You can use the
Multicast Source Discovery Protocol (MSDP) to exchange multicast source
information between multiple Border Gateway Protocol (BGP) enabled Protocol
Independent Multicast (PIM) sparse-mode domains. In addition, MSDP can be used
to create an Anycast-RP configuration to provide RP redundancy and load
sharing. For information about BGP, see the
Cisco Nexus 9000
Series NX-OS Unicast Routing Configuration Guide.
When a receiver joins a group
that is transmitted by a source in another domain, the rendezvous point (RP)
sends PIM join messages in the direction of the source to build a shortest path
tree. The designated router (DR) sends packets on the sourcetree within the
source domain, which can travel through the RP in the source domain and along
the branches of the sourcetree to other domains. In domains where there are
receivers, RPs in those domains can be on the sourcetree. The peering
relationship is conducted over a TCP connection.
The following figure
shows four PIM domains. The connected RPs (routers) are called MSDP peers
because they are exchanging active source information with each other. Each
MSDP peer advertises its own set of multicast source information to the other
peers. Source Host 2 sends the multicast data to group 184.108.40.206. On RP 6, the
MSDP process learns about the source through PIM register messages and
generates Source-Active (SA) messages to its MSDP peers that contain
information about the sources in its domain. When RP 3 and RP 5 receive the SA
messages, they forward them to their MSDP peers. When RP 5 receives the request
from Host 1 for the multicast data on group 220.127.116.11, it builds a shortest
path tree to the source by sending a PIM join message in the direction of Host
2 at 18.104.22.168.
Figure 1. MSDP Peering Between RPs in
Different PIM Domains
When you configure MSDP
peering between each RP, you create a full mesh. Full MSDP meshing is typically
done within an autonomous system, as shown between RPs 1, 2, and 3, but not
across autonomous systems. You use BGP to do loop suppression and MSDP peer-RPF
to suppress looping SA messages.
You do not need to
configure BGP in order to use Anycast-RP (a set of RPs that can perform load
balancing and failover) within a PIM domain.
You can use PIM
Anycast (RFC 4610) to provide the Anycast-RP function instead of MSDP.
For detailed information
about MSDP, see