Configuration note for ip multicast multipath last updated 29/11/00 ----------------------------------------------------------------------------- Configuration Guide Load Split IP Multicast Traffic across Equal-Cost Paths If two or more equal-cost routes are available, unicast traffic will be load split between those paths. Multicast traffic for a (S,G) pair mode will always flow down from the RPF neighbor. According to the PIM protocols, this has to be the neighbor with the highest IP address for the case that there are more than one with the same metric (see RFC2362 for sparse mode). Thus, multicast traffic will by default never be load-split between multiple equal cost paths. Native load splitting To enable load-splitting between equal-cost paths configure the following command in global configuration mode: Command purpose ------------------------------------------------------------------------- ip multicast multipath Enable ip multicast load-splitting over equal-cost paths. With "ip multicast multipath", the RPF interface will be selected amongst equal cost paths depending on the source address. Multicast traffic from different sources will be load-split amongst the different equal cost paths. Note that this load-splitting is not load-balancing. Traffic from one source will always use one single path, even if that traffic far outweights traffic from other sources. If all the traffic to be load-split is from a single source but to different groups, then "ip multicast multipath" will have no effect, because load-splitting amongst different groups from the same source is not supported in this version. This command is currently also not supported for configurations in which a same PIM neighbor IP address is reachable via multiple equal cost paths. This typically happens if unnumbered interfaces are used, resulting in multiple interfaces on a router to carry the same IP address. Use different IP addresses for all interfaces, when configuring ip multicast multipath. Load splitting across tunnels. Load splitting for IP Multicast traffic can also be achieved by consolidating multiple parallel links into a single tunnel over which the multicast traffic is then routed. The methodology to use tunnels for load splitting is described in the IP Multicast configuration guides on CCO. Note that this methodology is more complex to set up and with the availability of the "ip multicast multipath" command tunnels typically only need to be used if per-packet load sharing is needed. ------------------------------------------------------------------------------ Commands reference ip multicast multipath To configure IP multicast load-splitting across multiple equal-cost paths, configure the "ip multicast multipath" global configuration command. ip multicast multipath no ip multicast multipath Defaults no ip multicast multicast In accordance with the PIM specifications, if multiple equal-cost paths exist, then the path from the PIM neighbor with the highest IP address is used. Command Modes Global configuration. Command History Release Modification --------------------------------- 12.0(7), 12.0(5)S, 12.0(8)T This command was introduced Usage Guidelines If this command is configured and multiple equal-cost paths towars a source exist, then the path choosen will be randomnly determined upon the source IP address. This will cause load splitting amongst the equal-cost paths between traffic from different sources but no load-splitting for traffic from the same source but to different groups. This command is currently not supported for configurations in which a same PIM neighbor IP address is reachable via multiple equal cost paths. This typically happens if unnumbered interfaces are used, resulting in multiple interfaces on a router to carry the same IP address. Use different IP addresses for all interfaces, when configuring ip multicast multipath. Related Commands Command Description ----------------------------------------------------------- show ip rpf Show the RPF interface for .