To become a CCIE you need detailed knowledge of OSPF. Most candidates will have read the TCP/IP Volumes by Doyle and maybe even the RFC written by J Moy.
This book is also written by J Moy and it is basically the bible on OSPF. The great thing about this book is that is like a less dry version of the RFC and it explains the design decisions in OSPF.
Why did they choose to make it link state instead of distance vector? RIP had issues with large networks and the large updates being sent and your network diameter was limited due to the hop count limit. Why did they choose to run it over IP instead of making it a link layer protocol or run it over UDP or TCP? This is also explained in the book.
Creating a protocol takes a lot of work and making it interoperable is a challenge. Moy describes how they did interoperability tests where the first test was hosted at Proteon. It was a common occurence to see developers from several companies leaning over a competitor’s shoulder, trying to fix a bug!
I’m still reading the book but it has been great so far. I you get a Safari subscription you can read all the books you like. I recently did and I can really recommend it.