"Old" books in some cases, but some protocols never age out! (some of below maybe did...)
Free books on my desk here at work/WPI, if unwanted I'll end up tossing:
(2005) Addison-Wesley "The Design and Implementation of the FreeBSD OS"
I got glassy-eyed diving into most of this kernel,fsys,devices,IPC,etc gore.
(2003) ORA/O'Reilly "DNS & BIND Cookbook" (bind8,9) Cricket Liu 200+ pg paperback
(2003) ORA "LDAP System Administration" Gerald Carter 290pg paperback
(1994) Addison-Wesley "TCP/IP Illustrated, Vol. 1" W. Richard Stevens 550pg hardcover
(1990) Prentice Hall "UNIX Network Programming" W. Richard Stevens 750pg hardcover
( things like fork/exec ; basic I/O ; FIFO,IPC,Sockets,TLI...ending in rlogin :) TOO OLD
(1993) ORA "sendmail" ( v8 ) too old AND too nasty,
though I like the Intro sec1+2 titles "MUA vs MTA" and "Why is sendmail so complex?"