3Com 5500-SI Configuration Manual page 589

Figure 172 Forwarding SA messages between MSDP peers
Source
RP1
AS1
As shown above, RP1 belongs to AS1. RP2, RP3 and RP4 belong to AS2. RP5 and RP6
belong to AS3. An MSDP peering relationship exists among these RPs. RP2, RP3, and
RP4 form a mesh group. These MSDP peers perform RPF check and process SA
messages forwarded to one another according to the following rules:
1 If an MSDP peer sending an SA message is an RP in the PIM-SM domain where the
multicast source resides (for example, when RP1 sends an SA message to RP2), the
receiver accepts the SA message and forwards the message to other peers.
2 If an RP has only one MSDP peer (for example, when RP2 sends an SA message to
RP1), the receiver accepts the SA message from the peer.
3 If an SA message comes from a static RPF peer (for example, when RP4 sends an SA
message to RP5), the receiver accepts the SA message and forwards it to other peers.
4 If an SA message comes from a peer that belongs to the same MSDP mesh group
with the receiver, the receiver accepts the SA message and forwards it to peers out of
the mesh group. For example, when RP2 sends an SA message to RP4, RP4 accepts
the message and forwards it to RP5 and RP6.
5 If an SA message comes from an MSDP peer in the same AS, and this peer is the next
hop on the optimal path to the RP in the PIM-SM domain where the multicast source
resides, the receiver accepts the SA message and forwards it to other peers. For
example, when RP4 sends an SA message to RP5, RP5 receives the message and
forwards it to RP6.
6 If an SA message comes from an MSDP peer in a different AS, and this AS is the next
AS of the RP optimal path in the PIM-SM domain where the multicast source resides
(for example, when RP4 sends an SA message to RP6), the receiver accepts the SA
message and forwards it to other peers.
7 The receiver does not accept or forward other SA messages.
Switch 5500 series switches do not support inter-domain routing. The RPF check rules
applies to the description in 5) only.
RP2
AS2
(4)
mesh group
(1)
(2)
RP3
MSDP peers
SA message
Introduction to MSDP 589
RP4
static peer
(6) (3)
(5)
RP5
AS3
RP6