A great book. Highly recommended.

http://www.amazon.com/Computer-Networks-Third-Approach-Netwo...

Of course, one of the classics is this one:

Internetworking with TCP/IP vol. 1.

http://www.amazon.com/Internetworking-TCP-Vol-1-Principles-A...

Edit: If you are considering Linux, then the implementation is discussed here. I would not suggest this, unless you are actually hacking. In that case, this is okay:

http://www.amazon.com/Understanding-Network-Internals-Christ...