by Michael Rash: Linux Firewalls discusses the technical details of the iptables firewall and the Netfilter framework that are built into the Linux kernel, and it explains how they provide strong filtering, Network Address Translation (NAT), state tracking, and application layer inspection capabilities that rival many commercial tools. UK, Germany
Linux Networking Clearly Explained
by Bryan Pfaffenberger: Topics covered: The practicalities of building LANs under Linux and doing useful work with them, Internet connections via KPPP, TCP/IP configuration, Network File System (NFS), Samba for interaction with Windows, AppleTalk for talking to Mac OS machines, and backups with tar and cron. UK, Germany
Linux Networking Cookbook
by Carla Schroder: This soup-to-nuts collection of recipes covers everything you need to know to perform your job as a Linux network administrator, whether you're new to the job or have years of experience.
TCP/IP Architecture, Design and Implementation in Linux
by Sameer Seth, M. Ajaykumar Venkatesulu: This book provides thorough knowledge of Linux TCP/IP stack and kernel framework for its network stack, including complete knowledge of design and implementation. UK, Germany
Understanding Linux Network Internals
by Christian Benvenuti: this book clearly explains the underlying concepts and teaches you how to follow the actual C code that implements it.