Selection of Shortest Path Back to Source
By default, when a multicast packet is received on a PIM-capable interface in a multi-path
topology, the interface checks its IP routing table to determine the shortest path
back to the source.
If the alternate paths have the same cost, the first alternate path in the table
is picked as the path back to the source. For example, in the following example of
output from the
show ip route command, the first four routes have the same cost back to the source. However, 137.80.127.3
is chosen as the path to the source since it is the first one on the list. The device
rejects traffic from any port other than Port v11 on which 137.80.127.3 resides
Total number of IP routes: 19
Type Codes - B:BGP D:Connected I:ISIS S:Static R:RIP O:OSPF Cost - Dist/Metric
Destination Gateway Port Cost Type
..
172.17.41.4 137.80.127.3 v11 2 O
172.17.41.4 137.80.126.3 v10 2 O
172.17.41.4 137.80.129.1 v13 2 O
172.17.41.4 137.80.128.3 v12 2 O
172.17.41.8 0.0.0.0 1/2 1 D