Network Working Group Mike McBride
Internet Draft Cisco Systems
Intended Status: Informational
Expires: May 2008
November 2007
PIM Refresh Reduction Problem Statement
draft-mmcbride-pim-refresh-problem-statement-01
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Copyright (C) The IETF Trust (2007).
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Internet Draft PIM Refresh Problem Statement November 2007
Abstract
The PIM Working Group has a PIM refresh reduction charter goal. The
solution to this goal will help reduce the periodic join/prune
processing in PIM. The L3VPN Working Group identified this periodic
messaging of PIM as a potential scaling problem for PIM based MVPNs.
This document identifies the issues we are trying to solve with PIM
refresh reduction.
Table of Contents
1 Introduction ....................................... 2
2 History ............................................ 3
3 Problem ............................................ 3
4 Solutions .......................................... 4
5 Security Considerations ............................ 4
6 Iana Considerations ................................ 5
7 Acknowledgments .................................... 5
8 Normative References ............................... 5
9 Informative References ............................. 5
10 Authors' Addresses ................................. 5
11 Full Copyright Statement ........................... 6
12 Intellectual Property .............................. 6
1. Introduction
PIM Joins are refreshed every 60 seconds by a downstream router to
keep multicast state alive at the upstream router. With an increase
in state there is an increase in control traffic required for
refresh.
The PIM Working Group has a PIM refresh reduction charter goal. The
solution to this goal will help reduce the periodic join/prune
processing in PIM. The L3VPN Working Group identified this periodic
messaging of PIM as a potential scaling problem for PIM based MVPNs.
This document identifies the issues we are trying to solve with PIM
refresh reduction.
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Internet Draft PIM Refresh Problem Statement November 2007
2. History
At the November 2004 IETF, the L3VPN WG identified the effects of
periodic Join/Prune processing in PIM as a potential scalability
problem for PIM based MVPNs and asked that the PIM WG provide a
solution. The PIM WG subsequently created a pim refresh design team
to understand the problem area and provide a solution in needed.
Although there were disagreements on certain details, the design team
had rough agreement on a Join/Prune acknowledgement solution. But,
before recommending any solution, the PIM WG decided to ask the L3VPN
WG for a requirements (or similar) document to help determine if this
is really an area for which a solution is needed.
The PIM WG continued to discuss the future efforts we wanted to make
to PIM. The primary focus, of the working group, at the time was in
completing the PIMv2 [Fenner] draft. There are many enhancements we
could make to PIM. Do we refrain from future PIM enhancements and
close the working group? Or should we start going down the path of a
major PIMv3 revision?
The L3VPN did produce an MVPN requirements document [Morin] which did
help to better understand the future scalability requirements of
MVPN. But that requirements document didn't help in understanding at
what point PIM messaging could cause a scalability problem for PIM
based MVPNs.
In 2007, with the PIMv2 draft complete and the PIM WG tasked with a
new Charter, it was decided it would be of benefit for the WG to
provide enhancements to PIM. The WG has determined there is
additional work to be accomplished and is now chartered to
standardize extensions to RFC 4601 - Protocol Independent Multicast
Version 2 - Sparse Mode. These PIM extensions will include PIM
refresh reduction.
3. Problem
The PIM WG has decided to provide a solution(s) to reduce the effects
of the periodic Join/Prune processing in PIM. This solution could
help in the future scalability of PIM based MVPN as well as other PIM
deployments.
PIM Joins are refreshed every 60 seconds by a downstream router to
keep multicast state alive at the upstream router. With an increase
in multicast state there is an increase in PIM control traffic
required for refresh. Scaling could become an issue with MVPNs where,
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Internet Draft PIM Refresh Problem Statement November 2007
for instance, there could be 1000 MVPNs having 100 mroute entries
each along with 10 RPF neighbors. One million entries would then be
sent out on the MDT.
Additionally, route changes cause Joins to be sent to the new RPF
neighbor. If the Join is lost, there will be disruption of traffic.
There is no reliability in the Join/Prune exchange between downstream
and upstream routers. Larger values of holdtime in the Join/Prune PDU
would reduce the frequency of refreshes, but could also cause larger
convergence delays.
4. Solutions
This is not a solutions draft. Subsequent to this draft, there will
be drafts which outline solutions to this problem. The following
ideas have been discussed as possible solutions to be further
specified:
+ Join/Prune Ack extension to PIM.
+ Hard state (TCP) solution.
+ PIMv3 (strong RPF, explicit tracking, hard state, etc)
+ Include checksums in Hello messages rather than sending periodic
JPs.
+ Use long holdtimes.
5. Security Considerations
This document is a problem statement, which describes the reduction
of PIM messaging, and does not introduce security considerations by
itself. Any potential solution must protect against exploiting PIM
as specified in RFC 4601.
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6. Iana Considerations
This document does not require any action on the part of IANA.
7. Acknowledgments
We'd like to thank Dino Farinacci, Suresh Boddapati, Tom Pusateri,
Marshall Eubanks, Robert Kebler, Venu Hemige, Yiqun Cai, Yakov
Rekhter, Yetik Serbest, Albert Tian, for their work on the pim
refresh design team and helping the PIM WG to define a few possible
solutions.
8. Normative References
[Fenner] B. Fenner, "Protocol Independent Multicast - Sparse Mode
(PIM-SM)". RFC 4601
[MVPN] "Multicast in MPLS/BGP IP VPNs", Rosen, Aggarwal, July 2007,
draft-ietf-l3vpn-2547bis-mcast-05.txt
9. Informative References
[MORIN] T. Morin, "Requirements for Multicast in L3 Provider-
Provisioned VPNs", RFC 4834
10. Authors' Addresses
Mike McBride
mmcbride@cisco.com
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11. Full Copyright Statement
Copyright (C) The IETF Trust (2007).
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