[c-nsp] LAC for PPPoE with multiple links to LNS

[Warwick Duncan]

Hi

We're planning a network of a couple of thousand remote sites connecting
with PPP to a central router (we're thinking a Cisco ASR 1002-X).  For
most sites we can get ethernet to the central router and can use PPPoE
but for several hundred we have to go via a third party's layer 3
network, where the layout could be as follows:

  Site 1 --                         -- layer 3 upstream -\
  Site 2 -- Aggregation point (LAC) -- layer 3 upstream -- ASR (LNS)
  Site 3 --                         -- layer 3 upstream -/

i.e. we connect a handful of sites (between 2 and 20) with ethernet to a
central point at which we buy multiple layer 3 upstream links, all from
the same provider, to give the required bandwidth.  For reasons beyond
our control, a single link can't provide adequate bandwidth for even a
single site.

The obvious starting point, unless we're missing something, is to put an
L2TP LAC at the aggregation point and tunnel the PPP to the central ASR,
which we configure as an LNS.  This achieves our goal of having a PPP
session between the ASR and each site.

How do we elegantly aggregate the multiple layer 3 links between LAC and
LNS into a single logical bundle?  If it can't be elegant, what's the
least ugly way to do it?

I don't think multilink PPP is applicable in this scenario (it would be
between Site N and LAC, had the multiple links been there) but I'd
happily be proved wrong.

It would be nice to guard against equipment failure at the aggregation
point.  Is there a way to put up 2 LAC's with the upstream links split
between them, yet still provide any single site with the full aggregated
bandwidth of all upstream links?

Lastly, would something like a 3640 be an adequate LAC for, say, 12Mbps
upstream (6 x 2Mbps serial links)?  Are there any gotchas with doing
MPLS over PPP on an ASR 1002-X?

Thanks for reading this far...

Regards
Warwick

-- 
Warwick Duncan
Frogfoot Networks ISP
http://www.frogfoot.com/
+27.21.448.7225