User Guide    222
Configuring Layer 2 Multicast IGMP Snooping Configuration
Step 3 ip igmp snooping version {v1 | v2 | v3}
Configure the IGMP version.
v1:The switch works as an IGMPv1 Snooping switch. It can only process IGMPv1 report 
messages from the host. Report messages of other versions are ignored.
v2: The switch works as an IGMPv2 Snooping switch. It can process both IGMPv1 and IGMPv2 
report messages from the host. IGMPv3 report messages are ignored.
v3: The switch works as an IGMPv3 Snooping switch. It can process IGMPv1, IGMPv2 and 
IGMPv3 report messages from the host.
Step 4 ip igmp snooping drop-unknown
(Optional) Configure the way how the switch processes multicast streams that are sent to 
unknown multicast groups as Discard. By default, it is Forward.
Unknown multicast groups are multicast groups that do not match any of the groups 
announced in earlier IGMP membership reports, and thus cannot be found in the multicast 
forwarding table of the switch.
Note:
 IGMP Snooping and MLD Snooping share the setting of Unknown Multicast Groups, you 
need to ensure MLD Snooping is enabled globally. To enable MLD Snooping globally, use the 
ipv6 mld snooping command in global configuration mode.
Step 5 ip igmp snooping header-validation
(Optional) Enable header validation.
Generally, for IGMP packets, the TTL value should be 1, ToS field should be 0xC0, and Router 
Alert option should be 0x94040000. The fields validated depend on the IGMP version being 
used. IGMPv1 only checks the TTL field. IGMPv2 checks the TTL field and the Router Alert 
option. IGMPv3 checks TTL field, ToS field and Router Alert option. Packets that fail the 
validation process will be dropped.
Step 6 show ip igmp snooping
Show the basic IGMP Snooping configuration.
Step 7 end
Return to privileged EXEC mode.
Step 8 copy running-config startup-config
Save the settings in the configuration file.
The following example shows how to enable IGMP Snooping and header validation globally, 
and specify the IGMP Snooping version as IGMPv3, the way how the switch processes 
multicast streams that are sent to unknown multicast groups as discard. 
Switch#configure
Switch(config)#ip igmp snooping
Switch(config)#ip igmp snooping version v3
Switch(config)#ipv6 mld snooping
Switch(config)#ip igmp snooping drop-unknown
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