IGPs in use

Tue Oct 13 18:46:02 UTC 1998

On Tue, Oct 13, 1998 at 02:24:23PM -0400, Phillip Vandry wrote:
> > instead of descending into a silly syntax discussion of whether ibgp is an
> > egp or an igp, perhaps the guy would like an answer to his question.
> > 
> > most large nsps use is-is, but usually only to carry the routes of the bgp
> > speaking interfaces.
> 
> Really?? Not that I desire to express any prejudices, but I honestly
> thought nobody used it.
> 
> Does it just work better for very large networks?

	If properly deployed it works in smaller networks well
also.

	I've heard arguments about the amount of cpu time
it takes to do both, but simply put:

	1) If you put your backbone connected interfaces (loopbacks
serials, etc.. in your IGP [isis, ospf, whatever])
	2) Have a full iBGP mesh doing next-hop-self of the loopback
interface
	3) Redistribute statics and connected into your iBGP routing table
(with route-map, or appropriate filters as necessary that vary by vendor)

	Once you've done this, shifting traffic is all about adjusting
your igp metrics, and everything will be advert'ed appropriateley.

	If you are multiply connected to various NSPs, you can send them
the same metrics from your igp in eBGP for the distance away, so they
can make better decisions of where to hand you the traffic (unless
they do hot potato)

	- jared

-- 
Jared Mauch  | pgp key available via finger from jared at puck.nether.net
             | http://puck.nether.net/~jared/