Supporting%20IP%20Multicast%20over%20VPLS%20draft-serbest-l2vpn-vpls-mcast-03.txt

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Supporting IP Multicast over VPLSdraft-serbest-l2
vpn-vpls-mcast-03.txt

• Suresh Boddapati
• Venu Hemige
• Sunil Khandekar
• Vach Kompella
• Marc Lasserre
• Rob Nath
• Ray Qiu
• Yetik Serbest
• Himanshu Shah

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• Problem Definition
• In VPLS, multicast traffic is flooded to all
  sites, with or without receivers.
• Objectives
• Do not multicast send traffic to sites without
  receivers
• Keep core P routers stateless (Multicast)
• Reduce BW waste
• Use ingress replication, but replicate only to
  the sites with receivers.
• Should be extensible to use other tunneling
  technologies

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VPLS Multicast Procedures

• This draft addresses building of replication
  state on PEs for IGMP and PIM only.
• PEs on the customer facing ports (Downstream PEs)
  MUST perform IGMP/PIM snooping. There is no way
  around this.
• Procedures for IGMP snooping defined in
  draft-ietf-magma-snoop-12.txt
• This draft defines the procedures for PIM
  snooping.
• Snooping for various flavors of PIM are discussed
  in detail.
• This draft also defines the rules when both IGMP
  and PIM are active in a VPLS instance.
• PEs on Pseudo-Wire Ports (Upstream PEs) may learn
  multicast state using one of
• IGMP/PIM Snooping just like it is done on ACs.
• Via LDP (added in this revision).

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IGMP/PIM Snooping on PWs

• This requires no additional work. Work done for
  learning on ACs can be leveraged.
• Should be good for low to medium scale VPLS
  deployments.
• Since IGMP/PIM are soft-state protocols, the
  amount of periodic refreshes received on a PW is
  a function of
• f(numVplsInstances, numPEs, numGroups,
  numReceivers).
• In large-scale VPLS deployments, this will not
  scale very well.
• Proxy procedures can be implemented to mitigate
  the problem to a certain extent.
• But for a more robust solution, the WG
  recommended a reliable, refresh-free solution to
  build multicast states on PWs.

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Using LDP to learn multicast membership on PWs

• Why LDP?
• LDP is already being used in VPLS to setup PWs.
• LDP is a reliable protocol so refreshes of
  multicast states are not required.
• PIM Multicast States need only be built on the
  PE(s) connected to the downstream C-Routers and
  the upstream C-Router.
• PIM C-Join/Prunes need only be sent to the one
  upstream PE connected to the C-RPF-Neighbor -
  flooding is not required and is wasteful.

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Multicast State Learning via LDP

• PIM Hello TLV
• We define a new TLV to carry PIM C-Hellos that
  are snooped at the downstream PE to all remote
  PEs.
• This TLV is sent in an LDP Address Message to all
  remote PEs.
• Learning about PIM C-Routers is necessary for
• the PEs to determine where the upstream C-Router
  exists.
• to determine if Join Suppression is active in a
  VPLS instance.
• PIM Join TLV
• We define a new TLV to carry PIM C-Join/Prune
  messages that are snooped at the downstream PE to
  the upstream PE.
• This TLV is sent in an LDP Address Message to the
  upstream PE.
• PIM C-Packets must also be forwarded by the
  downstream PE (these are intended for C-routers).
• PIM C-Join/Prune packets may need to be
  unicast-forwarded to the C-RPF-Neighbor.

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Special Considerations

• Duplicate Traffic Scenarios
• There are several scenarios that can result in
  duplicate traffic.
• This draft defines how PEs should identify
  duplicate traffic and trigger PIM-Assert among
  the C-Routers.
• Why Unicast-Forward PIM C-Join/Prunes to the
  C-Upstream-Neighbor?
• For VPLS Multicast to work, PIM Join Suppression
  MUST be disabled on all C-Routers.
• Several of the existing PIM implementations do
  not support this ability to disable PIM Join
  Suppression.
• Whether C-Routers have this capability is out of
  the providers control.
• If a PE determines that PIM Join Suppression is
  active in a VPLS, then it SHOULD
  unicast-forward the C-Join/Prunes to prevent Join
  Suppression.
• PIM-BIDIR
• In this case, traffic may arrive on any
  interface, not just from the RPF.
• So PIM C-Join/Prunes need to be sent to all PEs
  via LDP.
• Forwarding State is built on all PEs.

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Next Steps

• Comments please.