[c-nsp] MPLS down to the CPE

Mark Tinka mark.tinka at seacom.mu
Wed Jul 10 06:14:36 EDT 2013

On Tuesday, July 09, 2013 07:02:56 PM Phil Bedard wrote:

> In our case we are using separate OSPF areas for the
> access elements, IS-IS wasn't supported when we started
> doing the deployments.  Depending on scale sometimes an
> entire agg location may use the same subtending area,
> sometimes there are more than one, sometimes an area per
> access ring.  The agg/core nodes of each local network
> sits in OSPF Area 0, and the different network islands
> are tied together using CsC over a common MPLS core. 

That sounds hectic, Phil, but I guess it is better than 
virtual links :-).

> I've never liked the
> idea of doing inter-as RSVP-TE except in unique
> situations, I'd rather use areas/levels and hierarchy
> than a stateful session across boundaries.

You're forced to do this when things like p2mp RSVP-TE don't 
support inter-area LSP's.

As always, things will improve to break restrictions, over 

> At the ABR
> all of the L2VPN services are "stitched" since you are
> entering a different RSVP-TE/MPLS domain, the L3VPN
> configuration exists on these nodes with the access
> nodes using L2 pseudowires into virtual L3 interfaces.  
> Cisco talks about a similar architecture in their
> "Unified MPLS for Mobile" presentation from the last
> Cisco Live.  Cisco has always called these ABR/agg nodes
> the "PWHE" or pseudowire headend since they aggregate a
> large number of pseudowires.
> Long-term there are various options to eliminate the
> stitching and associated configuration, although we've
> got it pretty automated at this point.

I will concede that your setup is very, very kinky, but if 
you have it all automated with fluff, then I suppose that is 
okay :-).

> RFC3107 down to
> the access nodes will work but may overwhelm routing
> tables if you have thousands of potential endpoints. 
> You also run into scale issues with terminating BGP
> sessions from access nodes to RRs or ABRs.   Another
> option is have the ABR do RFC3107 to LDP translation
> (supported today) and have the access nodes setup in
> Downstream on Demand mode so they request labels only
> for the destinations they need.  The vendor (A) supports
> longest-prefix match for LDP, including the default
> route, so you don't need to carry /32s in your IGP
> anymore.  Odd Juniper wrote the RFC on that but (A) is
> the only vendor to implement it.

Admittedly, SR (Segment Routing) will simplify things a lot 
(and then you have to worry about scaling the IGP, again).

I'll be honest, your approach is much more complicated for 
me, but I'm glad to hear your story and happy to see how you 
have strung things together. Thanks for that!


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