Configuring IP Multicast Routing

IP multicasting is a more efficient way to use network resources, especially for bandwidth-intensive services such as audio and video. IP multicast allows a host (source) to send packets to a group of hosts (receivers) anywhere within the IP network by using a special form of IP address called the IP multicast group address. The sending host inserts the multicast group address into the IP destination address field of the packet, and IP multicast routers and multilayer switches forward incoming IP multicast packets out all interfaces that lead to members of the multicast group.

Any host, whether it is a member of a group or not, can send to a group. However, only the members of a group receive the message. Membership in a multicast group is dynamic; hosts can join and leave at any time. There is no restriction on the location or number of members in a multicast group. A host can be a member of more than one multicast group at a time. How active a multicast group is and what members it has can vary from group to group and from time to time. A multicast group might be active for a long time, or it might be very short-lived. Membership in a group can change constantly. A group that has members might have no activity.

You must enable IP multicast routing, and configure the Protocol-Independent Multicast (PIM) version and PIM mode so that the IOS software can forward multicast packets and determine how the multilayer switch populates its multicast routing table. An interface can be configured to be in dense mode, sparse mode, or sparse-dense mode. The mode determines how the switch populates its multicast routing table and how it forwards multicast packets it receives from its directly connected LANs. You must enable PIM in one of these modes for an interface to perform IP multicast routing.

To enable and configure multicast routing on a multilayer switch, choose Device > IP Multicast Routing and use the IP Multicast Routing window. If you want to enable multicast routing with default configuration settings, choose Device > IP Multicast Wizard and use the IP Multicast Wizard.


Related Topics

Controlling Multicast Transmissions
"Configuring IP Multicast Routing," Catalyst 3550 Multilayer Switch Software Configuration Guide