IGMP Versions
- IGMPv1
- IGMPv2
- IGMPv3
IGMPv1 defines the group membership query and report processes. IGMPv2 extends IGMPv1 by adding the querier election and member leave mechanisms. IGMPv3 extends IGMPv2 by allowing hosts to specify the multicast sources they do or do not want to receive data from. IGMP versions are backward compatible. This means that a multicast router running a later IGMP version can identify IGMP messages sent from hosts running an earlier IGMP version, even though IGMP messages in different versions are sent using different formats.
All IGMP versions support the any-source multicast (ASM) model. IGMPv3 can be directly applied to the source-specific multicast (SSM) model. IGMPv1 and IGMPv2, however, can be applied to the SSM model only when IGMP SSM mapping is configured. For details about the ASM and SSM models, see Multicast Service Models.
Table 2-1 compares the three IGMP versions.
| Item | IGMPv1 | IGMPv2 | IGMPv3 |
|---|---|---|---|
| Querier election | Through Protocol Independent Multicast (PIM) | Through competition among multicast routers on a local network segment | Through competition among multicast routers on a local network segment |
| General Query message | Supported | Supported | Supported |
| Report message | Supported | Supported | Supported |
| Group-Specific Query message | Not supported | Supported | Supported |
| Leave message | Not supported | Supported | No specific Leave message is defined. Instead, group members send a specified type of Report message to notify multicast routers that they are leaving a group. |
| Group-and-Source-Specific Query message | Not supported | Not supported | Supported |
| Specifying multicast source in Report messages | Not supported | Not supported | Supported |
| Protocol message versions supported | IGMPv1 | IGMPv1, IGMPv2 | IGMPv1, IGMPv2, IGMPv3 |
| ASM model | Supported | Supported | Supported |
| SSM model | IGMP SSM mapping required | IGMP SSM mapping required | Supported |