IGMP Cheat Sheet
Overview
- IGMP (Internet Group Management Protocol) is used by hosts and adjacent routers on an IP network to establish multicast group memberships. It operates at the Network Layer (Layer 3) of the OSI model.
Common Uses
- Managing and controlling multicast groups in an IPv4 network.
IGMP Message Types
| IGMP Type | Description | Purpose |
|---|---|---|
| Membership Query | Message sent by routers to ask which multicast groups are joined by hosts. | Used to learn about group memberships. |
| Membership Report | Sent by hosts to report their multicast group memberships to routers. | Informs routers of the active memberships. |
| Leave Group | Informs routers that a host is leaving a multicast group. | Signals that the group should be maintained or closed if empty. |
IGMP Packet Structure
| Field | Size (bits) | Description |
|---|---|---|
| Type | 8 | Type of IGMP message (e.g., Query, Report) |
| Max Response Time | 8 | Time allowed before responding to a Query |
| Checksum | 16 | Error-checking field |
| Group Address | 32 | Address of the multicast group |
| Source Address | 32 | Address of the host sending the report (optional) |