Reference Guide

Multicast sources in remote domains are stored on the RP in the source-active cache (SA cache). The system does not create
entries in the multicast routing table until there is a local receiver for the corresponding multicast group.
R3#show ip msdp peer
Peer Addr: 192.168.0.1
Local Addr: 192.168.0.3(639) Connect Source: Lo 0
State: Established Up/Down Time: 00:15:20
Timers: KeepAlive 30 sec, Hold time 75 sec
SourceActive packet count (in/out): 8/0
SAs learned from this peer: 1
SA Filtering:
Input (S,G) filter: none
Output (S,G) filter: none
Manage the Source-Active Cache
Each SA-originating RP caches the sources inside its domain (domain-local), and the sources which it has learned from its peers
(domain-remote).
By caching sources:
● domain-local receivers experience a lower join latency
● RPs can transmit SA messages periodically to prevent SA storms
● only sources that are in the cache are advertised in the SA to prevent transmitting multiple copies of the same source
information
Viewing the Source-Active Cache
To view the source-active cache, use the following command.
● View the SA cache.
EXEC Privilege mode
show ip msdp sa-cache
R3#show ip msdp sa-cache
MSDP Source-Active Cache - 1 entries
GroupAddr SourceAddr RPAddr LearnedFrom Expire UpTime
239.0.0.1 10.11.4.2 192.168.0.1 192.168.0.1 76 00:10:44
Limiting the Source-Active Cache
Set the upper limit of the number of active sources that the system caches.
The default active source limit is 500K messages. When the total number of active sources reaches the specified limit,
subsequent active sources are dropped even if they pass the reverse path forwarding (RPF) and policy check.
To limit the number of sources that SA cache stores, use the following command.
● Limit the number of sources that can be stored in the SA cache.
EXEC Privilege mode
show ip msdp sa-limit
If the total number of active sources is already larger than the limit when limiting is applied, the sources that are already in FTOS
are not discarded. To enforce the limit in such a situation, use the clear ip msdp sa-cache command to clear all existing
entries.
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Multicast Source Discovery Protocol (MSDP)