System information

Configuring IP Multicast Routing
8-17
For each attached network, a multicast router can be either a querier or a non-querier.
The querier router periodically sends general query messages to solicit group
membership information. Hosts on the network that are members of a multicast group
send report messages. When a host leaves a group, it sends a leave group message.
IP hosts use IGMP to report their group membership to directly connected multicast
routers. IGMP uses class D IP addresses for its group addresses that can range from
225.0.0.0 to 239.255.255.255.
The following multicast addressing rules apply to IGMP:
• The 224.0.0.0 IP address is guaranteed not to be assigned to any group.
• The address 224.0.0.1 is assigned to all systems on a subnetwork.
• The address 224.0.0.2 is assigned to all routers on a subnetwork.
Enabling IGMP
IGMP is enabled on all interfaces on which DVMRP or PIM is configured by default.
Controlling Access to IP Multicast Groups
The BSR learns about multicast group members that are connected to local networks
by sending IGMP host-query messages. The BSR then forwards all packets addressed
to the multicast group to these group members. IP multicast group access is
determined by associating the IGMP access group to an access list. Refer to Chapter 7
for more information on configuring access lists.
Follow these steps to configure to configure access for IP multicast groups:
1. Use the interface command in Global Configuration mode to enter the IGMP
interface, as shown below:
MOT(config-if)#interface {cable | ethernet | pos} <slot>/<interface>
where:
cable is the cable interface.
ethernet is the Ethernet interface.
pos is the Packet over SONET interface.