This manual, which is part of the Linux Documentation Project, contains a introduction to the TCP/IP protocols and covers various topics related to configuring networking services. http://www.tldp.org/LDP/nag/
This free electronic book in html format covers not only the TCP/IP protocols but also the configuration of most of the applications a network administrator must maintain http://www.dmsa.unipd.it/andreap/nag/nag.html