Cisco Catalyst 3560-X Series, Software Configuration Manual

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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Configuring IP Multicast Routing
Configuring Optional Multicast Routing Features
Enabling CGMP Server Support
The switch serves as a CGMP server for devices that do not support IGMP snooping but have CGMP
client functionality. CGMP is a protocol used on Cisco routers and multilayer switches connected to
Layer 2 Catalyst switches to perform tasks similar to those performed by IGMP. CGMP is necessary
because the Layer 2 switch cannot distinguish between IP multicast data packets and IGMP report
messages, which are both at the MAC-level and are addressed to the same group address.
Beginning in privileged EXEC mode, follow these steps to enable the CGMP server on the switch
interface. This procedure is optional.
To disable CGMP on the interface, use the no ip cgmp interface configuration command.
When multiple Cisco CGMP-capable devices are connected to a switched network and the ip cgmp
proxy command is needed, we recommend that all devices be configured with the same CGMP option
and have precedence for becoming the IGMP querier over non-Cisco routers.
Command Purpose
Step 1 configure terminal Enter global configuration mode.
Step 2 interface interface-id Specify the interface that is connected to the Layer 2 Catalyst switch, and
enter interface configuration mode.
Step 3 ip cgmp [ proxy ] Enable CGMP on the interface.
By default, CGMP is disabled on all interfaces.
Enabling CGMP triggers a CGMP join message. Enable CGMP only on
Layer 3 interfaces connected to Layer 2 Catalyst switches.
(Optional) When you enter the proxy keyword, the CGMP proxy function
is enabled. The proxy router advertises the existence of
non-CGMP-capable routers by sending a CGMP join message with the
non-CGMP-capable router MAC address and a group address
of 0000.0000.0000.
Note To perform CGMP proxy, the switch must be the IGMP querier. If
you configure the
ip cgmp proxy command, you must manipulate
the IP addresses so that the switch is the IGMP querier, which
might be the highest or lowest IP address, depending on which
version of IGMP is running on the network. An IGMP Version 2
querier is selected based on the lowest IP address on the interface.
An IGMP Version 1 querier is selected based on the multicast
routing protocol used on the interface.
Step 4
end Return to privileged EXEC mode.
Step 5 show running-config Verify your entries.
Step 6 copy running-config startup-config (Optional) Save your entries in the configuration file.
Step 7 Verify the Layer 2 Catalyst switch CGMP-client configuration. For more
information, see the documentation that shipped with the product.