Interlogix NS3500-28T-4S User Manual - Manual (Page 167)

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Figure 4-7-5 IGMP Snooping Multicast Stream Control
IGMP Versions 1 and 2
Multicast groups allow members to join or leave at any time. IGMP provides the method for members and multicast
routers to communicate when joining or leaving a multicast group.
IGMP version 1 is defined in RFC 1112. It has a fixed packet size and no optional data.
The format of an IGMP packet is shown below:
IGMP Message Format
Octets
0 8 16 31
Type Response Time Checksum
Group Address (all zeros if this is a query)