[c-nsp] RE: [cisco-bba] L2TP tunnel persistence and routing

Mark Tohill Mark at u.tv
Fri Feb 24 04:50:41 EST 2006

Thanks Oliver.

This is exactly what we done and its working well.

I did however manage to bring down the router by putting a debug
condition on internal interface and a debug vpdn l2x-packets to try and
prove l2tp traffic no longer traveling over that link.

I'll learn....

Thanks again,

-----Original Message-----
From: Oliver Boehmer (oboehmer) [mailto:oboehmer at cisco.com] 
Sent: 10 February 2006 11:51
To: Mark Tohill; cisco-bba at puck.nether.net
Cc: cisco-nsp at puck.nether.net
Subject: RE: [cisco-bba] L2TP tunnel persistence and routing

Mark Tohill <> wrote on Friday, February 10, 2006 12:34 PM:

> We have 2 x 7200's terminating VPDN DSL traffic.
> Each router has a Gig fibre link to providers switching
> infrastructure and have an eBGP peering, both announcing PoP space. 
> In order to create tunnels, providers net depends on BGP to reach our
> tunnel endpoints, one on each box. Due to current BGP announcements,
> this means tunnels for both boxes arrive on the first box. L2TP
> traffic destined to be terminated on second box travels over internal
> gig link.    
> We want to change this either via statics being implemented by
> Provider or using BGP /32 announcements for our Loopback. 
> Would such diversion of L2TP traffic bound for second box bring down
> the tunnels i.e users ? 

No, it should not affect the established tunnels, the packets will just
re-route along the more-specific route. 
If the provider agrees, I would do this dynamically by announcing /32,
they will then likely tag them with no-export so the announcements stay
local to their AS.


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