ISIS Working Group Dave Allan, Uma Chunduri
Internet Draft Ericsson
Intended status: Standards Track
Expires: December 2016
June 2016
IS-IS extensions for Computed Multicast applied to MPLS based
Segment Routing
draft-allan-isis-spring-multicast-00
Abstract
This document describes the IS-IS extensions required to support
multicast for MPLS based Segment Routing. In this approach IS-IS
speakers compute their role in multicast tree construction based on
the information in the IS-IS routing information base.
Status of this Memo
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Table of Contents
1. Introduction...................................................2
1.1. Authors......................................................2
1.2. Requirements Language........................................3
2. Conventions used in this document..............................3
2.1. Terminology..................................................3
3. Overview.......................................................3
4. New TLVs.......................................................4
4.1. Compute Capability TLV.......................................4
4.2. SRM SID Multicast Group Binding sub-TLV......................4
4.3. SRM Pinned Tree Descriptor sub-TLV...........................5
5. Acknowledgements...............................................7
6. Security Considerations........................................7
7. IANA Considerations............................................7
8. References.....................................................7
8.1. Normative References.........................................7
8.2. Informative References.......................................8
9. Authors' Addresses.............................................8
1. Introduction
[ALLAN-1] describes a solution for multicast for Segment Routing with
MPLS data plane in which source specific multicast distribution trees
(MDTs) are computed from information distributed via an IGP. Using
this approach, both any-source multicast (ASM) and engineered p2mp
trees can be supported.
This memo describes TLVs for IS-IS to support the segment routing
multicast approach as described in [ALLAN-1].
1.1. Authors
David Allan, Uma Chunduri
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1.2. 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 RFC2119 [RFC2119].
2. Conventions used in this document
2.1. Terminology
Candidate replication point - is a node will potentially need to
install state as determined at some intermediate step in MDT
computation. It will either resolve to having no role or a role as a
replication point once multicast has converged.
Candidate role - refers to any potential combination of roles on a
given MDT as determined at some intermediate step in MDT computation.
For example, a node with a candidate role may be a leaf and may be a
candidate replication point.
Downstream - refers to the direction along the shortest path to one
or more leaves for a given multicast distribution tree
Multicast convergence - is when all computation and state
installation to ensure the FIB reflects the multicast information in
the IGP is complete.
Pinned path - Is a unique shortest path extending from a leaf
upstream towards the root for a given MDT. Therefore is a component
of an MDT that must be there. It will not necessarily extend from the
leaf all the way to the root during intermediate computation steps. A
pinned path can result from pruning operations.
Role - refers specifically to a node that is either a root, a leaf or
a replication node for a given multicast distribution tree
Unicast convergence- is when all computation and state installation
to ensure the FIB reflects the unicast information in the IGP is
complete.
Upstream - refers to the direction along the shortest path to the
root of a given multicast distribution tree
3. Overview
[ALLAN-1] adds the concept of the multicast segment to the Segment
Routing architecture [IDSR].
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Extending the IS-IS to support multicast segments adds
synchronization of knowledge of: multicast SIDs, multicast group
membership and agreement on the algorithm to use for computation of
multicast distribution trees(MDTs) across the set of IS-IS speakers
in an area/domain. This document specifies the TLVs necessary for IS-
IS to support multicast segments in the Segment Routing architecture.
4. New TLVs
4.1. Compute Capability TLV
The presence of this sub-TLV in an LSP (TLV 144 defined in [RFC6329])
indicates both that the originating node supports computed spring
multicast, and the algorithm that is configured to be used for a
particular topology. All nodes supporting computed multicast are
required to agree on the algorithm for correct operation of the
network for that topology.
The format of the sub-TLV is:
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= SRM-CAP | = TBD IANA
+-+-+-+-+-+-+-+-+
| Length | (1 byte)
+-+-+-+-+-+-+-+-+-------------------------------+---------------+
| Algorithm OUI (24 bits) | Algorithm ID |
+-----------------------------------------------+---------------+
Where:
The upper 24 bits contains an organizationally unique identifier (as
per [RFC7042]) and the lower 8 bits contains an algorithm identifier.
The default algorithm supported as per [ALLAN-1] is identified by
Algorithm OUI = 0x008037 (Ericsson), Algorithm ID = 0x01 (default).
4.2. SRM SID Multicast Group Binding sub-TLV
The SID Multicast Group Binding sub-TLV communicates the binding
between the SID specific to the MDT for the multicast group
originating at the advertising node and the multicast group address
as well as transmit and receive interest for the advertising node.
Note that if the TLV does not have the T bit set, the SID TLV is not
included in the message. The encoding is as a sub-TLV from the 135,
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235, 236 and 237 registry. This sub-TLV SHOULD be advertised when N
bit set in the IPv4/IPv6 Extended Reachability Attribute Flags for
the corresponding prefix as defined in [RFC7794]. The encoding of
the SID sub-TLV is as per section 2.3 of [SPRING-ISIS].
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 | Length |T|R| Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| Group Address |
. . . .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID sub-TLV (when T Bit is set) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type = TBD (IANA assignment from TLV 135, 235, 236 and 237
registry)
Length = 8 octet Variable which includes size of the T/R, reserved
fields, multicast group address and the SID TLV
T-bit indicates that this node is a source for the multicast group
specified in the sub-tlv.
R-bit indicates that this node is a receiver for the multicast
group specified in the sub-tlv.
Group address = 4 octet IPv4 multicast group address (when used
with TLV 135 or 235), 16 octet IPv6 multicast group address (when
used with TLV 236 or 237).
SID sub-TLV contains the segment ID to use for this multicast
segment.
4.3. SRM Pinned Tree Descriptor sub-TLV
The pinned tree descriptor defines all nodes that have a role in a
multicast distribution tree, and their relationship to the individual
multicast segments that define the tree. The encoding is an
unstructured list, where if the tree description exceeds 252 bytes,
it may simply use more than one sub-TLV. This sub-TLV SHOULD be
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advertised when N bit set in the IPv4/IPv6 Extended Reachability
Attribute Flags for the corresponding prefix as defined in [RFC7794].
The encoding of a role descriptor is in the form of
upstream_SID/unicast_SID/downstream _SID, where each of the SIDs is
encoded as a sub-TLV as per [SPRING-ISIS].
The root of the MDT (and originator of the TLV) will have a NULL
upstream SID, transit waypoints will have both a defined upstream and
downstream multicast segment SID, and a leaf will have a NULL
downstream SID. The unicast SID corresponds to the node for which the
entry defines its role.
+-+-+-+-+-+-+-+-+
| Type=SRM-PTD | = TBD IANA
+-+-+-+-+-+-+-+-+
| Length | (1 byte)
+-+-+-+-+-+-+-+-+-------------------------------------+
| role descriptor 1 |
+-----------------------------------------------------+
| role descriptor 2 |
+-----------------------------------------------------+
| role descriptor 3 |
+-----------------------------------------------------+
. . . .
+-----------------------------------------------------+
| role descriptor n |
+-----------------------------------------------------+
Where:
Type = TBD (IANA assignment from TLV 135, 235, 236 and 237
registry)
Length = Variable and represents size of the role descriptors
The encoding of a role descriptor is in the form:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Upstream Multicast SID sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unicast SID sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Multicast SID sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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5. Acknowledgements
6. Security Considerations
For a future version of this document.
7. IANA Considerations
This memo requires the allocation of:
1) a value for each of the SRM SID Multicast Group Binding sub-TLV,
and the SRM Pinned Tree Descriptor sub-TLV from the "Sub-TLVs for
TLVs 135, 235, 236, and 237" registry.
2) A value for the SRM Capability sub-TLV from the "Sub-TLVs for TLV
144" registry.
8. References
8.1. Normative References
[IS-IS] ISO/IEC 10589:2002, Second Edition, "Intermediate System
to Intermediate System Intra-Domain Routing Exchange
Protocol for use in Conjunction with the Protocol for
Providing the Connectionless-mode Network Service (ISO
8473)", 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6329] Fedyk et.al. "IS-IS Extensions Supporting IEEE 802.1aq
Shortest Path Bridging", IETF RFC 6329, April 2012
[RFC7042] Eastlake, D. et. al.,"IANA Considerations and IETF
Protocol and Documentation Usage for IEEE 802
Parameters", IETF RFC 7042, October 2013
[RFC7794] Ginsberg et. al., "IS-IS Prefix Attributes for Extended
IPv4 and IPv6 Reachability", IETF RFC 7794, March 2016
[SPRING-ISIS] Previdi el.al. "IS-IS Extensions for Segment Routing",
IETF work in progress, draft-ietf-isis-segment-routing-
extensions-06, December 2015
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8.2. Informative References
[IDSR] Filsfils et.al., "Segment Routing Architecture", IETF
work in progress, draft-ietf-spring-segment-routing-08,
May 2016
[ALLAN-1] Allan et.al., "A Framework for Computed Multicast applied
to MPLS based Segment Routing", draft-allan-spring-mpls-
mcast-framework-01, July 2016
9. Authors' Addresses
Dave Allan (editor)
Ericsson
300 Holger Way
San Jose, CA 95134
USA
Email: david.i.allan@ericsson.com
Uma Chunduri
Ericsson
300 Holger Way
San Jose, CA 95134
USA
Email: uma.chunduri@ericsson.com
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