Tunneling is a common technique used with multicast technologies to traverse non- multicast capable networks. This greatly simplifies configuration, but it has the major drawback of “hiding” the real network topology and thus often prevents effective multicast replication. When configuring a tunnel, you have an option of enabling or disabling the IGP on the tunnel interface. If you plan to use the tunnel for multicast traffic delivery, it is necessary to enable PIM on the same interface. Because of the following two factors, you may easily encounter RPF failure issues:
- If no IGP is running on the tunnel, you must provide static mroutes to correct any RPF checks.
- If IGP is running on the tunnel interface, the cost of traversing the tunnel might be higher than the cost of traversing the underlying network. It is generally not a good idea to run the same IGP on the underlying network and on the tunnel. You may need to adjust metrics or provide static mroutes to correct any resulting problems.
R1(config)# ip multicast-routing distributed
R1(config)# ip prim rp-address 150.1.5.5
R1(config-if)# interface Tunnel59
R1(config-if)# ip unnumbered Loopback0
R1(config-if)# tunnel source Loopback0
R1(config-if)# tunnel destination 150.1.9.9
R1(config-if)# ip pim sparse-mode
R1(config-if)# exit
R1(config)# router ospf 100
R1(config-router)# passive-interface Tunnel59
R1(config-router)# exit