Subject: Role of CE routers in BGP MPLS/VPN Switching?

From: "Sugar, Sylvia" <[email-masked]>
Date: Thu, 8 May 2003 11:50:57 +0100 (BST)

Hi,
As per my understanding of 2547bis the BGP CE routers when connect to the BGP PE routers are
unaware of anything and all the work needs to be done by the PE router i.e associating routes
learnt from this CE BGP speaker with some VRF and then attaching some extended community
attributes, etc and announcing to other PE routers (with the label obviously).

Finally, when this PE router recieves routes from other PE BGP speakers then it checks which all
routes need to be announced to this CE router (by examining the Route Target definitions) and does
so. For this CE router this PE router is just another BGP speaking router which is giving it some
BGP routes.

Now when some data traffic comes from this CE router towards the PE router then it puts the BGP
Label associated with the FEC which was advertised to this router by the remote PE router and also
puts another IGP label and pushes the packet out.

This packet gets switched based on the top-most IGP label. Upon reachiong the final router it will
strip off the outermost label (or a router before this will do this), examine the BGP label and
will know what this FEC this corresponds to.

The idea is that the CE routers are unaware of anything happening .. its just the PE routers which
maintain the VRFs, etc. and make the VPN work!

Is my understanding correct?

I would really appreciate if somebody could just confirm that!

Regards,
Sylvia

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