Wednesday, December 23, 2009

Issues in 12.2S Inter-AS and CSC Multicast

Issues in 12.2S without Multicast VPN Inter-AS Support

Officially InterAS OptionB, optionC and CSC multicast are not supported on any code that doesn't have MDT SAFI support.

InterAS topology used for the below explanation –


  1. Option A – works

    1. does not require support for inter-AS MDTs. All works fine.

  2. Option B Inter-AS – doesn't work
the Source PE address is not shared between ASs

  1. 1st issue: PE1 (in AS1 connected to CE1) doesn't have its loopback IP address sent to the other AS (AS2). Only the loopback of ASBR1 is sent via eBGP to the other AS. Hence, P2 router on the other AS won't be able to perform successful RPF check for the PE1's loopback due to absence of routing info.
  2. 2nd issue: when PIM join in received from CE1 to PE1, PE1 will do a route lookup in the VRF routing table for the next-hop destination. This next-hop destination should be reachable via the MTI tunnel and there should be PIM neighborship with the next-hop. But since in Option2, the next-hop is changed by the ASBR to itself, there will be a contradiction and RPF check will fail on the PE.
  3. In an adjacent autonomous system, a PE router that wants to join a particular source of the default MDT for a given MVPN must know the originator's address of the source PE router. This presents some challenges for Option B inter-AS deployments because the originator next hop for VPNv4 routes is rewritten. The default MDT for inter-AS MVPN could not be established coz the P2 routers in other AS don't hold the PE1 routes.

  1. Option C Inter-AS - works

    1. In case of a typical deployment where RR contains all VPNv4 routes, it'll work. No issues. PE1-AS1 to PE2-AS2 MTI PIM neighborship should be up.

  2. CSC Hierarchical VPN multicast - works

    Check my blog for CSC multicast config (too much config to post here)–

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