User Guide

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Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E
78-14099-04
Chapter 21 Configuring IGMP Snooping
Enabling the IGMP Snooping Querier
Periodically, the IGMP querier sends IGMP queries that trigger IGMP report messages from the
switch that wants to receive IP multicast traffic.
IGMP snooping listens to these IGMP reports to establish appropriate forwarding. In a normal
network with IP multicast routing, the IP multicast router acts as the IGMP querier.
Note To enable IP multicast routing on the Catalyst 6500 series switches on a specific VLAN, enter
the ip pim sparse-mode command, the ip pim sparse-dense-mode command, or the ip pim
dense-mode command on that interface. See Chapter 18, “Configuring IP Multicast Layer 3
Switching” for more details.
• If the IP-multicast traffic in a VLAN needs to be Layer 2 switched only, an IP-multicast router is
not required, but without an IP-multicast router on a VLAN, you must configure another switch as
the IGMP querier so that it can send queries. You can use Cisco IOS commands to configure the
Catalyst 6500 series switches to generate such IGMP queries on a VLAN regardless of whether or
not IP multicast routing is enabled.
Restrictions
• IGMP snooping querier requires Release 12.1(8a)E and later.
• When configuring the IGMP snooping querier, configure the VLAN in the VLAN database or, with
Release 12.1(11b)E and later releases, configure the VLAN in global configuration mode (see
Chapter 9, “Configuring VLANs”).
• QoS does not support IGMP packets when IGMP snooping is enabled.
• You must configure an IP address on the VLAN interface for the IGMP snooping querier to start.
(See Chapter 12, “Configuring Layer 3 Interfaces”). When enabled, the IGMP snooping querier uses
the IP address as the query source address. The IGMP snooping querier disables itself if the IP
address is cleared and restarts when you configure an IP address.
Note With Release 12.1(11b)E and later, when you are in configuration mode you can enter EXEC mode-level
commands by entering the do keyword before the EXEC mode-level command.
Enabling the IGMP Snooping Querier
With Release 12.1(8a)E and later, use the IGMP snooping querier to support IGMP snooping in a VLAN
where PIM and IGMP are not configured because the multicast traffic does not need to be routed.
To enable the IGMP snooping querier in a VLAN, perform this task:
Command Purpose
Step 1
Router(config)# interface vlan vlan_ID
Selects the VLAN interface.
Step 2
Router(config-if)# ip igmp snooping querier
Enables the IGMP snooping querier.
Router(config-if)# no ip igmp snooping querier
Disables the IGMP snooping querier.