Cisco Systems 78-11741-02 Enabling Native Load Splitting, Enabling Load Splitting Across Tunnels

Configuring IP Multicast Routing

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

Enabling Native Load Splitting

If two or more equal-cost paths from a source are available, unicast traffic will be load split across those paths. However, by default multicast traffic will not be load split across multiple equal-cost paths. In general, multicast traffic will flow down from the RPF neighbor. According to PIM specifications, this neighbor must have the highest IP address if more than one neighbor has the same metric (refer to RFC 2362 for PIM sparse mode information).

To enable load splitting of IP multicast traffic across multiple equal-cost paths, use the following command in global configuration mode:

Command	Purpose
Router(config)# ip multicast multipath	Enables load splitting of IP multicast traffic across multiple
	equal-cost paths.

When the ip multicast multipath global configuration command is configured and multiple equal-cost paths exist, the path in which multicast traffic will travel is selected based on the source IP address. Multicast traffic from different sources will be load split across the different equal-cost paths. Load splitting will not occur across equal-cost paths for multicast traffic from the same source sent to different multicast groups.

Note The ip multicast multipath global configuration command load splits the traffic and does not load balance the traffic. Traffic from a source will use only one path, even if the traffic far outweighs traffic from other sources.

The ip multicast multipath command does not support configurations in which the same PIM neighbor IP address is reachable through multiple equal-cost paths. This situation typically occurs if unnumbered interfaces are used. We recommend using different IP addresses for all interfaces when configuring the ip multicast multipath command.

Enabling Load Splitting Across Tunnels

Load splitting of IP multicast traffic can be achieved by consolidating multiple parallel links into a single tunnel over which the multicast traffic is then routed. Figure 72 shows an example of a topology in which this method can be used. Router A and Router B are connected with two equal-cost links.

Figure 72 Two Multicast Links Without Load Splitting

		Two multicast
		equal-cost links
	Router A	S0	Router B
E0
		S1

43281

Source	Multicast
	member

Cisco IOS IP Configuration Guide

IPC-442