OSPF -vs- ISIS

Tue Jun 21 17:35:01 UTC 2005

On Tue, Jun 21, 2005 at 11:50:59AM -0500, Stephen Sprunk wrote:
> 
> Thus spake "Mike Bernico" <mbernico at illinois.net>
> > The State of Illinois converted to ISIS in 2002 from EIGRP and it
> > has definitely been a good thing for us.  It's been operationally
> > bullet proof, and simple to maintain.
> >
> > We typically get features faster than we would if we ran OSPF.
> > For example, we have a desire in the future to use IPFRR.  Every
> > indication from the vendor is that this feature will be available to
> > ISIS first, most likely because of either the extensibility of ISIS
> > or more likely because ISIS is in so many larger providers.
> 
> This points to something that's really unrelated to the minor technical
> differences between the two protocols: how they're viewed by your vendor.
> 
> One vendor in particular sees ISIS as "an ISP protocol" and OSPF as "an
> enterprise protocol".  Their implementation of the latter has often gotten
> many enterprise-oriented features (e.g. dial-on-demand link support) that
> the other didn't, whereas the former was known for reliability because the
> coders were admonished to touch it rarely and test the heck out of every
> change because screwing up might break the Internet.

To that end, you also need to be aware that outside of the "major"
vendors, most don't even know what ISIS is. So if you're trying to
integrate other vendors' equipment into your network, you may have no
choice but OSPF.

> The difference in stability is less apparent today, but the mindset is still
> quite alive.  That means ISIS gets "ISP" features faster, and the code still
> tends to be more solid than OSPF even though ISIS might now be getting
> changes more frequently than it did in the past.

Personally, I still favor ISIS in provider style networks, especially
as they grow larger but with the passage of time, there really isn't a
great deal of difference between ISIS level 2 only and one great big
area 0 these days. (Personal experience has suggested to me that ISIS
tends to handle that somewhat better but that doesn't say you won't be
just as happy with OSPF.)

So the long and short of it really boils down to your personal
preference.

---
Wayne Bouchard
web at typo.org
Network Dude
http://www.typo.org/~web/