Baker, F., ed. “Requirements for IP Version 4 Routers,” RFC 1812, June 1995. This paper documents both requirements and recommendations for routers that will run IP.
Braden, R., ed. “Requirements for Internet Hosts—Communication Layers,” RFC 1122, October 1989. The host-centric companion paper to RFC 1812.
Comer, D. E. Internetworking with TCP/IP, Vol. 1. Englewood Cliffs, New Jersey: Prentice-Hall; 1991. This book, like Perlman's, is a classic. Although you don't need to read both Comer and Stevens, doing so certainly couldn't hurt.
Stevens, W. R. TCP/IP Illustrated, Vol. 1. Reading, Massachusetts: Addison-Wesley; 1994. An excellent book on TCP/IP. Along with an in-depth introduction to the protocols, Stevens offers a wealth ...