on node R_i, consists of two counter-rotating unicast LSPs that start and end at R_i. A ring LSP is "multipoint": any node R_j can use RL_i to send traffic to R_i; this can be in either the CW or AC directions, or both (i.e., load balanced). Both of these counter-rotating LSPs are "active"; the choice of direction to send traffic to R_i is determined by policy at the node where traffic is injected into the ring. The default is to send traffic along the shortest path. Bidirectional connectivity between nodes R_i and R_j is achieved by using two different ring LSPs: R_i uses RL_j to reach R_j, and R_j uses RL_i to reach R_i.

2.1. Provisioning

For the purposes of RMR, a ring node R is configured with its loopback address, the RID that it will participate in, and what link-state IGP to use for auto-discovery. R is also configured with a mastership value, which is used in master election. Finally, R may be configured with the signaling protocols and OAM protocols it supports, or these may be inferred. Note that R may participate in multiple rings; each would have its own configuration.

To simplify ring provisioning even further, R may be made "promiscuous" by being assigned an RID of 0. A promiscuous node listens to RIDs in its IGP neighbors' link-state updates in order to acquire an RID for its use. Details are in [I-D.ietf-mpls-rmr].

2.2. Announcement

[RMR Node Type][RMR Node Length][RID][Node Flags][sub-TLVs]

Ring Node TLV Structure

[RMR Nbr Type][RMR Nbr Length][Nbr Address][Nbr Flags]

Ring Neighbor Sub-TLV Structure

Once configured, R announces its configuration parameters in the IGP via an RMR Node TLV. The RMR Node TLV may contain sub-TLVs; in particular, the RMR Neighbor TLV. At a high level, these TLVs are as follows.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type (TBD)  | Length = 6+S  |       Ring ID (4 octets) ...  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      ... (RID continued)      |     Node Flags (2 octets)     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs, if any ... 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
S is the total size of the sub-TLVs

Ring Node TLV Format

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Type (TBD)  | Length = n*6  |      Neighbor Loopback ...    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... (continued, 4 octets)     |   Neighbor Flags (2 octets)   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                   Neighbor Loopback (4 octets)                |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Neighbor Flags (2 octets)   | (etc.)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
n = number of neighbors included in the sub-TLV

Ring Neighbor sub-TLV Format

In IS-IS, the RMR Node TLV is a new top-level TLV. The specific format is as follows:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Type (TBD)          |         Length = 8+S          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Ring ID (4 octets)                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Node Flags (2 octets)     |         Pad (2 octets)        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Pad is set to zero when sending and ignored on receipt.
S = total length of sub-TLVs

OSPF Ring Node TLV Format

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Type (TBD)          |         Length = 6*N          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                   Neighbor Loopback (4 octets)                |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    Neighbor Flags (2 octets)  |         Pad (2 octets)        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                   Neighbor Loopback (4 octets)                |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    Neighbor Flags (2 octets)  |         Pad (2 octets)        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  ... etc.                                                     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Pad is set to zero when sending and ignored on receipt.

OSPF Neighbor sub-TLV Format

 0                   1          
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MV |SS | SO  |    MBZ    |SU |M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
MV: Mastership Value
SS: Supported Signaling Protocols (10 = RSVP-TE; 01 = LDP)
SO: Supported OAM Protocols (100 = BFD; 010 = CFM; 001 = EFM)
SU: Signaling Protocol to Use  (00 = none; 01 = LDP; 10 = RSVP-TE)
M : Elected Master (0 = no, 1 = yes)

Flags for a Ring Node TLV

 0                   1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RD |OAM|          MBZ          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
RD:  Ring Direction
OAM: OAM Protocol to use (00 = none; 01 = BFD; 10 = CFM; 11 = EFM)

Flags for a Ring Neighbor TLV

In OSPF, the RMR Node TLV is a new top-level TLV of the Traffic Engineering Opaque LSA.

3. Security Considerations

It is not anticipated that either the notion of MPLS rings or the extensions to link-state IGPs to support them will cause new security loopholes. As this document is updated, this section will also be updated.

4. IANA Considerations

IANA is requested to assign a new top-level TLV for the RMR Node TLV from the IS-IS TLV Codepoints Registry. IANA is also requested to create a new registry for sub-TLVs of the RMR Node TLV.

IANA is also requested to assign a new top-level type for the RMR Node TLV from the OSPF TE TLVs Registry. IANA is also requested to create a new registry for sub-TLVs of the RMR Node TLV.

5. References

5.1. Normative References

[I-D.ietf-mpls-rmr]	Kompella, K. and L. Contreras, "Resilient MPLS Rings", Internet-Draft draft-ietf-mpls-rmr-03, October 2016.
[RFC2119]	Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.

5.2. Informative References

[RFC3209]	Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V. and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001.
[RFC3630]	Katz, D., Kompella, K. and D. Yeung, "Traffic Engineering (TE) Extensions to OSPF Version 2", RFC 3630, DOI 10.17487/RFC3630, September 2003.
[RFC5036]	Andersson, L., Minei, I. and B. Thomas, "LDP Specification", RFC 5036, DOI 10.17487/RFC5036, October 2007.
[RFC5305]	Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, DOI 10.17487/RFC5305, October 2008.

Author's Address

Kireeti Kompella Juniper Networks, Inc. 1133 Innovation Way Sunnyvale, CA 94089 USA EMail: kireeti.kompella@gmail.com

Abstract

Requirements Language

Status of This Memo

Copyright Notice

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