Multicast across BGP domains

Hello

Sometimes we may have multicast sources in one BGP domain and receivers in another BGP domain. In this case we need to exchange information across domains about:

  1. routes to get to the source of the multicast traffic
  2. sources of multicast traffic

 

To do 1), we need BGP to share multicast information, not just unicast.

To do 2), we need MSDP, a special TCP application that will inform domain B that domain A has a multicast source.

 

  1. To activate sharing RPF information, that is how to get to a source of multicast traffic, we need to activate a neighbor for a given address family, e.g.router bgp 100
    bgp log-neighbor-changes
    neighbor IBGP peer-group
    neighbor IBGP remote-as 100
    neighbor IBGP update-source Loopback0
    neighbor 150.1.3.3 peer-group IBGP
    neighbor 150.1.6.6 peer-group IBGP
    neighbor 150.1.9.9 peer-group IBGP
    !
    address-family ipv4
    neighbor IBGP route-reflector-client
    neighbor 150.1.3.3 activate
    neighbor 150.1.6.6 activate
    neighbor 150.1.9.9 activate
    exit-address-family
    !
    address-family ipv4 multicast
    neighbor IBGP route-reflector-client
    neighbor 150.1.3.3 activate
    neighbor 150.1.6.6 activate
    neighbor 150.1.9.9 activate
    exit-address-family
  2. We need to establish an MSDP peering on an RP in domain A with the RP in domain B, e.g.
    ip msdp peer 150.1.8.8 connect-source Loopback0 remote-as 200
    ip msdp peer 150.1.5.5 connect-source Loopback0 remote-as 200

Now we have everything we need to get multicast traffic from domain A to domain B. If a host in domain B joins a multicast stream, this info will go to its RP. In domain A, a source starts streaming. This goes to the RP in domain A. Domain A RP informs Domain B RP that it has a streaming source.

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