Connectivity Guide
Advantages of PIM-SSM
Advantages of PIM-SSM include the following:
• PIM-SSM forwards multicast trac from a single source to a subnet. Other versions of PIM requires the receiver to subscribe to a
group. The receiver receives trac not just from the source that it is interested in, but from all the sources that send to that group.
PIM-SSM requires the receiver to specify the sources in which they are interested in to avoid receiving unnecessary trac.
• PIM-SSM is more ecient than PIM-SM because it immediately creates shortest path trees (SPT) to the source rather than using
shared trees. PIM-SM requires a shared tree rooted at the RP because IGMPv2 receivers do not express the source information in their
membership reports. Multicast trac passes from the source to the receiver through the RP, until the last hop router (LHR) learns the
source address, at which point it switches to the SPT.
PIM-SSM uses IGMPv3. Because receivers subscribe to a source and group, the RP and shared tree are unnecessary; only SPTs are
used. On OS10 systems, it is possible to use PIM-SM with IGMPv3 to achieve the same result, but PIM-SSM eliminates the
unnecessary protocol overhead.
Congure PIM-SSM
To congure a group range for PIM-SSM:
NOTE: The IP range, 232.0.0.0/8 is reserved for SSM. You do not have to explicitly congure this range.
1 Create an ACL rule to specify the range of addresses that should use SSM.
OS10# configure terminal
OS10(config)# ip access-list ssm-1
OS10(config-ipv4-acl)# permit ip any 236.0.0.0/8
OS10(config-ipv4-acl)# exit
2 Enable PIM-SSM for the range of addresses using the ip pim ssm-range command.
OS10(config)# ip pim ssm-range ssm-1
You can use the show ip pim ssm-range command to view the groups added in PIM-SSM conguration.
OS10# show ip pim ssm-range
Group Address / MaskLen
236.0.0.0 / 8
Expiry timers for S, G entries
You can congure expiry timers for S, G entries globally. The S, G entries expire in 210 seconds by default.
To congure the S, G expiry timer:
OS10# configure terminal
OS10(config)# ip pim sparse-mode sg-expiry-timer 500
Static rendezvous point
The rendezvous point (RP) is an interface on a router that acts as the root to a group-specic tree; every group must have an RP. You
must congure the RP on all nodes in your network.
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Multicast