IGP choice

Fri Oct 30 13:34:58 UTC 2015

On Thu, Oct 22, 2015 at 12:35 PM, Dave Bell <me at geordish.org> wrote:
> On 22 October 2015 at 19:41, Mark Tinka <mark.tinka at seacom.mu> wrote:
>> The "everything must connect to Area 0" requirement of OSPF was limiting
>> for me back in 2008.
>
> I'm unsure if this is a serious argument, but its such a poor point
> today. Everything has to be connected to a level 2 in IS-IS. If you
> want a flat area 0 network in OSPF, go nuts. As long as you are
> sensible about what you put in your IGP, both IS-IS and OSPF scale
> very well.

It is rather nice that IS-IS does not require level-2 to be
contiguous, unlike area 0 in OSPF.  It is a valid topology
in IS-IS to have different level-2 areas connected by
level-1 areas, though you do have to be somewhat
careful about what routes you propagate into-and-back-out-of
the intervening level-1 area.

But other than that, yeah, the two protocols are
pretty much homologous.

Matt