Internet DRAFT - draft-xz-pim-flex-algo
draft-xz-pim-flex-algo
PIM B. Xu
Internet-Draft Z. Zhang
Intended status: Standards Track ZTE Corporation
Expires: 12 May 2023 8 November 2022
Flex-Algorithm TLV in PIM Join Attributes
draft-xz-pim-flex-algo-01
Abstract
This document defines a PIM join attribute to support building
multicast distribution trees flowing Flex-Algorithm path.
Status of This Memo
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This Internet-Draft will expire on 12 May 2023.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Flex-Algorithm Attribute . . . . . . . . . . . . . . . . . . 3
3.1. Flex-Algorithm Attribute Format . . . . . . . . . . . . . 3
3.2. Specification of the Flex-Algorithm Attribute . . . . . . 3
3.3. Use of the Flex-Algorithm Attribute . . . . . . . . . . . 4
3.3.1. Last-Hop Originate Flex-Algorithm Attribute . . . . . 4
3.3.2. Core Router Originate Flex-Algorithm Attribute . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Protocol Independent Multicast (PIM) get the upstream neighbor and
incoming interface to multicast source or Rendezvous Point (RP) from
the unicast routing protocol. As described in section 3 in
[RFC7761], PIM relies on an underlying topology-gathering protocol to
populate the MRIB (Multicast Routing Information Base). Usually the
MRIB is the best paths over the network based on the IGP metric. In
some case, PIM should choose a special path such as low latency path
or constraint-based path.
[I-D.ietf-lsr-flex-algo] specifies a set of extensions to IS-IS,
OSPFv2, and OSPFv3 to be used to compute the best paths along the
constrained topology.
In order to allow PIM build multicast distribution trees following
Flex-Algorithm topology, a PIM extension is needed. This document
defines a new join attributes to restrict the path of pim join.
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 [RFC2119].
2. Terminology
This document does not introduce more terminologies than [RFC7761],
[RFC5384], [RFC5496] and [I-D.ietf-lsr-flex-algo].
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3. Flex-Algorithm Attribute
[RFC5384] defines a pim Join Attributes are encoded as TLVs into the
Encoded-Source Address field of a PIM Join message. This document
specifies the Flex-Algorithm Attribute that allows the receiver to
select the Flex-Algorithm path.
3.1. Flex-Algorithm Attribute Format
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|E| Type=TBD | Length = 1 | Flex-Algo |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
F bit: The Transitive bit. Specifies whether the attribute is
transitive or non-transitive. This bit RECOMMENDED set to 1 and
the attribute will be transitived.
E bit: End-of-Attributes bit. Specifies whether this attribute is
the last. Set to zero if there are more attributes. Set to 1 if
this is the last attribute.
Type: TBD (To be assigned by IANA).
Length: 1-octet.
Flex-Algo: A 1-octet field Flex-Algorithm (see Section 4 of
[I-D.ietf-lsr-flex-algo]) to special the topology.
3.2. Specification of the Flex-Algorithm Attribute
The PIM router on the receiving side specifies the Flex-Algorithm of
the unicast route to the multicast source or RP according to the
local policy. It lookup unicast route in Flex-Algorithm topology,
and fills the specified Flex-Algorithm into the Flex-Algorithm
attribute when sending the join message to upstream neighbor.
After receiving join message with Flex-Algorithm attribute, the
upstream PIM router lookup unicast routes in the Flex-Algorithm
topology and selects the incoming interface and upstream neighbor.
And the continual join messages keep carrying the Flex-Algorithm
Attribute.
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When unicast routing is unreachable in the specific Flex-Algorithm
topology, there are two processing modes: Try-to-Forward and
Strictly-Topology. In Try-to-Forward mode, pim router continues to
search the unicast route without topology constrained, and the sent
join message will no longer carry Flex-Algorithm Attribute; In
Strictly-Topology mode, it is handled according to route unreachable.
If the Flex-Algorithm attribute of the same source address(or RP
address) and group address sent by multiple downstream PIM routers
are different, the join message from the neighbor, which has the
larger address, is selected.
If the Flex-Algo attribute is also received with the RPF vector
attribute([RFC5496]), the router MUST perform a lookup in the
corresponding Flexible Algorithm topology for the Encoded-Unicast
address from the vector attribute, and send a join along the
corresponding path defined by the Flex-Algo attribute, to the
upstream router.
There should be no more than one Flex-Algorithm attribute in a
Encoded-Source Address when PIM build a join message. If the PIM
router receives a join message with multiple Flex-Algorithm
attributes in a Encoded-Source Address, the first one is RECOMMENDED
be used.
3.3. Use of the Flex-Algorithm Attribute
3.3.1. Last-Hop Originate Flex-Algorithm Attribute
+----(gR2)------(gR4)----+
/ | | \
/ | | \
Source--(R1)(RP) | | (R6)--Recv
\ | | /
\ | | /
+----(rR3)------(rR5)----+
Figure 2
The network is divided into 2 planes by different Flex-Algorithm.
For example, R1/R2/R4/R6 belong to green plane, and R1/R3/R5/R6
belong to red plane. R1 is the source DR and R6 is last-hop DR. R6
is configured with policy rule1 to match (1.0.0.0/24, 233.252.0.1/32)
and set Flex-Algorithm M to select green plane, and R6 is configured
with policy rule2 to match (2.0.0.0/24, 233.252.0.2/32) and set Flex-
Algorithm N to select red plane. When JoinDesired(1.0.0.1,
233.252.0.1) ([RFC7761]) is TRUE, R6 will match policy rule1 in local
policy and send PIM join to R4 with Flex-Algorithm M in Flex-
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Algorithm Attribute. Also, when JoinDesired(2.0.0.1, 233.252.0.2) is
TRUE, R6 will match policy rule2 in local policy and send PIM join to
R5 with Flex-Algorithm N in Flex-Algorithm Attribute. The PIM
process for (*,G),(S,G) and (S,G,rpt) ([RFC7761]) is similar.
3.3.2. Core Router Originate Flex-Algorithm Attribute
+----(gR2)------(gR4)----+ +---(R7)--Recv
/ | | \ /
/ | | \ /
Source--(R1)(RP) | | (R6)
\ | | / \
\ | | / \
+----(rR3)------(rR5)----+ +---(R8)--Recv
Figure 3
The Flex-Algorithm policy can also be set on the core router. For
example, R6 is a core router and connect downstream routers R7/R8 in
Figure 3. If R7 sends PIM join with Flex-Algorithm M and R8 sends
PIM join with Flex-Algorithm N for a same PIM route, R6 SHOULD select
one from larger neighbor.
4. IANA Considerations
TBD.
5. Security Considerations
If PIM routers in the multicast tree select different Flex-Algorithm
topology based on different local policy, there may be a loop in the
network. The network administrator should be careful to set the
policies.
6. Acknowledgments
Would like to thank Sandy Breeze for his suggestions to this draft.
7. References
7.1. Normative References
[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", Work in Progress,
Internet-Draft, draft-ietf-lsr-flex-algo-26, 17 October
2022, <https://www.ietf.org/archive/id/draft-ietf-lsr-
flex-algo-26.txt>.
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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>.
[RFC5384] Boers, A., Wijnands, I., and E. Rosen, "The Protocol
Independent Multicast (PIM) Join Attribute Format",
RFC 5384, DOI 10.17487/RFC5384, November 2008,
<https://www.rfc-editor.org/info/rfc5384>.
[RFC5496] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path
Forwarding (RPF) Vector TLV", RFC 5496,
DOI 10.17487/RFC5496, March 2009,
<https://www.rfc-editor.org/info/rfc5496>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
Authors' Addresses
Benchong Xu
ZTE Corporation
China
Email: xu.benchong@zte.com.cn
Zheng Zhang
ZTE Corporation
China
Email: zhang.zheng@zte.com.cn
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