Unanswered Question
Jan 29th, 2009

I have a switched network that is configured throughout using PIM sparse-dence-mode which is also configured for auto RP. There are a number of configured RP groups.

We would like to make sure any unauthorized multicast groups are unable to stream to the network by falling back to and using PIM dence-mode.

I see there is a command no dm-fallback, can I use this command to stop PIM from falling back to DM if there are no RP groups configured?

My concern is that auto RP initially uses PIM DM on start up to advertise the RP group information.

Will the no dm-command still allow the auto RP information to work in PIM DM or is there a better solution. I did read a long time ago about multicast sink holes but I can no longer seem to find out any information on this subject. Any ideas would be appreciated

I have this problem too.
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Giuseppe Larosa Thu, 01/29/2009 - 10:03

Hello Tim,

your concerns about the possibility of negative effects on auto-RP are present in the command reference notes:

A command that can help you to keep well-known auto RP multicast addresses treated as dense mode in a sparse mode network is:

ip pim autorp listener

To cause IP multicast traffic for the two Auto-RP groups and to be Protocol Independent Multicast (PIM) dense mode flooded across interfaces operating in PIM sparse mode, use the ip pim autorp listener command in global configuration mode. To disable this feature, use the no form of this command.

So an alternative could be to move to sparse mode +

ip pim autorp listener

I'm not sure if you need to add also

no ip pim dm-fallback

This should be tested

another alternative:

moving from auto-RP to boostrap protocol that uses hop by hop messages over and so is not affected by

no ip pim dm-fallback

BSR provides other advantages over auto-rp like redundancy and election of the BSR router while auto-rp can only have a manually configured mapping agent

Hope to help



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