http://www.pcvr.nl/tcpip/ -- "TCP/IP Illustrated vol. 1" by W. Richard Stevens, 1st edition
This edition is quite old. Examples of commands may need to be modified to work on your
system (as they come from the Solaris branch of Unix). Still, fundamentals of protocols
have not changed since then, and the book's text is more concise than 2nd edition.

http://www.kohala.com/start/tcpipiv1.html -- source code for TCP/IP Illustrated vol.1
(You may explore the site http://www.kohala.com/start/ for information about Richard Stevens.
 I highly recommend his books if you want to be a master systems or networks programmer.)

https://github.com/sergev/Unix-Network-Programming-1st-Edition -- code from R. Stevens' 
"Unix Network Programming" 1st edition (obtained from http://www.kohala.com/start/unp.tar.Z) 
I find this code simpler, cleaner, and easier to read than that of subsequent editions.
Examples of TCP and UDP clients and servers are in net/ .

http://advancedlinuxprogramming.com/alp-folder/ - free book "Advanced Linux 
Programming". Look in Section 5.5.6 for sample code using Internet sockets for
an HTTP connection.