Thus spake "Mike Bernico" <mbernico@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. 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. S Stephen Sprunk "Those people who think they know everything CCIE #3723 are a great annoyance to those of us who do." K5SSS --Isaac Asimov