IGPs in use

Alex Bligh amb at gxn.net
Tue Oct 13 19:09:47 UTC 1998


Jared,
> 
> 	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)

No argument with the principles here but why do you need to redistribute
connected interfaces into your IGP *and* into iBGP? Overkill, surely?
IMHO all you need do is put appropriate connected interfaces and statics
pointing out of your core into either the IGP *or* iBGP. Whether you
do this via redistribution or not is probably network dependent.

In case anyone hadn't realized (I'm sure Jared did), (2) ensures you
carry round the iBGP next hop of the loopback addres of the exit router
rather than (say) the next hop over the NAP concerned, which some
idiot is bound to leak a more specific of just when you've forgotten
to filter it. This also removes the nead for carrying the DMZ in your
IGP (or, I suppose iBGP).

Are there really networks out there that chose to run iBGP not only
as an IGP (we do this in one AS), but also don't run something to hold
up the loopback interface mesh too? (i.e. use Chris' auto-discovery method).
Presumably they peer between interface addresses or it's not going to
work as nothing will ever discover an arbitrary /32 loopback. Euch!

-- 
Alex Bligh
GX Networks (formerly Xara Networks)





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