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Multicast RP Question

Level 1
Level 1


I'm having a problem with Multicast RPs(Rendez-vous points)

We are enabling multicast in our network and run PIM-SM between a few routers. One router has to be the RP. We configured a Loopback interface and configured all the routers to that ip address:

interface Loopback0
 description multicast rp
 ip address
 ip pim sparse-mode

ip pim rp-address

All the other routers show the RP as reachable:

client#sh ip pim rp
Group:, RP:, uptime 02:09:17, expires never

But not on the router on which the above Lo0 is configured:

rtr#sh ip pim rp
Group:, RP:, next RP-reachable in 00:00:11
Group:, RP:, next RP-reachable in 00:00:11

I don't understand why this router can't reach the RP. It is a local loopback interface, so it's always up and present in the routing table.

Does anyone have a clue?

Thanks & kind regards,


2 Replies 2

Level 1
Level 1

For multicast routing, there is this steps:

Router(config)# ip multicast-routing

In populating the multicast routing table, dense mode interfaces are always added to the table. Sparse mode interfaces are added to the table only when periodic join messages are received from downstream routers, or when a directly connected member is on the interface. When forwarding from a LAN, sparse mode operation occurs if an RP is known for the group. If so, the packets are encapsulated and sent toward the RP. When no RP is known, the packet is flooded in a dense mode fashion. If the multicast traffic from a specific source is sufficient, the first hop router of the receiver may send join messages toward the source to build a source-based distribution tree.

Router(config-if)# ip pim sparse-mode

Try this, and if this don't work allright, please put the ouput of this command 

show ip mroute

Level 10
Level 10


On the RP it will mostly show like this always as it not trying to reach a RP but it itself is 

this will be the case even if you have multicast traffic flowing across the router , something like this 

sh ip pim rp

Group:, RP:, next RP-reachable never  

Group:, RP:, next RP-reachable never    


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