Internet Group Management Protocol
| Internet | IGMP | ||||
| IP ( IPv4 ) | |||||
| Network access | Ethernet |
Token bus |
Token ring |
FDDI | ... |
The Internet Group Management Protocol ( IGMP ) is a network protocol of the Internet protocol family and is used to organize multicast groups. Like ICMP, IGMP uses the Internet Protocol (IP) and is part of IP on all hosts that support the reception of IP multicasts.
use
The Internet Group Management Protocol is based on the Internet Protocol (IP) and enables IPv4 multicasting (group communication) on the Internet. IP multicasting is the distribution of IP packets under one IP address to several stations at the same time. IGMP offers the possibility to manage groups dynamically. Management does not take place in the sending station, but in the routers to which recipients of a multicast group are directly connected. IGMP offers functions with which a station informs a router that it wants to receive multicast IP packets from a specific multicast group. Multicast routing protocols ( DVMRP , MOSPF , PIM ) coordinate the transmission between the routers. The sender of multicast IP packets does not know which and how many stations are receiving their packets, because they only send a single data packet to their higher-level router. This duplicates the IP packet if necessary if it has several outgoing interfaces with receivers.
The Multicast Listener Discovery (MLD) integrated in ICMPv6 is used for IPv6 systems and works in a similar way to IGMP.
There are three versions of IGMP with the following basic properties:
- IGMPv1 A host can join a multicast group. Logging out is not implemented here. After a timeout , the host is discharged again.
- IGMPv2 A host can now log off from the multicast group (leave message implemented). This means that multicasts with a large bandwidth can also be handled.
- IGMPv3 You can now specify the source from which the multicast stream is required. This is an essential security aspect , although not the best one.
Packet format
IGMP packets (in version 1 and version 2) have a size of 64 bits. The following format is used:
| 0… 7 | 8… 15 | 16… 31 |
| Type | maximum response time | Checksum |
| Multicast group address | ||
The "maximum response time" field is only defined for type 0x11; this field is ignored for all other types.
The following values can be assumed for the type:
| Type | address | meaning |
|---|---|---|
| 0x11 | without | general request |
| 0x11 | With | group-specific request |
| 0x12 | With | Register / confirm IGMPv1 membership |
| 0x16 | With | Register / confirm IGMPv2 membership |
| 0x17 | With | End IGMPv2 membership |
| 0x22 | With | Register / confirm / terminate IGMPv3 membership |
Like ICMP , IGMP packets are encapsulated in IP datagrams and use the IP protocol number 2. IGMP is to be located in the OSI layer model in the network layer .