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Understanding TCP/IP by Libor Dostálek, Alena Kabelová

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5.6 Internet Group Management Protocol

Like ICMP, IGMP is a service protocol for IP. IGMP packets are wrapped into IP datagrams. It is used for forwarding multicasts. Currently, version 2 of the IGMP protocol is up to date with RFC 2236 norms.

The following figure shows the structure of an IGMP version 2 packet:

5.6 Internet Group Management Protocol

Figure 5.30: IGMP v2 packet

The Type field acquires the values shown in the following table:

Value (hexadecimal)

Significance

11

IP Membership query ("Are there any members on the LAN?")

12

IGMPv1 Membership Report

16

IGMPv2 Membership Report

17

IGMPv2 Leave Group

The MRT (Maximum Response Time) field is only used in router requests ...

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