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Chapter 44
Configuring IP Multicast Routing
IGMP Snooping and CGMP Limitations
IGMPv3 uses new membership report messages that might not be correctly recognized by older IGMP
snooping switches.
For more information about switching issues related to IGMP (especially with CGMP), refer to the
"Understanding IGMP" section on page
State Maintenance Limitations
In PIM-SSM, the last hop router continues to periodically send (S, G) join messages if appropriate (S,
G) subscriptions are on the interfaces. Therefore, as long as receivers send (S, G) subscriptions, the
shortest path tree (SPT) state from the receivers to the source is maintained, even if the source does not
send traffic for longer periods of time (or even never).
This case is opposite to PIM-SM, where (S, G) state is maintained only if the source is sending traffic
and receivers are joining the group. If a source stops sending traffic for more than 3 minutes in PIM-SM,
the (S, G) state is deleted and only re-established after packets from the source arrive again through the
RPT. Because no mechanism in PIM-SSM notifies a receiver that a source is active, the network must
maintain the (S, G) state in PIM-SSM as long as receivers are requesting receipt of that channel.
Configuring SSM
Beginning in privileged EXEC mode, follow these steps to configure SSM:
Command
Step 1
ip pim ssm [default | range access-list]
Step 2
interface type number
Step 3
ip pim {sparse-mode | sparse-dense-mode}
Step 4
ip igmp version 3
Step 5
end
Step 6
show running-config
Step 7
copy running-config startup-config
Monitoring SSM
Beginning in privileged EXEC mode, follow these steps to monitor SSM.
Command
Router# show ip igmp groups detail
Router# show ip mroute
OL-12247-04
44-2.
Purpose
Define the SSM range of IP multicast addresses.
Select an interface that is connected to hosts on which
IGMPv3 can be enabled, and enter the interface configuration
mode.
Enable PIM on an interface. You must use either sparse mode
or sparse-dense mode.
Enable IGMPv3 on this interface. The default version of
IGMP is set to Version 2.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Purpose
Display the (S, G) channel subscription through IGMPv3.
Display whether a multicast group supports SSM service or
whether a source-specific host report was received.
Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
Configuring IP Multicast Routing
44-17
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