Appendix A. IGMP Packet Formats

This appendix includes the packet formats from the specifications of the three versions of IGMP.

IGMP Version 3 Packet Formats

IGMPv3 is the result of the collective work of Brad Cain, Steve Deering, Bill Fenner, Isidor Kouvelas, and Ajit Thyagarajan. The packet formats are described in section 4 of the current specification. Here is section 4 from the specification in its entirety (it has been reformatted for consistency).

Message Formats

IGMP messages are encapsulated in IPv4 datagrams, with an IP protocol number of 2. Every IGMP message described in this document is sent with an IP Time-to-Live of 1 and carries an IP Router Alert option [RFC-2113] in its IP header.

There are two IGMP message types of concern to the ...

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