Subject: Doubt in BGP for L3 VPNs

From: John Smith <[email-masked]>
Date: Thu, 14 Apr 2005 01:18:06 +0100 (BST)

Hi,

PEx -- PEz -- PEy

This is in the context of L3 VPNs. PEz is a BGP route reflector connected to two clients
PEx and PEy (its also connected to other PE routers which i have omitted for the sake of
clarity).

By default, PEy recieves all BGP UPDATEs from PEx which have PEx as the NEXT_HOP. This
happens for the NEXT_HOP attribute in the BGP UPDATE message and also for the next-hop
that is encoded inside MP_REACH_NLRI. This way, PEy knows that it needs to put an outer
label that corresponds to the router PEx.

Now, we want all the BGP labelled packets to terminate at the RR viz PEz. So, we
configured next-hop-self on the RR thinking that it will change the NEXT_HOP path
attribute carried in the BGP UPDATE message and that carried inside the MP_REACH_NLRI to
that of the PEz. 

Is this correct? We find that the outer NEXT_HOP gets converted to that of the RR, but
the internal still points to PEx. Is this vendor behavior incorrect or is there a flaw in
our understanding?

Thanks,
John

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From: Ronald Bonica <[email-masked]>
Date: Wed, 13 Apr 2005 20:36:57 -0400

Hi John,

Normally, route reflectors don't set next-hop-self. If you let PEz relay 
the UPDATE without modifying it at all, things will work fine.

Maybe I am misunderstanding point of your question?

                                         Ron

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From: Pedro Roque Marques <[email-masked]>
Date: Wed, 13 Apr 2005 18:08:33 -0700

John Smith writes:

> So, we configured next-hop-self on the RR thinking that it will
> change the NEXT_HOP path attribute carried in the BGP UPDATE message
> and that carried inside the MP_REACH_NLRI to that of the PEz.

> Is this correct?

Depends on your equipement. It will work as you described on a JunOS
box. You should see PEx use a label assigned by the RR and mpls swap
state for that label installed in the RR.

> We find that the outer NEXT_HOP gets converted to
> that of the RR, but the internal still points to PEx. Is this vendor
> behavior incorrect or is there a flaw in our understanding?

This is vendor defined behaviour, afaik, not standards defined
behaviour. The ieft, imho, should get involved in defining "next-hop
self" behaviour.

  Pedro.

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From: Pedro Roque Marques <[email-masked]>
Date: Wed, 13 Apr 2005 18:12:01 -0700

sorry... mistyped.

> behaviour. The ieft, imho, should get involved in defining "next-hop
			     ^^^^^^
			should NOT