IS-IS questions


I asked on a few days ago about the advantages of
IS-IS over OSPF. Dave Katz replied that IS-IS has proven to be very
extensible while still allowing for backward compatibility. IS-IS was also
overhauled around the same time that a lot of ISPs were building their

My questions are these. When is a good time to use IS-IS? Should an ISP
that wants to build a scalable network go with IS-IS right now? Or is
there a certain point where IS-IS becomes desirable over OSPF? Is there
ever such a point? I would think it is better to pick an IGP and stick
with it.

Thanks for any comments.


Many people seem to use IS-IS for interarea (inter-pop) routing, but use
OSPF intra-pop. It's not that surprising that people use multiple IGPs.
Most people use iBGP to some extent (often without realizing it), even if
their network is statically routed or uses OSPF also.

Of course, there are some Cisco nasties if you use OSPF and have other
equivalent routes laying around...