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

Oliver Boehmer (oboehmer) oboehmer at cisco.com
Fri Feb 10 06:50:44 EST 2006

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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