Reference Guide

538 | Multicast Source Discovery Protocol (MSDP)
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Figure 28-1. Multicast Source Discovery Protocol
RPs advertise each (S,G) in its domain in Type, Length, Value (TLV) format. The total number of TLVs
contained in the SA is indicated in the “Entry Count” field. SA messages are transmitted every 60 seconds,
and immediately when a new source is detected.
Figure 28-2. MSDP SA Message Format
Anycast RP
Using Multicast Source Discovery Protocol (MSDP), Anycast RP provides load sharing and redundancy in
Protocol Independent Multicast sparse mode (PIM-SM) networks. Anycast RP allows two or more
rendezvous points (RPs) to share the load for source registration and the ability to act as hot backup routers
for each other.
Anycast RP allows two or more RPs to be configured with the same IP address on loopback interfaces. The
Anycast RP loopback address are configured with a 32-bit mask, making it a host address. All downstream
routers are configured to know that the Anycast RP loopback address is the IP address of their local RP. IP
routing automatically selects the closest RP for each source and receiver. Assuming that the sources are
AS X
AS Y
RP1
RP
R1
R2
R3
R4
1/1
1/21
2/11
3/21
3/41
4/31
4/1
1/2
PC 1
Receiver
PC 3
Receiver
2/1
PC 2
Source
O
S
P
F
Area 0
O
S
P
F
Area 0
+
P
I
M
+
I
G
M
P
+
P
I
M
+
I
G
M
P
M
S
D
P
P
e
e
r
s
h
i
p
B
G
P
Source Port
Seq. Number
Dest. Port
(639)
Type
Length
Entry Count
RP Address
MSDP 00
1
Reserved
Sprefix Length
(/32)
Group Address
Source Address
Code: 1: IPv4 Source-active
2: IPv4 Source-active Request
3: IPv4 Souce-active Response
4: Keepalive
5: Reserved
6: MSDP traceroute in progress
7: MSDP traceroute reply
Ack. Number
Offset
Reserved
Flags
Window
Checksum
Options Data
Urgent