Configuring per-port IGMP traffic filters


vlan <vid> ip igmp [auto < port-list > | blocked < port-list > | forward < port-list >]

Used in the VLAN context, specifies how each port handles IGMP traffic.

Default: auto.


Where a static multicast filter is configured on a port, and an IGMP filter created by this command applies to the same port, the IGMP filter overrides the static multicast filter for any inbound multicast traffic carrying the same multicast address as is configured in the static filter. See section "Filter Types and Operation" in the "Port Traffic Controls" chapter of the Management and Configuration Guide for your switch.


Suppose that you want to configure IGMP as follows for VLAN 1 on the 100/1000T ports on a module in slot 1:

Ports 1-2


Filter multicast traffic. Forward IGMP traffic to hosts on these ports that belong to the multicast group for which the traffic is intended. (Also forward any multicast traffic through any of these ports that is connected to a multicast router.)

Ports 3-4


Forward all multicast traffic through this port.

Ports 5-6


Drop all multicast traffic received from devices on these ports.

The different states of IGMP control traffic are auto, forward and blocked.


(Default) Causes the switch to interpret IGMP packets and to filter IP multicast traffic based on the IGMP packet information for ports belonging to a multicast group. This means that IGMP traffic will be forwarded on a specific port only if an IGMP host or multicast router is connected to the port.


Causes the switch to forward all IGMP and multicast transmissions through the port.


Causes the switch to drop all IGMP transmissions received from a specific port, and also blocks all outgoing IP Multicast packets for that port, thus preventing IGMP traffic from moving through specific ports.

For a description of the default behavior of data-driven switches, see Automatic fast-leave IGMP.

Depending on the privilege level, you could use one of the following commands to configure IGMP on VLAN 1 with the above settings:

switch(config)# vlan 1 ip igmp auto 1,2 
switch(config)# vlan 1 ip igmp forward 3,4
switch(config)# vlan 1 ip igmp blocked 5,6
switch(vlan-1)# ip igmp auto 1,2 
switch(vlan-1)# vlan 1 ip igmpforward 3,4
switch(vlan-1)# blocked 5,6

The following command displays the VLAN and per-port configuration resulting from the above commands.

switch> show igmp vlan 1 config