file: /proc/sys/net/ipv4/force_igmp_version
variable: net.ipv4.force_igmp_version
Official reference

0 - (default) No enforcement of a IGMP version, IGMPv1/v2 fallback allowed. Will back to IGMPv3 mode again if all IGMPv1/v2 Querier Present timer expires. 1 - Enforce to use IGMP version 1. Will also reply IGMPv1 report if receive IGMPv2/v3 query. 2 - Enforce to use IGMP version 2. Will fallback to IGMPv1 if receive IGMPv1 query message. Will reply report if receive IGMPv3 query. 3 - Enforce to use IGMP version 3. The same react with default 0.

Note: this is not the same with force_mld_version because IGMPv3 RFC3376 Security Considerations does not have clear description that we could ignore other version messages completely as MLDv2 RFC3810. So make this value as default 0 is recommended.