Multiple Auto-RP MA's

Hi all,
 
Finally back at the exam prep after a _long_ away period focusing on
everything else not lab prep related.
Currently brushing up on mcast again and have come across a behaviour I've
seen before, but haven't gotten to the bottom of.
 
When there are multiple MA's in an mcast domain, I'm seeing something
unexpected. Routers receiving autorp-discovery messages do not appear to
prefer one MA over another, regardless of MA's IP address. Rather, the
RP-mapping cache shows the contents of the most recently received discovery
message, and this is updated with every single autorp-discovery message
received.
 
(I'm sure I've read somewhere that all routers are "supposed" to prefer the
MA with the highest IP address).
Quick google search showed someone else has posted the question elsewhere,
but the answer given matches all other answers I seem to be able to find,
i.e. it dances around it without actually saying how a Cisco router chooses
a particular MA (or that it doesn't choose a particular MA).
 
So my theory, backed by labbing it up, is that routers populate their
RP-mapping cache with the most recently received autorp-discovery message,
and this flip-flops multiple times a minute (once for each MA in the
domain).
 
Just need a straight forward "yup, that's how it works" or "that's wrong,
this is how it works..." from the Brains-Trust to answer it once and for all
:)
 
Cheers,
Gavin

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Received on Mon Feb 14 2011 - 12:02:44 ART