McDewey

Interoperability Between IGMPv1 and IGMPv2 With IGMPv1 and IGMPv2, only one router per IP subnet sends queries. This router is called the query router. In IGMPv1, the query router is chosen with the help of multicast routing protocol. In IGMPv2, it is chosen by the lowest IP address among the routers. Below are several possibilities: Scenario 1: IGMPv1 Router with a Mix of IGMPv1 and IGMPv2 Hosts The router does not understand the IGMPv2 report, and thus, all hosts must only use the IGMPv1 report. Scenario 2: IGMPv2 Router with a Mix of IGMPv2 and IGMPv3 Hosts IGMPv1 hosts do not understand the IGMPv2 query or the IGMPv2 group membership query. The router must only use IGMPv1, and suspend the leave operation. Scenario 3: IGMPv1 Router and IGMPv2 Router Located on the Same Segment The IGMPv1 router has no way to detect the IGMPv2 router. Therefore, the IGMPv2 router must be configured by the administrator as a IGMPv1 router. In any case, it possible that they do not agree on the query router. Interoperability Between IGMPv1/IGMPv2 and IGMPv3 With all versions of IGMP, only one router per IP subnet sends queries. This router is called the query router. In IGMPv1, the query router is chosen with the help of the multicast routing protocol. In IGMPv2 and IGMPv3, it is chosen by the lowest IP address among the routers. Below are several interoperability options. Scenario 1: IGMPv1/IGMPv2 Router with a Mix of IGMPv1/IGMPv2 and IGMPv3 Hosts Because the router does not understand the IGMPv3 reports, all hosts use the IGMPv1/IGMPv2 reports. Scenario 2: IGMPv3 Router with a Mix of IGMPv1/IGMPv2 and IGMPv3 Hosts The IGMPv1/IGMPv2 hosts do not understand the IGMPv3 query or IGMPv3 membership query. The router must only use the IGMP version that corresponds to the lowest IGMP client version present. If there are IGMPv3 and IGMPv2 clients, the router uses IGMPv2. If there are IGMPv1, IGMPv2, and IGMPv3 clients, the router uses IGMPv1. Scenario 3: Different Version Routers on the Same Segment When routers of different versions are present on the same segment, the lower-version routers have no means to detect the higher-version routers. Therefore, the different routers must be configured by the administrator as the same version. This version has to match the lowest version on any querying router present.