[j-nsp] Re: Conditional advertising of default routes

[Daniel Roesen]

On Thu, Jan 26, 2006 at 10:07:41AM +0200, Pekka Savola wrote:
> On Thu, 26 Jan 2006, Thomas Salmen wrote:
> > You could ask your transit providers to send you a default route as well as
> > full routes?
> 
> If they don't have a default route, they might not want to do so, if 
> that'd mean they'd have to put a default route in their boxes.
> 
> Actually, we have the same issue as Jee Kay.  Using a default route 
> generates all sorts of (difficult-to-notice, and -debug) corner cases, 
> but we really don't want to push full 200K routes on all our routers 
> either..

Jep. Proper default routing is a difficult thing.

The ideal solution would be to have the real tier1s originate default
routes to their BGP downstreams, and those being able to selectively
make those default routes not being used for forwarding, but still
available for re-announcement to their customers who wish to receive
dependable default routes.

One can do this with JunOS by tagging a received BGP default route with
a community, and matching this community on RIB-to-FIB feeding to
discard the route. Still in BGP, but not used for forwarding.

No idea wether this trick can be done with Cisco gear - I cannot
remember them having a way to filter the RIB-to-FIB transfer.


Best regards,
Daniel

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