Re: MPLS VPN doubt

Yes, you can use two different rd for the same vrf. The purpose of the rd
is to make the route unique in the provider backbone. Once the 64 bit rd is
added to the 32 bit ipv4 prefix, you have a unique 96 bit vpnv4 prefix.

Now if you have the same customer vpn prefix at two different PE routers
(redundant paths) and the RD's are the same, the prefix looks identical on
the backbone. Now asume the provider is using route reflectors to scale bgp
on the backbone. The RR will decide the best path each prefix and send only
that best path info to the RR clients.

So even though you sold your customer redundant paths to a site, some of
your edge routers don't see the second path because of the RR. Now if the
link to the prefix you have fails, you have an outage from those RR client
sites until BGP converges and the RR sends you the second path.

To get the RR to send both paths to the clients is not possible because RR
only send the best path for each prefix, so you need to make the prefixes
unique. By changing the RD at one PE, both prefixes become unique 96 bit
prefixes and the RR now sees two unique routes and sends both to the
clients.

The route targets are responsible for importing routes into the vrf, so you
keep those the same.

Many providers that I have worked on use a rd format pe#: vpn# so that
routes are always unique.
 On Jun 30, 2011 4:13 AM, "HEMANTH RAJ" <hemanthrj_at_gmail.com> wrote:
> Hi fellows
> I have a doubt regarding MPLS L3 VPN, Can we use two different RD's in the
> same VRF. Is it possible. In MPLS Fundamentals, I came across a sentence
> which says that two different RD's are possible for the same VRF.
> Can anyone shed some light on it.
>
>
>
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Received on Thu Jun 30 2011 - 08:44:47 ART