Multicast RPF Failure


As one of the network engineers for a national Tennis organization you are responsible for all Multicast operations. Multicast is vital for the organization because video replays of all Tennis matches are being sent within the company. Without Multicast the network will be burdened by traffic overhead.


  • Configure OSPF on all routers, advertise all networks. Achieve full connectivity.
  • Configure dense-mode multicast only on routers LiveMatch,Ace, Alley and Backspin.
  • Configure router Backspin to join the multicast group on it’s FastEthernet interface.
  • Make sure you can ping the group address from router LiveMatch, you are not allowed to configure Multicast on router Backhand.




Multicast RPF Failure Network Topology

Video Solution:

Configuration Files

You need to register to download the GNS3 topology file. (Registration is free!)

Once you are logged in you will find the configuration files right here.

Opt In Image
Do you want your CCNA or CCNP Certificate?

The How to Master series helps you to understand complex topics like spanning-tree, VLANs, trunks, OSPF, EIGRP, BGP and more.

Written by René Molenaar - CCIE #41726

You May Also Like

About the Author: Rene Molenaar

René - CCIE #41726 is the creator of where he shares CCNA, CCNP and CCIE R&S labs. He also blogs about networking on


  1. Dear Rene,

    I`m just starting with multicast, and I have short question. About this task. We running Mcast thru LiveMatch,Ace, Alley and Backspin and RPF on Alley is failed because unicast part to S is via E0/0 not via Ser0/0 and packets are dropped.

    With mroute we can add static route and Incoming int will be changed from Null to Se0/0

    1. Hi Abedarev,

      There is one important lesson here to learn about multicast:

      With unicast routers are concerned where to deliver the packet to so they will do a lookup in the routing table for the destination IP address.

      Multicast is different, with multicast we are concerned where the source traffic is coming from. The router will do a lookup in the routing table to see if it can reach the source of the multicast stream on the interface where it is receiving the multicast stream from. If this is not the case we have a RPF failure.

      In this lab, Router Alley is receiving the multicast stream on its S0/0 interface but this is not the interface that it will use to reach (the source of the multicast). That’s why we have a RPF failure.

      RPF failures can be fixed by creating static mroutes.

  2. Superb lab, taught me a lot about troubleshooting Multicast.

    One in particular is to disable CEF and do a debug ip mpacket.

    Also if you do a "clear ip mroute * " you get a RPF fail message

    *Mar 1 01:08:02.331: IP(0): s= (FastEthernet1/0) d= id=1432, ttl=252, prot=1, len=114(100), RPF lookup failed for source

    The "show ip mroute count" command will list the RPF failure count too. Under the Other section, second field..

  3. Hi Rene,

    Do you think that it is a good option to modify the ospf cost on int f0/0 on router Backspin in order to reach the network for Alley instead of BackHand?

    Great lab!! congrats!

    1. It’s not a good option because you want to prefer a faster path (via ethernet) for your non-multicast traffic

Comments are closed.