Re: Multiple Auto-RP MA's

Hey Gavin, welcome back ;-)

How many mapping agents did you have? Each mapping agent does it's own
'best-rp- calculations and then announces this ...

The other thing that I noticed is that it can take a while for this fail
over to work. Auto-rp not the best choice if backup RPs are asked for.

I would think that a lab question that asked about primary and secondary
would probably be referring to BSR or perhaps anycast.

I would love to hear others thoughts as well. Have a good night, I am
signing off now ;-)

On Mon, Feb 14, 2011 at 7:02 AM, Gavin Schokman <g_schokman_at_yahoo.com.au>wrote:

> 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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