2-15
z One port can belong to only one multicast VLAN.
z The port connected to a user terminal must be a hybrid port.
z The multicast member ports must be in the same VLAN with the router port. Otherwise, the
multicast member port cannot receive multicast packets.
z If a router port is in a multicast VLAN, the router port must be configured as a trunk port or a hybrid
port that allows tagged packets to pass for the multicast VLAN. Otherwise, all the multicast
member ports in this multicast VLAN cannot receive multicast packets.
z When the multicast VLAN is set up, all IGMP report messages are forwarded to the router ports in
the multicast VLAN. If no router ports exist in the multicast VLAN, all IGMP report messages are
flooded within the multicast VLAN.
Displaying and Maintaining IGMP Snooping
After the configuration above, you can execute the following display commands in any view to verify
the configuration by checking the displayed information.
You can execute the reset command in user view to clear the statistics information about IGMP
Snooping.
Table 2-21 Display and maintain IGMP Snooping
Operation Command Remarks
Display the current IGMP
Snooping configuration
display igmp-snooping
configuration
Display IGMP Snooping
message statistics
display igmp-snooping
statistics
Display the information about
IP and MAC multicast groups in
one or all VLANs
display igmp-snooping
group [ vlan vlanid ]
You can execute the display
commands in any view.
Clear IGMP Snooping statistics
reset igmp-snooping
statistics
You can execute the reset
command in user view.
IGMP Snooping Configuration Examples
Configuring IGMP Snooping
Network requirements
To prevent multicast traffic from being flooded at Layer 2, enable IGMP snooping on Layer 2 switches.
z As shown in Figure 2-3, Router A connects to a multicast source (Source) through
GigabitEthernet1/0/2, and to Switch A through GigabitEthernet1/0/1.
z Run PIM-DM and IGMP on Router A. Run IGMP snooping on Switch A. Router A acts as the IGMP
querier.
z The multicast source sends multicast data to the multicast group 224.1.1.1. Host A and Host B are
receivers of the multicast group 224.1.1.1.
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