IGMP snooping: packet walkthrough
IGMPv2 · VLAN 10 · group 239.1.1.1 · fast leave disabled
| Group | Receiver ports | Router port |
|---|---|---|
| 239.1.1.1 |
IGMP version differences
All versions let a switch learn multicast receiver ports. The walkthrough above uses IGMPv2.
| Behavior | v1 | v2 | v3 |
|---|---|---|---|
| Membership | Group G | Group G | Group G plus source INCLUDE/EXCLUDE lists |
| Report | 0x12 → G | 0x16 → G | 0x22 → 224.0.0.22 |
| Leave | Stop reporting; timeout | 0x17 → 224.0.0.2; query and timeout | State-change report; query and timer processing |
| Queries | General | General, group-specific | General, group-specific, group-and-source-specific |
Source-aware v3 snooping can forward different sources for the same group to different ports, if the switch supports it. Multicast data packet format does not change with the IGMP version.
Unknown-group forwarding, query scope, and fast-leave behavior depend on switch implementation and configuration.
References: IGMPv2 · IGMPv3 · Snooping recommendations