Igmp Versions; Igmp Routing Example - Cisco ASR 9000 Series Configuration Manual

Internet Group Management Protocol
IGMP provides a means for hosts to indicate which multicast traffic they are interested in and for routers to
control and limit the flow of multicast traffic throughout the network. Routers build state by means of IGMP
and MLD messages; that is, router queries and host reports.
A set of queries and hosts that receive multicast data streams from the same source is called a multicast group.
Hosts use IGMP and MLD messages to join and leave multicast groups.
IGMP messages use group addresses, which are Class D IP addresses. The high-order four bits of a Class D
Note
address are 1110. Host group addresses can be in the range 224.0.0.0 to 239.255.255.255. The address
224.0.0.0 is guaranteed not to be assigned to any group. The address 224.0.0.1 is assigned to all systems
on a subnet. The address 224.0.0.2 is assigned to all routers on a subnet.

IGMP Versions

The following points describe IGMP versions 1, 2, and 3:
• IGMP Version 1 provides for the basic query-response mechanism that allows the multicast router to
determine which multicast groups are active and for other processes that enable hosts to join and leave
a multicast group.
• IGMP Version 2 extends IGMP allowing such features as the IGMP query timeout and the maximum
query-response time. See RFC 2236.
• IGMP Version 3 permits joins and leaves for certain source and group pairs instead of requesting traffic
from all sources in the multicast group.

IGMP Routing Example

Figure 2: IGMPv3 Signaling, on page 79
to group 239.1.1.1. The receiver wants to receive traffic addressed to group 239.1.1.1 from source 10.0.0.1
but not from source 10.0.1.1. The host must send an IGMPv3 message containing a list of sources and groups
(S, G) that it wants to join and a list of sources and groups (S, G) that it wants to leave. Router C can now use
this information to prune traffic from Source 10.0.1.1 so that only Source 10.0.0.1 traffic is being delivered
to
Cisco ASR 9000 Series Aggregation Services Router Multicast Configuration Guide, Release 6.0.x
78
Implementing Layer-3 Multicast Routing on Cisco IOS XR Software
illustrates two sources, 10.0.0.1 and 10.0.1.1, that are multicasting