Amer Networks SS3GR24i - Manual (Page 51)

SS3GR24i/SS3GR48i Layer3 Stackable Gigabit Switch User’s Guide
coordinate between multiple multicast routers that may be present
on a network by electing one of the multicast routers as the
‘querier’. This router then keeps track of the membership of
multicast groups that have active members on the network. IGMP
is used to determine whether the router should forward multicast
packets it receives to the subnetworks it is attached to or not. A
multicast router that has received a multicast packet will check to
determine if there is at least one member of a multicast group that
has requested to receive multicast packets from this source. If
there is one member, the packet is forwarded. If there are no
members, the packet is dropped.
IGMP Versions 1 and 2
Users that want to receive multicast packets need to be able to join
and leave multicast groups. This is accomplished using IGMP.
Figure 5-5. IGMP Message Format
The IGMP Type codes are shown below:
Type Meaning
0x11 Membership Query (if Group Address is 0.0.0.0)
0x11 Specific Group Membership Query (if Group Address is
Present)
0x16 Membership Report (version 2)
0x17 Leave a Group (version 2)
0x12 Membership Report (version 1)
Table 5-1. IGMP Type Codes
45