IGMPv3 for PIM is backward compatible with IGMPv1/v2. According to RFC3376, the multicast router with IGMPv3 can use one of two methods to handle older query messages:
If an older version of IGMP is present on the router, the querier must use the lowest version of IGMP present on the network.
If a router that is not explicitly configured to use IGMPv1 or IGMPv2, detects an IGMPv1 query or IGMPv2 general query, it logs a rate-limited warning.
You can configure the IGMP version of an interface to version 3 regardless of the PIM or snooping mode.
You can configure whether the switch downgrades the version of IGMP to handle older query messages. If the switch downgrades, the host with IGMPv3 only capability does not work. If you do not configure the switch to downgrade the version of IGMP, the switch logs a warning.
Note
If you enable the explicit host tracking option on an IGMPv3 interface, you cannot downgrade to IGMPv1 or IGMPv2. You must disable explicit host tracking to downgrade the IGMP version.