Beej's guide to network programming
@ https://beej.us/guide/bgnet/
Old but important reference manual for how networks work, however some concepts are dated.
UNIX network programming
@ https://en.wikipedia.org/wiki/UNIX_Network_Programming
Highly rated book for creating networks using UNIX.
TCP/IP illustrated
@ https://en.wikipedia.org/wiki/TCP/IP_Illustrated
First edition is apparently the best. Considered the best explainer for how TCP/IP works.
The Linux Programming Interface
@ https://man7.org/tlpi/
Core concepts for systems programming on Linux, considered one of the best reference books.
Hands on network programming
@ https://handsonnetworkprogramming.com/
A highly rated modern book on networks and creating servers.