Cisco Systems 78-11741-02 manual Messages to the specified IP address on a central router, IPC-441

Configuring IP Multicast Routing

Load Splitting IP Multicast Traffic Across Equal-Cost Paths Configuration Task List

Stub IP multicast routing allows stub sites to be configured quickly and easily for basic multicast connectivity, without the flooding of multicast packets and subsequent group pruning that occurs in dense mode, and without excessive administrative burden at the central site.

Before configuring stub IP multicast routing, you must have IP multicast routing configured on both the stub router and the central router. You must also have PIM dense mode configured on both the incoming and outgoing interfaces of the stub router.

Two steps are required to enable stub IP multicast routing. One task is performed on the stub router, and the other is performed on a central router one hop away from the stub router. By definition, a stub region is marked by a leaf router. That is, the stub router (leaf router) is the last stop before any hosts receiving multicast packets or the first stop for anyone sending multicast packets.

The first step is to configure the stub router to forward all IGMP host reports and leave messages received on the interface to an IP address. The reports are re-sent out the next hop interface toward the IP address, with the source address of that interface. This action enables a sort of “dense mode” join message, allowing stub sites not participating in PIM to indicate membership in multicast groups.

To configure the stub router to forward IGMP host reports and leave messages, use the following command in interface configuration mode. Specify the IP address of an interface on the central router. When the central router receives IGMP host report and leave messages, it appropriately adds or removes the interface from its outgoing list for that group.

Command	Purpose
Router(config-if)#ip igmp helper-address	On the stub router, forwards all IGMP host reports and leave
ip-address	messages to the specified IP address on a central router.

The second step is to configure an access list on the central router to filter all PIM control messages from the stub router. Thus, the central router does not by default add the stub router to its outgoing interface list for any multicast groups. This task has the side benefit of preventing a misconfigured PIM neighbor from participating in PIM.

To filter PIM control messages, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)#ip pim neighbor-filter	On the central router, filters all PIM control messages based on
access-list	the specified access list.

For an example of stub IP multicast routing, see the section “Stub IP Multicast Example” later in this chapter.

Load Splitting IP Multicast Traffic Across Equal-Cost Paths Configuration Task List

To configure load splitting of IP multicast traffic across equal-cost paths, perform the optional tasks described in either of the following sections:

•Enabling Native Load Splitting (Optional)

•Enabling Load Splitting Across Tunnels (Optional)

Cisco IOS IP Configuration Guide

IPC-441