User's Manual

48-20
4. At the same time, the source RP in the domain, generates a SA – Source Active message, and send it
to the MSDP entity – RP2.
5. If there’s another member in the same domain with the MSDP entity which is named as RP3, RP3 will
distribute the multicast datagram encapsulated in the SA messages to the members of the shared tree,
and send join messages to the multicast source. That means RP creates an entry (S, G), and send join
messages for (S, G) hop by hop, so that (S, G) can reach the SPT which takes the multicast source as
the root across the PIM-SM domain.
If there no members in the same domain with MSDP entity – RP2, RP2 will not create the (S, G) entry
nor it will join the SPT which takes the multicast source as the root.
6. When the reverse route has been set up, the multicast datagram from the source will be directly
delivered to RP3, and RP will forward the datagram to the shared tree. At this time, the router which is
closest to the domain members can determine itself whether or not to switch to SPT.
Figure 48-3 Network Topology for MSDP Entry
Configuration tasks are listed as below:
Prerequisites:
Enable the single cast routing protocol and PIM protocol on every router, and make sure that the inter-domain
routing works well and multicasting inside the domain works well.
Suppose the multicast server S in Domain A offers multicast programs at 224.1.1.1. A host in Domain C
named R subscribes this program. Before MSDP is configured C cannot subscribe the multicast program.
However, with the following configuration, R is able to receive programs offered by S.
RP1 in Domain A:
Switch#config
Switch(config)#interface vlan 1
Switch(Config-if-Vlan1)#ip address 10.1.1.1 255.255.255.0
Switch(Config-if-Vlan1)#exit
Switch(config)#router msdp
Switch(router-msdp)#peer 10.1.1.2
DomainA
RP1
DomainB
RP2
RouterA
RouterB
DomainC
RP3
Source
Receiver