Versions: 00
PIM WG J. Asghar
Internet-Draft IJ. Wijnands
Intended status: Informational S. Krishnaswamy
Expires: April 15, 2013 Cisco Systems, Inc.
V. Arya
Directv, Inc.
October 15, 2012
Explicit RPF Vector
draft-asghar-pim-explicit-rpf-vector-00
Abstract
This document describes a use of the Reverse Path Forwarding (RPF)
Vector TLV as defined in [RPC 5496] to build multicast trees via an
explicitly configured path sent in the PIM join.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specification of Requirements . . . . . . . . . . . . . . . . . 3
3. Use of the Explicit RPF Vector . . . . . . . . . . . . . . . . 3
4. Explicit RPF Vector Attribute TLV Format . . . . . . . . . . . 4
5. Interoperability . . . . . . . . . . . . . . . . . . . . . . .4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . .4
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
9. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
In 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 stack 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 scenario's 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
vector(s) 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. 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. Use of the PIM Explicit RPF Vector
Normally PIM builds a receiver driven multicast forwarding tree
by sending PIM Joins from the leaf router towards root based on
unicast route lookup to source.
Figure 1 provides an example multicast join path R4->R3->R2->R1,
where the forwarding states are installed hop-by-hop dynamically.
<--- (S,G) Join ---
[S]---(R1)--(R2)---(R3)--(R4)---[R]
| |
| |
(R5)---(R6)
Figure 1
Figure 2 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 2
4. Explicit RPF Vector Attribute
This draft uses vector attribute 1 for specifying an explicit rpf
vector.
5. 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|S| Type | Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-.......
F bit
-----
Forward Unknown TLV. If this bit is set the TLV is forwarded
regardless of whether the router understands the Type. If the TLV
is known the F bit is ignored.
S bit
-----
Bottom of Stack. If this bit is set then this is the last
TLV in the stack.
Type
----
The Vector Attribute type is 1.
Length
------
Length depending on Address Family of Encoded-Unicast address.
Value
-----
Encoded-Unicast address.
6. Interoperability
The behaviour is dictated by the F flag as specified in RFC 5496.
7. IANA Considerations
An new attribute type from the "PIM Join Attribute Types" registry
needs to be assigned by IANA for the RPF Vector. The proposed
value is 1.
8. Security Considerations
Security of the RPF Vector Attribute is only guaranteed by the
security of the PIM packet, so the security considerations for PIM
join packets as described in PIM-SM [RFC4601] apply here.
9. Acknowledgments
The authors would like to thank Vatsa Kumar for the comments on
the draft.
10. 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.
[RFC5384] Boers, A., Wijnands, I., and E. Rosen, "The Protocol
Independent Multicast (PIM) Join Attribute Format",
RFC 5384, November 2008.
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
Vishal Arya
DIRECTV Inc.
2230 E Imperial Hwy
El Segundo, CA 90245
Email: varya@directv.com
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