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Re: BGP Default Route

  • From: Jesper Skriver
  • Date: Mon Sep 16 03:24:14 2002

On Sun, Sep 15, 2002 at 07:32:23PM -0400, Martin, Christian wrote:

> > On Sat, Sep 14, 2002 at 02:18:15PM -0400, Lupi, Guy wrote:
> >
> > > I was wondering how people tend to generate default routes to
> > > customers running bgp.
> >
> > Short answer: don't
> >
> > Longer answer: To solve the exact problems you mention below, only
> > advertise a aggregate block of your own to this customer, say
> > x.x.0.0/16, then the customer will configure his device something
> > like
> >
> > ip route 0.0.0.0 0.0.0.0 x.x.0.0
> > 
> > or
> > 
> > set routing-options static route 0.0.0.0/0 next-hop x.x.0.0 resolve
> > 
> > This will ensure that if the border router get's isolated, it will
> > no longer advertise x.x.0.0/16 to the customer, and the customer
> > router can choose a backup path.
>
> What if the aggregate is local to the border router?  If you want to
> avoid this problem, you will have to use a route that originates from
> somewhere away from the border.

Yes, I guess that is the most normal senario, the aggregate routes are
sourced at a set of routers at different pop's, but not all border
routers.

> This is more work than is necessary, IMO.  If your border router is
> isolated, you have a design problem or a failure state that is just as
> likely to occur(if not moreso) than the border router failing.

That is no argument, there is a probability that a border router get's
isolated, and the above solution will handle that problem too, how
likely or unlikely that failure might be, which highly depends on the
design.

> What I will say is that a "full-table" peer should not get a default
> route at all.

Agree

> Of course, this isn't very enforcable.  In any case, providing a
> default is not something I would say shouldn't be done, IMHO.

/Jesper

-- 
Jesper Skriver, jesper(at)skriver(dot)dk  -  CCIE #5456
Senior network engineer @ AS3292, TDC Tele Danmark

One Unix to rule them all, One Resolver to find them,
One IP to bring them all and in the zone to bind them.




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