MPLS and BGP RR

Unanswered Question
Nov 26th, 2007

Dear all

I was reading a document about MPLS VPN design in a carrier and find that it says :

Normally RRs are not required to enable MPLS, as they are not a transit point for any traffic, therefore MPLS need not be configured on them.

Is it correct ?

I have this problem too.
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pbenin Mon, 11/26/2007 - 06:59

BGP and MPBGP are required for VPN IP MPLS services.

The BGP architecture can be or not be based on RR.

It depends on the scalabilities requirements of the networks.

RR are not required for MPLS.

swaroop.potdar Mon, 11/26/2007 - 12:24

Pooria, yes thats true, BGP RR are a part of your control plane and never a part of the forwarding plane as a best practise.

Hence since there is no next-hop pointing towards the RR's ever for any prefixes learnt no label is ever required to reach till the RR.

But in a scneario where the RR is placed in the forwarding path then MPLS needs to be enabled on the RR. For eg:

PE1<-->P1<-->P2<-->RR1<-->P3<-->PE2

In the above hypothetical series connection scenario, the RR is in the forwarding path although it does only a control plane function. In this case it acts like a RR and also a P router, so MPLS needs to be enabled on the incoming and outgoing interfaces with LDP adjacencies.

But ideally, if a RR is used in a MPLS scenario then at maximum it needs to support VPNv4 address family only.

HTH-Cheers,

Swaroop

Harold Ritter Wed, 11/28/2007 - 10:17

Care should be taken with some vendors, which require routes to be resolvable via an LSP on the RR in order to consider the route as valid and therefore to reflect it.

This is not the case in IOS.

Regards,

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