[c-nsp] Change VRF RD

[Peter Rathlev]

On Tue, 2009-09-08 at 16:05 -0700, Tony wrote:
> I'm curious, I thought setting the RD the same on each PE router
> (obviously per VPN) was the way to do things ?
...
> When do/should you set the RD to be different ? I'm guessing it's
> going to be for larger installations and to allow more customisation
> or something ?

The main difference (AFAIK) is that in a route reflector setup, your RR
will reflect all the different routes as long as all the PEs use
different RDs. This in turn means that each RR client (PE) will need
more memory to hold all possible prefixes, but on the other hand they
will be able to use one of the alternative paths immediately upon
discovering that the current best path is invalid, e.g. by the BGP next
hop for the current best path disappearing from the IGP.

With the same RD on all PEs your route reflector will only reflect the
current best path. When this invalidates you have to wait for the RR to
select a new best path and update the RR clients. In the mean time
traffic is black-holed.

So basically: Faster convergence in a route reflector setup.

-- 
Peter