Learn and verify IGMP snooping membership

IGMP snooping keeps track of the switch ports that have receivers for an IPv4 multicast group.

A Catalyst switch connects two Cisco routers on VLAN one hundred, with Protocol Independent Multicast and a rendezvous point already configured.

On the switch, verify that IGMP snooping is enabled for VLAN one hundred.

Before a receiver joins, this multicast group has no entry in the snooping table.

First, confirm ordinary connectivity between the routers with two successful unicast replies.

On the receiver interface, use the IGMP join-group command to join the selected multicast group.

The receiver now lists that group on its connected interface.

The switch lists the group in VLAN one hundred on the receiver-facing port.

On the source router, check that the receiver appears as a PIM neighbor across this switched network.

Send two pings to the multicast group and verify that the joined receiver answers.

Disable snooping for this VLAN to remove its snooped membership entries.

Multicast still works here because disabling snooping allows flooding; it does not block the group.

Re-enable snooping and verify that the receiver-facing membership appears again.

Join a second group on the same receiver to create an independent control.

The switch now lists both multicast groups on the receiver-facing port.

Remove the first join and verify that its switch entry disappears while the second group remains.

The withdrawn group no longer answers the multicast ping.

The second group still answers, confirming that the withdrawal affected only the selected group.

Ordinary unicast connectivity also remains intact.

This example uses configured receiver joins; check both membership and delivery when verifying multicast in your own lab.