Working Group Dave Allan, Uma Chunduri
Internet Draft Ericsson
Intended status: Standards Track
Expires: December 2016
June 2016
OSPF extensions for Computed Multicast applied to MPLS based Segment
Routing
draft-allan-ospf-spring-multicast-00
Abstract
This document describes the OSPFv2 extensions required to support
multicast for MPLS based Segment Routing. In this approach OSPF
speakers compute their role in multicast tree construction based on
the information in the OSPF 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. Additional Router Information TLVs...........................4
4.1.1. SRM Compute Capability TLV.................................4
4.1.2. SRM SID Multicast Group Binding Sub-TLV....................4
4.1.3. SRM Pinned Tree Descriptor sub-TLV.........................5
5. Acknowledgements...............................................6
6. Security Considerations........................................6
7. IANA Considerations............................................7
8. References.....................................................7
8.1. Normative References.........................................7
8.2. Informative References.......................................7
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 three additional TLVs for OSPF to support the
segment routing multicast approach 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
The role of the IGP in the multicast architecture described in
[ALLAN-1] is to synchronize knowledge of the topology, knowledge of
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unicast SIDs, 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 IGP speakers. This
document specifies the TLVs necessary for OSPF version 2 to be the
IGP in said multicast architecture.
4. New TLVs
4.1. Additional Router Information TLVs
The following three TLV are in the Router Information Opaque LSA
specified in RFC 7770 for SRM compute capabilities and other TLVs in
OSPFv2 Extended Prefix Opaque LSA as specified in [RFC7684].
4.1.1. SRM Compute Capability TLV
The presence of this TLV in a router information LSA [RFC7770]
indicates both that the originating node supports computed spring
multicast, but also indicates the algorithm that is configured to be
used. All nodes supporting computed multicast are required to agree
on the algorithm for correct operation of the network.
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm OUI (24 bits) | Algorithm ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
The upper 24 bits contains an organizationally unique identifier (as
per RFC 7042) 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).
4.1.2. SRM SID Multicast Group Binding Sub-TLV
The SID Multicast Group Binding 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 sub-TLV does not have the T bit set, the SID TLV is not included
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in the message. This sub-TLV is part of OSPFv2 Extended Prefix TLV as
a sub-TLV from OSPFv2 Extended Prefix Opaque LSA as specified in
[RFC7684].
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 |
+-+-+-+-+-+-+-+-+ |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type = TBD (IANA assignment from OSPFv2 Extended Prefix TLV Sub-
TLVs Registry)
Length = octet size of the T/R, reserved fields, Group ID and the
SID sub-tlv information
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 ID: 4 octet IPv4 multicast address
SID sub-TLV = the segment ID to use for this source/group MDT. The
format is as per the SID/label sub-TLV defined in section 2.1 of
[SPRING-OSPF].
4.1.3. 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. This sub-TLV is part of
OSPFv2 Extended Prefix TLV as a sub-TLV from OSPFv2 Extended Prefix
Opaque LSA as specified in [RFC7684]. The encoding is an unstructured
list, where if the tree description exceeds the size, it may simply
use more than one sub-TLV.
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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-OSPF].
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.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| role descriptor 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| role descriptor 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| role descriptor 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| role descriptor n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
The encoding of a role descriptor is in the form:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Upstream Multicast SID sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unicast SID sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Multicast SID sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5. Acknowledgements
6. Security Considerations
For a future version of this document.
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7. IANA Considerations
This memo requires the assignment of 1 value from the OSPF Router
Information (RI) TLV registry:
- SRM Compute Capability TLV
This memo also requires the assignment of the following 2 Sub-TLV
values from the OSPFv2 Extended Prefix TLV Sub-TLV registry:
- SRM SID Multicast Group Binding sub-TLV
- SRM Pinned Tree Descriptor sub-TLV
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC7042] Eastlake, D. et. al.,"IANA Considerations and IETF
Protocol and Documentation Usage for IEEE 802
Parameters", IETF RFC 7042, October 2013
[RFC7684] Psenak et.al., "OSPFv2 Prefix/Link Attribute
Advertisement", IETF RFC 7684, November 2015
[RFC7770] Lindem et.al., "Extensions to OSPF for Advertising
Optional Router Capabilities", IETF RFC 7770, February
2016
[SPRING-OSPF] Psenak et.al., "OSPF Extensions for Segment Routing",
IETF work in progress, draft-ietf-ospf-segment-routing-
extensions-08, April 2016
8.2. Informative References
[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
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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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