John Moy, “OSPF Version 2,” RFC 2328, April 1998.
John Moy, OSPF: Anatomy of an Internet Routing Protocol. Reading, Massachusetts: Addison-Wesley; 1998.
Written by one of the original designers of OSPF and the author of the RFCs, this book is good reading not only for its excellent coverage of the protocol but also for its historic perspective. Chapter 3 is especially interesting, with its insider's perspective on the design, testing, and standardization of a routing protocol.