BGP Default Route

Jesper Skriver jesper at skriver.dk
Mon Sep 16 07:21:52 UTC 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.



More information about the NANOG mailing list