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Configuring IP Multicast Routing
Load Splitting IP Multicast Traffic Across Equal-Cost Paths Configuration Task List
IPC-442
Cisco IOS IP Configuration Guide
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:
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
Command Purpose
Router(config)# ip multicast multipath
Enables load splitting of IP multicast traffic across multiple
equal-cost paths.
Router A Router B
Source
S1
E0
S0
Multicast
member
Two multicast
equal-cost links
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