Which of these four books is recommended for gaining a deeper insight into the TCP/IP suite?

I would like to gain a deeper insight into the TCP/IP suite.

I've seen four books recommended. I don't wish to read them all, as they will most likely have overlapping knowledge.

The books are:

1. Routing TCP/IP, Volume 1
2. TCP/IP Illustrated, Volume 1: The Protocols
3. Internetworking with TCP/IP, Volume 1
4. The TCP/IP Guide (Licensed PDF Version)

Which of these four should I get?

Thank you.