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:
- routes to get to the source of the multicast traffic
- 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.
- 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 - 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.