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How to achieve redundancy for multicast traffic



Redundancy for multicast traffic requires these two things:

  1. A unicast routing protocol, for example, Open Shortest Path First (OSPF) or Enhanced Interior Gateway Routing Protocol (EIGRP)
  2. Configuration of Protocol Independent Multicast (PIM) on all related layer 3 (L3) interfaces


PIM uses Reverse Path Forwarding (RPF) checks the unicast routing table to determine the proper paths for multicast data to traverse. If a unicast routing path changes, PIM relies upon the unicast routing protocol (OSPF) to properly converge. This helps the RPF checks of the PIM to show valid unicast paths to and from the IP address of the server that sources the multicast stream.

The unicast routing table is used to select paths for PIM. PIM uses RPF checks to ultimately determine the Shortest Path Tree (SPT) between the client (receiver VLAN) and the multicast source VLAN. So, the goal of PIM is the shortest unicast path between the receiver subnet and source subnet. As long as unicast routing protocol works as expected, and PIM is configured on all L3 links associated with the unicast routing protocol, nothing special needs to be configured for multicast to properly fail over.

For more detailed information on Multicast Traffic, refer to this document:

IP Multicast Best Practices for Enterprise Customers   [Multicast Enterprise]