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

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

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

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

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

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

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The receiver now lists that group on its connected interface.

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

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

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

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

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

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

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

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

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

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The withdrawn group no longer answers the multicast ping.

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

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Ordinary unicast connectivity also remains intact.

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