3com 8807 User Guide

C

HAPTER

 42: IGMP C

ONFIGURATION

In IGMP Version 1, hosts leave the multicast group quietly without informing the 
multicast router. In this case, the multicast router can only depend on the timeout 
of the response time of the multicast group to confirm that hosts leave the group. 
In Version 2, when a host is intended to leave, it will send a leave group message if 
it is the host who responds to the latest membership query message.

In IGMP Version 1, a query of a multicast router is targeted at all the multicast 
groups on the network segment, which is known as General Query.

In IGMP Version 2, Group-Specific Query is added besides general query. The 
destination IP address of the query packet is the IP address of the multicast group. 
The group address domain in the packet is also the IP address of the multicast 
group. This prevents the hosts of members of other multicast groups from sending 
response messages.

The Max Response Time is added in IGMP Version 2. It is used to dynamically 
adjust the allowed maximum time for a host to respond to the group query 
message.

For a large scale network with multicast routing protocol employed, many leaf 
networks may exist (a leaf network here refers to an end node of a multicast 
forwarding tree, it is a subnet that contains multicast clients only). It is a heavy 
load to configure and manage all these leaf networks.

You can ease the workload of configuring and managing leaf networks without 
affecting the multicast connections in them by enabling IGMP proxy on devices in 
these leaf networks.

After IGMP proxy is configured, the devices in leaf networks act as a host to the 
exterior network. They receive the multicast data of the associated group only 
when some of the hosts directly connected to them are multicast group members.