IGMP and multicast support

The Cisco Nexus 3550-F Fusion (formerly ExaLINK Fusion) includes support for IGMP snooping to optimize delivery of IPv4 multicast traffic.

Enabling IGMP snooping

IGMP snooping is available on a per switch/mux object basis. IGMP snooping is disabled by default, but can be enabled using the igmp snooping command within the switch or mux configuration mode:

admin@N3550-F(config-switch:my_switch)> igmp snooping
Enabled IGMP snooping on switch "my_switch"

You may review your IGMP snooping settings via 'show igmp snooping', note that by default IGMP snooping is disabled (an error will display to reflect this):

admin@N3550-F(config-switch:my_switch)> show igmp snooping
IGMP snooping           : disabled
IGMP querier            : disabled
Multicast router ports  :
Flood unknown multicast : disabled
Fast leave              : disabled

Error: IGMP snooping not enabled

Once enabled, it can be disabled using the no form of the command:

admin@N3550-F(config-switch:my_switch)> no igmp snooping
Disabled IGMP snooping on switch "my_switch"

IGMP groups

Groups that object ports are subscribed to can be reviewed at any time via the 'show igmp groups' command:

admin@N3550-F(config-switch:my_switch)> show igmp groups
Group      Ports Version Timeout
---------- ----- ------- ------- B2    v2      259 C9    v3      63

IGMP querier

The Nexus 3550-F can also be configured as an IGMP querier to periodically send IGMP queries originating from a particular IP address. Use the igmp snooping querier command to enable IGMP querier functionality:

admin@N3550-F> configure switch my_switch igmp snooping querier
Configured IGMP querier on switch "my_switch" at address

The Nexus 3550-F will now periodically send IGMP queries from the designated address.

To disable the periodic sending of IGMP queries, use the no form of the command:

admin@N3550-F> configure switch my_switch no igmp snooping querier
Disabled IGMP querier on switch "my_switch"

Note: that the IGMP querier is enabled only if IGMP snooping is enabled.

IGMP Version

By default the Nexus 3550-F supports IGMPv3, however it can be configured to use IGMPv1 or IGMPv2. Use the igmp snooping version command to set this:

admin@N3550-F> configure switch my_switch igmp snooping version 2
Set IGMP version 2 on switch "my_switch"

Multicast router ports

For IGMP snooping to function correctly, the switch needs to know which ports are connected to multicast routers. A port can be configured to be a multicast router port by using the igmp mrouter command:

admin@N3550-F(config-switch:my_switch)> igmp mrouter A1
Configured port "A1" on switch "my_switch" as multicast router port

Multicast router ports can be removed by using the no form of the command:

admin@N3550-F(config-switch:my_switch)> no igmp mrouter A1
Removed port "A1" on switch "my_switch" as multicast router port

Unknown multicast groups

By default, all unknown multicast traffic will be suppressed on a switch or mux object. This behaviour can be changed using the igmp flood-unknown command.

admin@N3550-F(config-switch:my_switch)> igmp flood-unknown
Flooding unknown multicast traffic on switch "my_switch"

When this setting is enabled, traffic for a particular multicast group will be flooded before a host joins the group. Once a host joins the group, the group is no longer unknown and traffic will no longer be flooded for that group.

Use the no form of the igmp flood-unknown command to disable it:

admin@N3550-F(config-switch:my_switch)> no igmp flood-unknown
Suppressing unknown multicast traffic on switch "my_switch"

IGMP fast leave

IGMP snooping on the Nexus 3550-F supports "fast leave" functionality to reduce the time it takes for a host to leave a multicast group. When fast leave is enabled, a port is immediately removed from a multicast group when a IGMPv2 Leave message is received on the port.


At most one host can be connected to each non-router port when fast leave is enabled.

Ports with more than one host connected may be incorrectly dropped from multicast groups.

Use the command igmp snooping fast-leave to enable fast leave mode, and the no form of this command to disable fast leave mode.

admin@N3550-F(config-switch:my_switch)> igmp snooping fast-leave
Enabling IGMP fast leave mode on switch "my_switch"

admin@N3550-F(config-switch:my_switch)> no igmp snooping fast-leave
Disabling IGMP fast leave mode on switch "my_switch"

Manually setting multicast filters

It is possible to manually add multicast filters instead of/as well as using IGMP snooping:

admin@N3550-F(config-switch:my_switch)> igmp static-group port B1
Added static multicast group "" for port "B1" on switch "my_switch"

This page was last updated on Feb-19-2021.