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Configuring Multicast Source Discovery Protocol
MSDP Configuration Task List
IPC-481
Cisco IOS IP Configuration Guide
Requesting Source Information from an MSDP Peer
Local RPs can send SA requests and get immediate response for all active sources for a given group. By
default, the router does not send any SA request messages to its MSDP peers when a new member joins
a group and wants to receive multicast traffic. The new member just waits to receive the next periodic
SA message.
If you want a new member of a group to learn the current, active multicast sources in a connected
PIM-SM domain that are sending to a group, configure the router to send SA request messages to the
specified MSDP peer when a new member joins a group. Doing so reduces join latency, but requires
some memory.
Note that information can be requested only from caching peers.
To configure this feature, use the following command in global configuration mode:
Repeat the preceding command for each MSDP peer that you want to supply you with SA messages.
An alternative to requesting source information is to cache the SA state, which is described in the section
“Caching SA State” earlier in this chapter. If you cache the information, you need not trigger a request
for it.
Controlling Source Information That Your Router Originates
There are two ways to control the multicast source information that originates with your router. You can
control the following:
• Which sources you will advertise (based on your sources)
• Whom you will provide source information to (based on knowing who is asking you for information)
To control which sources you will advertise, see the following section, “Redistributing Sources.” To
control whom you will provide source information to, see the section “Controlling Source Information
That Your Router Forwards” later in this chapter.
Redistributing Sources
SA messages are originated on RPs to which sources have registered. By default, any source that
registers with an RP will be advertised. The “A flag” is set in the RP when a source is registered. This
flag indicates that the source will be advertised in an SA unless it is filtered with the following command.
Command Purpose
Router(config)# ip msdp sa-request
{peer-address | peer-name}
Configures the router to send SA request messages to the specified
MSDP peer when a receiver becomes active, so the receiver can
learn about multicast sources in a group. The peer replies with the
information it is SA cache. If the peer does not have a cache
configured, this command provides nothing.