Huawei Quidway S3900 Series Operation Manual page 439

Operation Manual – Multicast Protocol
Quidway S3900 Series Ethernet Switches-Release 1510
5) If group members (namely, receivers) exists in the PIM-SM domains where MSDP
peers of RP1 reside, for example, if group members exist in the PIM-SM4 domain,
RP4 decapsulates the multicast data in the SA message and distributes the
multicast data to receivers along the RPT. RP4 also sends a Join message to the
multicast source S at the same time.
6) To avoid SA loop, MSDP peers perform RPF check on the received SA message.
After the RPF path is established, the data from the multicast source S is directly
sent to RP4 in the PIM-SM4 domain. Then RP4 forwards the data along the RPT
within the domain. Now the last-hop router of connected with group members in
the PIM-SM4 domain selects whether to switch to the SPT.
II. Forwarding messages between MSDP peers and performing RPF check
To establish an MSDP peering relationship between routers, you have to create routes
between routers to for SA messages to travel.
Assume that three autonomous systems (AS) exist. They are AS1, AS2, and AS3.
Each AS has a PIM-SM domain associated with it. Each PIM-SM domain contains at
least one RP. See Figure 8-4.
Source
Figure 8-4 Forwarding SA messages between MSDP peers
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.
(1)
(2)
RP1
AS1
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RP2
AS2
(4)
RP4
mesh group
(6)
RP3
RP6
MSDP peers
SA message
8-5
Chapter 8 MSDP Configuration
static peer
(3)
(5)
RP5
AS3