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TCP/IP Networking 
TCP/IP Illustrated, Volume 1 (W. Richard Stevens) [Mirror] [Mirror] [Mirror] [PDF]
The TCP/IP Guide (C.M. Kozierok) DNS for Rocket Scientists
Teach Yourself TCP/IP in 14 Days, 2nd Edition (Tim Parker) [Mirror] [Mirror] [PDF] [PDF]
Daryl's TCP/IP Primer Guide to Domain Name Service (DNS)
TCP/IP and IPX Routing Tutorial IP Addressing and Subnetting
Understanding IP Addressing (by Chuck Semeria) [Mirror] [Mirror] [Another]
A TCP/IP Tutorial (T. Socolofsky, C. Kale)