Where should I disabled multicast for Directly Connected Interfaces ?

Unanswered Question
Jun 25th, 2010


This follows on from a previous post which has now reached conclusion. However to optimise a multicast configuration I have deployed, I have read two conflicting documents from Cisco regarding where to disable multicast routing on directly connected Interfaces.

The official command reference for release 12.2SX onwards states :

Do not create directly connected subnets for the following cases:

  • To make more room available in the FIB TCAM
  • The switch is the first-hop router for a source
  • The entries are for Bidir, SSM, and DM mode groups

In these cases, if you enable the downloading of directly connected subnets, the directly connected source hits the MMLS (*,G) entry and is switched using the MMLS (*,G) entry. The registers are not sent to the route processor (in the case of PIM-SM), and the (S,G) state is not created on the first hop (in the case of PIM-DM).

However a best practice configuration guide for multicasting states:

If the switch is not the first hop router for any multicast sources, disable installation of directly connected

subnet entries:


no mls ip multicast connected

I have already disabled directly connected multicast on the Core switches on my backbone, because logically this doesn't directly host any multicast sources. However I would appreciate some clarification if this is indeed the correct way to do it, as the two documents cause confusion.

Thanks in advance.

I have this problem too.
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