IP Encapsulation Support

OSPF is a TCP/IP-based protocol and fully supports IP. On the other hand, IS-IS is a native OSI protocol and must still be implemented using ISO addressing for the IS-IS aspects of its operation. IS-IS allows the forwarding of IP packets although not specifically designed to do so.

Available Resources

You must be pragmatic when selecting a routing protocol. Resources should be available to assist network engineers at all levels of competence to help them understand the idiosyncrasies of the protocol that you want to implement.

The standards surrounding OSPF are extremely well written thanks to the OSPF Working Group in the Internet Engineering Task Force (IETF); however, the specification does not include a lot of explanation on the "how" and "why."

IS-IS is deployed in some places, but compared to OSPF, it is still considered a niche protocol. Some ISPs are running it, but almost no enterprise networks are using it as of this writing. The IS-IS specification uses ISO language and terms and not IP.

If formal classroom instruction is of interest to you, several dedicated OSPF courses are available; however, few are available on IS-IS.