How can I prevent a multicast interface not to become member of the output interface list?

[Laszlo Zoltan]

There are two multicast routers receiving same multicast stream from two inbound links. The routers have to select one stream and to forward it to an output interface.

There is a problem if the router sends back the incoming stream to the other inbound interface (that is different from the stream has arrived) because of both routers are connected to same input networks. In this case multicast loop would be occurred.

Therefore, I need the interface to receive the multicast stream only.

Unfortunately, I could not find command to prohibit a multicast interface to become member of OIL explicitly.

I tried to filter IGMP messages from the input interface. It worked: No input interface in the OIL. But after deleting multicast routes no stream arrived from input interface. After removing IGMP filter from the input interface the streams have arrived. The interfaces are set to PIM-Sparse-Dense mode.

My questions:

How can I prevent a multicast interface not to become member of the output interface list?

Why does not arrive the input stream if I filter out IGMP on an interface?

Thanks,

Laszlo

[Peter Paluch]

Hi,

You have (probably inadvertently) posted this discussion four times; the other copies are here:

https://supportforums.cisco.com/discussion/12932671/how-can-i-prevent-multicast-interface-not-become-member-output-interface-list

https://supportforums.cisco.com/discussion/12932676/how-can-i-prevent-multicast-interface-not-become-member-output-interface-list

https://supportforums.cisco.com/discussion/12932681/how-can-i-prevent-multicast-interface-not-become-member-output-interface-list

Would you mind deleting them first?

Regarding your question: Both PIM-DM and PIM-SM have built-in mechanisms to prevent multicast routing loops from occurring. These are Designated Router elections (only PIM-SM) and the Assert mechanism. So I do not believe you should be worried about a particular interface joining the OIL as the multicast routing loops should not occur, anyway.

Are you seeing a different behavior? Could you perhaps post a picture of your topology showing where the multicast streams are entering your network, and the behavior you're concerned about?

Best regards,
Peter