Stevens, W. Richard; Prentice Hall; 1990; ISBN 0-13-949876-1;
772 pp.; $54 (USA).
Everything you might want to know about the subject, and some things you probably didn't want to know (really, XNS!?). Generally regarded as definitive on the basics, though it's pre-Web.
Kirch, Olaf; O'Reilly; 1995; ISBN 1-56592-087-2; 335pp.
See
http://www.ora.com/catalog/linag/noframes.html.
A practical guide to Linux's TCP/IP and related services. Accessible on the Web at the Linux Documentation Project page, or directly at http://sunsite.unc.edu/LDP/LDP/nag/nag.html.
Hunt, Craig; O'Reilly Associates, ISBN 0-937175-82-X; 1992; 472pp.
See
http://www.ora.com/catalog/tcp2/noframes.html.
Less Linux-specific than the Kirch book. Features deeper coverage of the TCP/IP core, including routing and BGP.
Albitz, Paul, and Liu, Cricket; O'Reilly; 1996; ISBN 1-56592-236-0;
1992; 438pp; $32.95.
See
http://www.ora.com/catalog/dns2/noframes.html.
In-depth coverage of DNS, useful for people running complicated multiple-subnet installations. Covers BIND library programming.
Costales, Bryan & Allman, Eric; O'Reilly;
ISBN 1-56592-222-0; 1997; 1050 pp; $32.95
See
http://www.ora.com/catalog/sendmail2/noframes.html.
An exhaustive (and exhausting) guide to Linux's and Unix's default mail-transfer agent.