Random multicast losses

[nathan.dixon]

Hi,

I have a large OSPF ring network carrying realtime multicast traffic. In the past we have had a number of services lost for no explained reason. Recently we have changed to OSPF from EIGRP and the number of lost services has increased. To fix the problem we have requested the stream at another point in the network and its come good at the faulty site. We have put this down to an RPF problem. There are 6 key sites each linked by an STM-1, each with 2 core routers (linked by a fast ethernet). We have also fixed the problem by breifly shutting down one STM-1 interface on a core router so as to force all of the traffic one-way around the ring. I know we can put an OSPF cost against an interface. Is this the only fix as we will have to do a lot of re-configuration as we are running about 10 VLAN's between each of the core site A and B routers. We dont want the ring traffic going through a VLAN so maybe we need to put costs onto these VLANs too (but keep them higher than a complete trip around the ring in the other direction).

Any comments welcome.

[mschooley]

a little confused about your topology, but it sound like you have 6 sites joined in a ring, with 2 routers at each site. Are you running pim dense or sparse, sparse would be recommended (sparse-dense actually), multiple rp's would be ok, trying to keep the rp as close to source as possible. Check rpf's make sure that the rpf is the correct interface. Lets say you have 2 core routers with 10 vlans a piece, and multicast is coming in on vlan10, he's going to do an rpf check the multicast out all the other multicast enabled interfaces, if there is an equal cost path back to there source, then he is going to pick the path with the largest ip address. If your rpf is not the interface that you think it should be, try using static mroute to set rpf interface to correct interface. Be careful because multicast static routes are looked at in there order that they are entered, like access list, and first one that matches is used.