11-2 CHAPTER 11: ADMINISTERING IP MULTICAST ROUTING
Enabling and
Disabling IGMP
The Internet Group Membership Protocol (IGMP) enables a router or
switch to determine whether group members exist in a subnetwork, or
leaf, of the Spanning Tree. The protocol uses two search methods to
make this determination:
■ Query mode — The router or switch with the lowest IP address in the
LAN broadcasts a query to all other members of the subnetwork to
determine whether they are also in the group. End stations respond to
the query with IGMP packets, which report the multicast group to
which they belong.
■ Snooping mode — A router or switch performs dynamic multicast
filtering based on IGMP snooping, which ensures that multicast
packets flood only to the appropriate ports within a routing interface.
When you select the IGMP option, the interface prompts you to enable or
disable IGMP snooping mode and IGMP query mode. Both are enabled
by default. Under most conditions, IGMP snooping mode and IGMP
query mode should remain enabled.
To enable or disable IGMP, from the top level of the Administration
Console, enter:
ip multicast igmp
The interface prompts you to enable or disable IGMP snooping and query
modes.
Example:
Enter IGMP snooping mode (disabled, enabled) [enabled]:
enabled
Enter IGMP query mode (disabled, enabled) [enabled]:
enabled
Top-Level Menu
system
ethernet
fddi
atm
bridge
➧ip
ipx
appletalk
snmp
analyzer
script
logout
interface
route
arp
atmArpServer
➧multicast
udpHelper
icmpRouterDiscovery
rip
ping
statistics
dvrmp
➧igmp
interface
tunnel
routeDisplay
cacheDisplay
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