Reference Guide

580 | Multicast Source Discovery Protocol (MSDP)
www.dell.com | support.dell.com
3. When an MSDP peer receives an SA message, it determines if there are any group members within the
domain interested in any of the advertised sources. If there are, the receiving RP sends a join message
to the originating RP, creating an SPT to the source.
Figure 31-1. 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 31-2. 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.
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