Computer Science 6390 – Advanced Computer Networks Dr. Jorge A. Cobb How to provide Inter-domain multicast routing? PIM-SM MSDP MBGP

2 PIM-SM Note that PIM-SM is a good candidate Receivers are usually sparsely located What we have seen thus far should work No need to do many changes for the Inter-domain We have only assumed a unicast “next-hop” However a single shared-tree is not desirable What if only one receiver, one sender (in same domain) and RP is many domains away? (expensive!) ASMs are no longer autonomous (depend on the AS of RP) Solution: one shared tree in each domain! Each domain has a RP

3 One RP per Domain Domain C Domain B Domain D Domain E Domain A r RP s

4 How to find each source The receiver joins the tree of its local RP as before Sources send data to their local RP Note: these two RP could be different! How can the RP at E (where receiver is) learn about the source at A? Use the Multicast Source Discovery Protocol (MSDP) MSDP runs in the RP at each domain When a new source joins the RP: MSDP informs all other domain RP’s of the new source in its domain

5 MSDP Peers Each MSDP router (i.e., each RP) maintains a TCP connection with the MSDP router (i.e. the RP) of each neighboring domain.

6 MSDP Peering Domain C Domain B Domain D Domain E Domain A MSDP Peers (TCP Session) RP

7 MSDP Flooding When the RP detects a new source in its domain, It sends a “source active” SA message to all its MSDP peers This message is flooded to all MSDP routers (i.e. to all RP’s) using the TCP sessions. How is the flooding done? Use a form of RPF, i.e., use the implicit broadcast tree of unicast If a RP receives a SA message from its next hop (next domain) to the source of the SA message, then it is accepted and send to all peers.

8 Broadcast tree of Domain A Domain C Domain B Domain D Domain E Unicast Path Domain A MSDP Peers RP

9 MSDP Steps Domain C Domain B Domain D Domain E SA Source Active Messages SA Domain A SA Message , MSDP Peers (TCP Session) RP s Register ,

10 Joining the SPT of the Source The RP at E, joins the SPT of the source (because it has at least one receiver) A join is sent along the path to the DR of the source This causes a path to be built in the SPT of S Also, the DR of the receiver may join the SPT of the source (if desired)

11 MSDP Overview Domain C Domain B Domain D Domain E Source Active Messages SA Domain A SA SA Message , r MSDP Peers (TCP Session) RP s Register , Join (*, ) Multicast Traffic Join (S, )

12 MSDP Overview Domain C Domain B Domain D Domain E Domain A RP r MSDP Peers Multicast Traffic RP s Join (S, )

13 Multiprotocol BGP Not all domains will support multicast Note that join messages are sent via unicast What if they traverse a domain where routers don’t support multicast? We need separate routing for regular unicast messages and multicast join messages MBGP is the same as BGP, except it provides more than one route MBGP may support many “protocols” Provide one route to the destination for each of these protocols E.g. “multicast” would be one “protocol”