One document matched: draft-ietf-pim-explicit-rpf-vector-03.txt
Differences from draft-ietf-pim-explicit-rpf-vector-02.txt
Versions: 03
PIM WG J. Asghar
Internet-Draft IJ. Wijnands
Intended status: Informational S. Krishnaswamy
Expires: April 17, 2014 A. Karan
Cisco Systems
V. Arya
Directv, Inc.
October 18, 2013
Explicit RPF Vector
draft-ietf-pim-explicit-rpf-vector-03
Abstract
This document defines a new Reverse Path Forwarding (RPF) Vector
TLV to build multicast trees via an explicit path sent in the PIM
join.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 17, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specification of Requirements . . . . . . . . . . . . . . . . . 3
3. Solution Requirements . . . . . . . . . . . . . . . . . . . . 3
4. Use of the Explicit RPF Vector . . . . . . . . . . . . . . . . 4
5. Explicit RPF Vector Attribute . . . . . . . . . . . . . . . . . 4
6. Mixed Vector Processing . . . . . . . . . . . . . . . . . . . . 4
7. Conflicting RPF Vectors . . . . . . . . . . . . . . . . . . . . 4
8. PIM Asserts . . . . . . . . . . . . . . . . . . . . . . . . . 4
9. Join Suppression. . . . . . . . . . . . . . . . . . . . . . . . 5
10. Vector Handling By Unsupported PIM Router . . . . . . . . . . 5
11. Explicit RPF Vector Attribute TLV Format . . . . . . . . . . 5
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
13. Security Considerations . . . . . . . . . . . . . . . . . . . 6
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
15. Normative References . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
For some applications, it might be useful to have a way to specify
the explicit path along which the PIM join is propagated.
This document defines a new TLV in the PIM Join Attribute message
[RFC5384] for specifying the explicit path.
The procedures in [RFC5496] define how a RPF vector can be used
to influence the path selection in the absence of a route to the
source. However, the same procedures can be used to override a
route to the source when it exists. It is possible to include
multiple RPF vectors in the list where each router along the
path will perform a unicast route lookup on the first vector in
the attribute list. Once the router owning the address of the RPF
vector is reached, following the procedures in [RFC5496], the RPF
vector will be removed from the attribute list. This will result
in a 'loosely' routed path based on the unicast reachability of
the RPF vector(s). We call this 'loosely' because we still depend
on unicast routing reachability to the RPF Vector.
In some scenarios we don't want to rely on the unicast reachability
to the RPF vector address and we want to build a path strictly
based on the RPF vectors. In that case the RPF vectors represent
a list of directly connected PIM neighbors along the path. For
these vectors we MUST NOT do a unicast route lookup. We call
these 'explicit' RPF vector addresses. If a router receiving an
Explicit RPF Vector does not have a PIM neighbor matching the
Explicit RPF Vector address it MUST NOT fall back to loosely
routing the join. Instead, it may process the packet and store
the RPF Vector list so that the PIM join may be sent out as soon
as the neighbor comes up. Since the behavior of the Explicit RPF
Vector differs from the loose RPF vector as defined [RFC5496],
we're defining a new attribute called the Explicit RPF Vector.
2. Specification of Requirements
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].
3. Solution Requirements
Some broadcast video transport networks use a multicast PIM
Live-Live resiliency model for video delivery based on PIM SSM
or PIM ASM. Live-Live implies using 2 active spatially diverse
multicast trees to transport video flows from root to leaf
multicast routers. The leaf multicast router receives 2 copies
from the PIM multicast core and will replicate 1 copy towards
the receivers [draft-mofrr-karan].
One of the requirements of the PIM Live-Live resiliency model
is to ensure path-diversity of the 2 active PIM trees in the
core such that they do not intersect to avoid a single point
of failure. IGP routed RPF paths of 2 PIM trees could be routed
over the same transit router and create a single point of failure.
It might be useful to have a way to specify the explicit path
along which the PIM join is propagated.
How the Explicit RPF Vector list is determined is outside the
scope of this document. It may either be manually configured by
the network operator or procedures may be implemented on the
egress router to dynamically calculate the vector list based on
a link state database protocol, like OSPF or IS-IS.
Due to the fact that the leaf router receives two copies of the
multicast stream via two diverse paths, there is no need for PIM
to repair the broken path immediately. It is up to the egress
router to either wait for the broken path to be repaired or build
a new explicit path using a new RPF vector list. Which method is
applied depends very much on how the vector list was determined
initially. Double failures are not considered and are outside the
scope of this document.
4. Use of the PIM Explicit RPF Vector
Figure 1 provides an example multicast join path
R4->R3->R6->R5->R2->R1, where the multicast join is explicitly
routed to the source hop-by-hop using the Explicit RPF Vector
list.
[S]---(R1)--(R2)---(R3)--(R4)---[R]
<--- | | ---
| | | |
| (R5)---(R6) |
- (S,G) Join -
Figure 1
5. Explicit RPF Vector Attribute
This draft uses PIM join attribute type 4 for specifying an Explicit
RPF Vector.
6. Mixed Vector Processing
Explicit RPF Vector attribute does not impact or restrict the
functionality of other RPF vector attributes in a PIM join. It is
possible to mix vectors of different types, such that some part of
the tree is explicit and other parts are loosely routed. RPF vectors
are processed in the order in which they are specified. That is, the
first RPF vector attribute is looked at and processed, it can be
either loose or explicit.
7. Conflicting RPF Vectors
It is possible that a PIM router has multiple downstream neighbors.
If for the same multicast route there is an inconsistency between the
Explicit RPF Vector lists provided by the downstream PIM neighbor,
the procedures as documented in section 3.3.3 [RFC5384] apply.
8. PIM Asserts
Section 3.3.3 of [RFC5496] specifies the procedures for how to deal
with PIM asserts when RPF vectors are used. The same procedures apply
to the Explicit RPF Vector. There is minor behavioral difference,
the route metric that is included in the PIM Assert should be the
route metric of the first Explicit RPF vector address in the list.
However, the first Explicit vector should always be directly connected,
so the Metric may likely be zero. The Metric will therefore not be a
tie breaker in the PIM Assert selection procedure.
9. Join Suppression
Section 3.3.4 of [RFC5496] specifies the procedures how to apply join
suppression when an RPF Vector attribute is included in the PIM join.
The same procedure applies to the Explicit RPF Vector attribute. The
procedure MUST match against all the Explicit RPF Vectors in the PIM
join before a PIM join can be suppressed.
10. Unsupported Explicit Vector Handling
The F bit MUST be set to 0 by a downstream router in the join that
is sent to the upstream router that does not support Explicit RPF
vector. See section 3.3.2 of [RFC5384]. Routers that don't support
the Explicit RPF Vector attribute MUST NOT forward the vector to
their upstream PIM neighbor and if required send a PIM join with
these attributes removed. This router will not be able to process
the Explicit Vector attribute from the list and cause a PIM control
plane routing loop with the upstream PIM neighbor.
11. Explicit RPF Vector Attribute 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|E| Type | Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-.......
F bit
-----
The F bit MUST be set to 0. Otherwise there could be loops.
E bit
-----
End of Attributes. If this bit is set then this is the last TLV
specified in the list.
Type
----
The Vector Attribute type is 4.
Length
------
Length depending on the Address Family of the Encoded-Unicast
address.
Value
-----
Encoded-Unicast address. This could be a valid primary or secondary
address.
12. IANA Considerations
A new attribute type from the "PIM Join Attribute Types" registry
needs to be assigned by IANA for the Explicit RPF Vector attribute.
The proposed value is 4.
13. Security Considerations
This document describes Explicit RPF Vector Attribute only which by
itself does not modify the security of PIM join packet or PIM-SM
operation and shares the security considerations described in
[RFC4601].
14. Acknowledgments
The authors would like to thank Vatsa Kumar and Nagendra Kumar for
the comments on the document.
15. Normative References
[RFC5496] Wijnands, IJ., Boers, A., Rosen, E., "The Reverse Path
Forwarding (RPF) Vector TLV", RFC 5496, March 2009.
[RFC5384] Boers, A., Wijnands, IJ., Rosen, E., "The Protocol
Independent Multicast (PIM) Join Attribute Format",
RFC 5384, Nov 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August
2006.
Authors' Addresses
Javed Asghar
Cisco Systems, Inc.
725, Alder Drive
Milpitas, CA 95035
Email: jasghar@cisco.com
IJsbrand Wijnands
Cisco Systems, Inc.
De kleetlaan 6a
Diegem 1831
Belgium
EMail: ice@cisco.com
Sowmya Krishnaswamy
Cisco Systems, Inc.
3750 Cisco Way
San Jose, CA 95134
EMail: sowkrish@cisco.com
Apoorva Karan
Cisco Systems, Inc.
3750 Cisco Way
San Jose, CA 95134
EMail: apoorva@cisco.com
Vishal Arya
DIRECTV Inc.
2230 E Imperial Hwy
El Segundo, CA 90245
Email: varya@directv.com
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