Whether you're a network administrator or just starting out in the IT world, knowledge and understanding of TCP/IP is requirement.  Download this just published, free online book TCP/IP Fundamentals for Microsoft Windows and have that information at your fingertips.  It a soup to nuts guide covering everything from an overview of TCP/IP, IP addressing and subnetting (ah... the fun stuff, bring back the TCP/IP MCP exam!!!), IP Routing, Dynamic Configuration Protocol and much, much more. 

From the download page:

Overview

This online book is a structured, introductory approach to the basic concepts and principles of the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol suite, how the most important protocols function, and their basic configuration in the Microsoft Windows Vista, Windows Server 2008, Windows XP, and Windows Server 2003 families of operating systems. This book is primarily a discussion of concepts and principles to lay a conceptual foundation for the TCP/IP protocol suite and provides an integrated discussion of both Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6).