3Com Switch 7750 Configuration Guide

Configuring SA Message Transmission 491
among MSDP peers. For forwarded SA messages, you can also configure a
Time-to-Live (TTL) threshold to control the range where SA messages carrying
encapsulated data are transmitted.
To reduce the delay in obtaining the multicast source information, you can cache
SA messages on the router. The number of SA messages cached must not exceed
the system limit. The more messages are cached, the more router memory is
occupied. You need to determine the number of cached SA messages as required.
Configuration
Prerequisites
Before you configure SA message transmission, perform the following tasks:
■ Configuring a unicast routing protocol.
■ Configuring basic IP multicast functions.
■ Configuring basic PIM-SM functions.
■ Configuring basic MSDP functions.
Configuring the
Transmission and
Filtering of SA Request
Messages
After you configure to request SA messages from MSDP peers, when a router
receives a Join message, it sends an SA request message to the specified remote
MSDP peer, which responds with an SA message that it has cached. After sending
an SA request message, the router will get immediately a response from all active
multicast sources. By default, the router does not send any SA request message to
its MSDP peers upon receipt of a Join message; instead, it waits for the next SA
message.
The SA message that the remote MSDP peer responds with is cached in advance;
therefore, you must enable the SA message caching mechanism in advance.
Typically, only the routers caching SA messages can respond to SA request
messages.
After you have configured a rule for filtering received SA messages, if no ACL is
specified, all SA request messages sent by the corresponding MSDP peer will be
ignored; if an ACL is specified, the SA request messages that satisfy the ACL rule
are received while others are ignored.
Table 389 Configure the transmission and filtering of SA request messages
Operation Command Description
Enter system view system-view -
Enter MSDP view msdp -
Enable SA message
caching mechanism
cache-sa-enable Optional
By default, the router caches the
SA state upon receipt of an SA
message.
Configure to request SA
messages from an MSDP
peer
peer peer-address
request-sa-enable
Optional
By default, upon receipt of a Join
message, the router sends no SA
request message to its MSDP
peer but waits for the next SA
message.