All things related to multicast

[Beau Williamson <>]

At 03:33 PM 2/6/2001, Havard Eidnes wrote:
>Sorry; must have forgotten to reply to that one.  I'm not sure
>how the router can revert to dense-mode behaviour with each and
>every interface configured for "ip pim sparse", though:
Havard,

Interface mode and group mode are not the same thing although they are 
related.  This is an often confused fact.  

The mode of a "group" depends on the existence of an RP for the group.  More 
specifically, the contents of the Group-to-RP mapping cache is the key here.  
(Hence the need for you to send the output of the 'show ip pim rp mapping' 
command.)  If there is an RP in the Group-to-RP mapping cache, then the 
router will assume that that group-range is to operate in Sparse mode and 
will create (*,G) state accordingly.

The *interface* mode of operation is a completely different matter.  In most 
cases, the interface mode (spares or dense) should match the mode of the 
group.  If you are using 'ip pim sparse-dense-mode' on an interface, the 
*interface* mode of operation AUTOMATICALLY follows the mode of the group.

So to summarize, it is the contents of the Group-to-RP mapping cache that 
actually controls the mode of the group.

Beau Williamson