Cisco Cisco IOS Software Release 12.0(19)S

This document describes the Explicit Tracking of Hosts, Groups, and Channels for IGMP Version 3 
feature in Cisco IOS Release 12.0(19)S. It includes the following sections:

The Internet Group Management Protocol (IGMP) is used by IP hosts to report their multicast group 
memberships to neighboring multicast routers. IGMP is available in versions 1, 2, and 3. IGMP 
Version 3 (IGMPv3) is supported in Cisco IOS Release 12.0(15)S, 12.1(5)T, 12.1(8)E, and later releases.

The Explicit Tracking of Hosts, Groups, and Channels for IGMP Version 3 feature enables a multicast 
router to explicitly track the membership of all multicast hosts in a particular multiaccess network. This 
enhancement to the Cisco IOS implementation of IGMPv3 enables the router to keep track of each 
individual host that is joined to a particular group or channel. The main benefits of this feature are that 
it provides minimal leave latencies, faster channel changing, and improved diagnostics capabilities for 
IGMP.

For more information on IGMPv3 and related features such as Source Specific Multicast (SSM), refer 
to the Cisco IOS IP Configuration Guide, Release 12.2.

12.0(19)S

This feature was introduced.