Understanding Linux Network Internals

Part V. Internet Protocol Version 4 (IPv4)

The Linux kernel supports many Layer three (L3) protocols, such as AppleTalk, DECnet, and IPX, but this book talks just about the one that dominates modern networking: IP. While IPv4 will be described in detail, IPv6 will be only briefly mentioned as needed. I will not spend much time on the theory behind these protocols, with which you should be somewhat familiar, but I will describe the implementation in Linux. I will focus on aspects of the design that are not obvious or that differ substantially from other operating systems. I will also explain the main drawbacks of version 4 of the IP protocol and show how IPv6 tries to address them. Therefore, while there is both some background theory and some code, I expect the reader to be familiar with the basic IP protocol behavior. Here is what is covered in each chapter:

Chapter 18, Internet Protocol Version 4 (IPv4): Concepts

Introduces the major tasks of the IP layer, and the strategies used.

Chapter 19 Internet Protocol Version 4 (IPv4): Linux Foundations and Features

Shows how the IP-layer reception routine processes ingress packets, and how IP options are taken care of.

Chapter 20 Internet Protocol Version 4 (IPv4): Forwarding and Local Delivery

Shows how ingress IP packets are delivered locally to the L4 protocol handler, or are forwarded when the destination IP address does not belong to the local host but the host has enabled forwarding.

Chapter 21 Internet Protocol Version 4 (IPv4): ...