SA Message Processing
The following steps are taken by an MSDP peer whenever it processes an SA message:
1
Using the group address G of the (S, G) pair in the SA message, the peer locates the associated (*, G)
entry in the mroute table. If the (*, G) entry is found and its outgoing interface list is not null, then there
are active receivers in the PIM-SM domain for the source advertised in the SA message.
2
The MSDP peer then creates an (S, G) entry for the advertised source.
3
If the (S, G) entry did not already exist, the MSDP peer immediately triggers an (S, G) join toward the
source in order to join the source tree.
4
The peer then floods the SA message to all other MSDP peers with the exception of:
•
The MSDP peer from which the SA message was received.
•
Any MSDP peers that are in the same MSDP mesh group as this device (if the peer is a member of
a mesh group).
SA messages are stored locally in the device’s SA cache.
Note
MSDP Peers
Like BGP, MSDP establishes neighbor relationships with other MSDP peers. MSDP peers connect using TCP
port 639. The lower IP address peer takes the active role of opening the TCP connection. The higher IP address
peer waits in LISTEN state for the other to make the connection. MSDP peers send keepalive messages every
60 seconds. The arrival of data performs the same function as the keepalive message and keeps the session
from timing out. If no keepalive messages or data is received for 75 seconds, the TCP connection is reset.
Related Topics
Configuring an MSDP Peer, on page 184
Shutting Down an MSDP Peer, on page 186
Example: Configuring an MSDP Peer, on page 209
MSDP MD5 Password Authentication
The MSDP MD5 password authentication feature is an enhancement to support Message Digest 5 (MD5)
signature protection on a TCP connection between two MSDP peers. This feature provides added security by
protecting MSDP against the threat of spoofed TCP segments being introduced into the TCP connection
stream.
Related Topics
Configuring MSDP MD5 Password Authentication Between MSDP Peers, on page 187
Example: Configuring MSDP MD5 Password Authentication, on page 209
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3SE (Catalyst 3650 Switches)
OL-29890-01 177
Configuring MSDP
MSDP Peers
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