3com S7906E Installationsanweisungen

 

1-4 

2)  As the source-side RP, RP 1 creates SA messages and periodically sends the SA messages to its 

MSDP peer. An SA message contains the source address (S), the multicast group address (G), 

and the address of the RP which has created this SA message (namely RP 1). 

3)  On MSDP peers, each SA message is subject to a reverse path forwarding (RPF) check and 

multicast policy–based filtering, so that only SA messages that have arrived along the correct path 

and passed the filtering are received and forwarded. This avoids delivery loops of SA messages. In 

addition, you can configure MSDP peers into an MSDP mesh group so as to avoid flooding of SA 

messages between MSDP peers.  

4)  SA messages are forwarded from one MSDP peer to another, and finally the information of the 

multicast source traverses all PIM-SM domains with MSDP peers (PIM-SM 2 and PIM-SM 3 in this 

example).  

5)  Upon receiving the SA message create by RP 1, RP 2 in PIM-SM 2 checks whether there are any 

receivers for the multicast group in the domain.  

z 

If so, the RPT for the multicast group G is maintained between RP 2 and the receivers. RP 2 

creates an (S, G) entry, and sends an (S, G) join message hop by hop towards DR 1 at the 

multicast source side, so that it can directly join the SPT rooted at the source over other PIM-SM 

domains. Then, the multicast data can flow along the SPT to RP 2 and is forwarded by RP 2 to the 

receivers along the RPT. Upon receiving the multicast traffic, the DR at the receiver side (DR 2) 

decides whether to initiate an RPT-to-SPT switchover process.  

z 

If no receivers for the group exist in the domain, RP 2 does not create an (S, G) entry and does join 

the SPT rooted at the source.  

 

z 

An MSDP mesh group refers to a group of MSDP peers that have MSDP peering relationships 

among one another and share the same group name.  

z 

When using MSDP for inter-domain multicasting, once an RP receives information form a multicast 

source, it no longer relies on RPs in other PIM-SM domains. The receivers can override the RPs in 

other domains and directly join the multicast source-based SPT.  

 

As shown in 

, there are five autonomous systems in the network, AS 1 through AS 5, with IGP 

enabled on routers within each AS and BGP or MBGP as the interoperation protocol among different 

ASs. Each AS contains at least one PIM-SM domain and each PIM-SM domain contains one ore more 

RPs. MSDP peering relationships have been established among different RPs. RP 3, RP 4 and RP 5 

are in an MSDP mesh group. On RP 7, RP 6 is configured as its static RPF peer.