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Duplicated packets in multicast network

I have a test network of 7 routers; 4 of them are connected over Frame Relay hub-and-spoke topology (using PtP links) and other links are serials and ethernets. I have enabled PIM sparse-dense mode on all interfaces and configured static rendez-vous point (with ip pim rp-address) on all routers. I have one server with 'ip igmp join' on loopback interface and test with ping. What happens, that ping from some routers provokes multiple responses:


Type escape sequence to abort.

Sending 1, 100-byte ICMP Echos to, timeout is 2 seconds:

Reply to request 0 from, 96 ms

Reply to request 0 from, 200 ms

Reply to request 0 from, 200 ms

Reply to request 0 from, 196 ms

Note the first packet having substantially shorter response time. This seems to happen when packets cross the FR part of the network. Anyone knows what could cause such duplicating of the packets? It seems that multicast packets get duplicated along their way to the receiver that then sends response to each duplicate it gets.

  • Other Network Infrastructure Subjects

Re: Duplicated packets in multicast network

It is better to use PIM - Sparse mode rather than PIM-Dense mode. And also instead of the command ip igmp join-group, you can use 'igmp static-group'.


Re: Duplicated packets in multicast network

borek -

Do you have the 'ip pim rp-address' command configured on the RP itself?