Understanding Linux Network Internals (Paperback)

Description

If you've ever wondered how Linux carries out the complicated tasks assigned to it by the IP protocols -- or if you just want to learn about modern networking through real-life examples -- Understanding Linux Network Internals is for you.

Like the popular O'Reilly book, Understanding the Linux Kernel, this book clearly explains the underlying concepts and teaches you how to follow the actual C code that implements it. Although some background in the TCP/IP protocols is helpful, you can learn a great deal from this text about the protocols themselves and their uses. And if you already have a base knowledge of C, you can use the book's code walkthroughs to figure out exactly what this sophisticated part of the Linux kernel is doing.

Part of the difficulty in understanding networks -- and implementing them -- is that the tasks are broken up and performed at many different times by different pieces of code. One of the strengths of this book is to integrate the pieces and reveal the relationships between far-flung functions and data structures. Understanding Linux Network Internals is both a big-picture discussion and a no-nonsense guide to the details of Linux networking. Topics include:

• Key problems with networking
• Network interface card (NIC) device drivers
• System initialization
• Layer 2 (link-layer) tasks and implementation
• Layer 3 (IPv4) tasks and implementation
• Neighbor infrastructure and protocols (ARP)
• Bridging
• Routing
• ICMP

Table of Contents

Preface

Part I. General Background

1. Introduction

     Basic Terminology

     Common Coding Patterns

     User-Space Tools

     Browsing the Source Code

     When a Feature Is Offered as a Patch

2. Critical Data Structures

     The Socket Buffer: sk_buff Structure

     net_device Structure

     Files Mentioned in This Chapter

3. User-Space-to-Kernel Interface

     Overview

     procfs Versus sysctl

     ioctl

     Netlink

     Serializing Configuration Changes

Part II. System Initialization

4. Notification Chains

     Reasons for Notification Chains

     Overview

     Defining a Chain

     Registering with a Chain

     Notifying Events on a Chain

     Notification Chains for the Networking Subsystems

     Tuning via /proc Filesystem

     Functions and Variables Featured in This Chapter

     Files and Directories Featured in This Chapter

5. Network Device Initialization

     System Initialization Overview

     Device Registration and Initialization

     Basic Goals of NIC Initialization

     Interaction Between Devices and Kernel

     Initialization Options

     Module Options

     Initializing the Device Handling Layer: net_dev_init

     User-Space Helpers

     Virtual Devices

     Tuning via /proc Filesystem

     Functions and Variables Featured in This Chapter

     Files and Directories Featured in This Chapter

6. The PCI Layer and Network Interface Cards

     Data Structures Featured in This Chapter

     Registering a PCI NIC Device Driver

     Power Management and Wake-on-LAN

     Example of PCI NIC Driver Registration

     The Big Picture

     Tuning via /proc Filesystem

     Functions and Variables Featured in This Chapter

     Files and Directories Featured in This Chapter

7. Kernel Infrastructure for Component Initialization

     Boot-Time Kernel Options

     Module Initialization Code

     Optimized Macro-Based Tagging

     Boot-Time Initialization Routines

     Memory Optimizations

     Tuning via /proc Filesystem

     Functions and Variables Featured in This Chapter

     Files and Directories Featured in This Chapter

8. Device Registration and Initialization

     When a Device Is Registered

     When a Device Is Unregistered

     Allocating net_device Structures

     Skeleton of NIC Registration and Unregistration

     Device Initialization

     Organization of net_device Structures

     Device State

     Registering and Unregistering Devices

     Device Registration

     Device Unregistration

     Enabling and Disabling a Network Device

     Updating the Device Queuing Discipline State

     Configuring Device-Related Information from User Space

     Virtual Devices

     Locking

     Tuning via /proc Filesystem

     Functions and Variables Featured in This Chapter

     Files and Directories Featured in This Chapter

Part III. Transmission and Reception

9. Interrupts and Network Drivers

     Decisions and Traffic Direction

     Notifying Drivers When Frames Are Received

     Interrupt Handlers

     softnet_data Structure

10. Frame Reception

     Interactions with Other Features

     Enabling and Disabling a Device

     Queues

     Notifying the Kernel of Frame Reception: NAPI and netif_rx

     Old Interface Between Device Drivers and Kernel: First Part of netif_rx

     Congestion Management

     Processing the NET_RX_SOFTIRQ: net_rx_action

11. Frame Transmission

     Enabling and Disabling Transmissions

12. General and Reference Material About Interrupts

     Statistics

     Tuning via /proc and sysfs Filesystems

     Functions and Variables Featured in This Part of the Book

     Files and Directories Featured in This Part of the Book

13. Protocol Handlers

     Overview of Network Stack

     Executing the Right Protocol Handler

     Protocol Handler Organization

     Protocol Handler Registration

     Ethernet Versus IEEE 802.3 Frames

     Tuning via /proc Filesystem

     Functions and Variables Featured in This Chapter

     Files and Directories Featured in This Chapter

Part IV. Bridging

14. Bridging: Concepts

     Repeaters, Bridges, and Routers

     Bridges Versus Switches

     Hosts

     Merging LANs with Bridges

     Bridging Different LAN Technologies

     Address Learning

     Multiple Bridges

15. Bridging: The Spanning Tree Protocol

     Basic Terminology

     Example of Hierarchical Switched L2 Topology

     Basic Elements of the Spanning Tree Protocol

     Bridge and Port IDs

     Bridge Protocol Data Units (BPDUs)

     Defining the Active Topology

     Timers

     Topology Changes

     BPDU Encapsulation

     Transmitting Configuration BPDUs

     Processing Ingress Frames

     Convergence Time

     Overview of Newer Spanning Tree Protocols

16. Bridging: Linux Implementation

     Bridge Device Abstraction

     Important Data Structures

     Initialization of Bridging Code

     Creating Bridge Devices and Bridge Ports

     Creating a New Bridge Device

     Bridge Device Setup Routine

     Deleting a Bridge

     Adding Ports to a Bridge

     Enabling and Disabling a Bridge Device

     Enabling and Disabling a Bridge Port

     Changing State on a Bridge Port

     The Big Picture

     Forwarding Database

     Handling Ingress Traffic

     Transmitting on a Bridge Device

     Spanning Tree Protocol (STP)

     netdevice Notification Chain

17. Bridging: Miscellaneous Topics

     User-Space Configuration Tools

     Tuning via /proc Filesystem

     Tuning via /sys Filesystem

     Statistics

     Data Structures Featured in This Part of the Book

     Functions and Variables Featured in This Part of the Book

     Files and Directories Featured in This Part of the Book

Part V. Internet Protocol Version 4 (IPv4)

18. Internet Protocol Version 4 (IPv4): Concepts

     IP Protocol: The Big Picture

     IP Header

     IP Options

     Packet Fragmentation/Defragmentation

     Checksums

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

     Main IPv4 Data Structures

     General Packet Handling

     IP Options

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

     Forwarding

     Local Delivery

21. Internet Protocol Version 4 (IPv4): Transmission

     Key Functions That Perform Transmission

     Interface to the Neighboring Subsystem

22. Internet Protocol Version 4 (IPv4): Handling Fragmentation

     IP Fragmentation

     IP Defragmentation

23. Internet Protocol Version 4 (IPv4): Miscellaneous Topics

     Long-Living IP Peer Information

     Selecting the IP Header's ID Field

     IP Statistics

     IP Configuration

     IP-over-IP

     IPv4: What's Wrong with It?

     Tuning via /proc Filesystem

     Data Structures Featured in This Part of the Book

     Functions and Variables Featured in This Part of the Book

     Files and Directories Featured in This Part of the Book

24. Layer Four Protocol and Raw IP Handling

     Available L4 Protocols

     L4 Protocol Registration

     L3 to L4 Delivery: ip_local_deliver_finish

     IPv4 Versus IPv6

     Tuning via /proc Filesystem

     Functions and Variables Featured in This Chapter

     Files and Directories Featured in This Chapter

25. Internet Control Message Protocol (ICMPv4)

     ICMP Header

     ICMP Payload

     ICMP Types

     Applications of the ICMP Protocol

     The Big Picture

     Protocol Initialization

     Data Structures Featured in This Chapter

     Transmitting ICMP Messages

     Receiving ICMP Messages

     ICMP Statistics

     Passing Error Notifications to the Transport Layer

     Tuning via /proc Filesystem

     Functions and Variables Featured in This Chapter

     Files and Directories Featured in This Chapter

Part VI. Neighboring Subsystem

26. Neighboring Subsystem: Concepts

     What Is a Neighbor?

     Reasons That Neighboring Protocols Are Needed

     Linux Implementation

     Proxying the Neighboring Protocol

     When Solicitation Requests Are Transmitted and Processed

     Neighbor States and Network Unreachability Detection (NUD)

27. Neighboring Subsystem: Infrastructure

     Main Data Structures

     Common Interface Between L3 Protocols and Neighboring Protocols

     General Tasks of the Neighboring Infrastructure

     Reference Counts on neighbour Structures

     Creating a neighbour Entry

     Neighbor Deletion

     Acting As a Proxy

     L2 Header Caching

     Protocol Initialization and Cleanup

     Interaction with Other Subsystems

     Interaction Between Neighboring Protocols and L3 Transmission Functions

     Queuing

28. Neighboring Subsystem: Address Resolution Protocol (ARP)

     ARP Packet Format

     Example of an ARP Transaction

     Gratuitous ARP

     Responding from Multiple Interfaces

     Tunable ARP Options

     ARP Protocol Initialization

     Initialization of a neighbour Structure

     Transmitting and Receiving ARP Packets

     Processing Ingress ARP Packets

     Proxy ARP

     Examples

     External Events

     ARPD

     Reverse Address Resolution Protocol (RARP)

     Improvements in ND (IPv6) over ARP (IPv4)

29. Neighboring Subsystem: Miscellaneous Topics

     System Administration of Neighbors

     Tuning via /proc Filesystem

     Data Structures Featured in This Part of the Book

     Files and Directories Featured in This Part of the Book

Part VII. Routing

30. Routing: Concepts

     Routers, Routes, and Routing Tables

     Essential Elements of Routing

     Routing Table

     Lookups

     Packet Reception Versus Packet Transmission

31. Routing: Advanced

     Concepts Behind Policy Routing

     Concepts Behind Multipath Routing

     Interactions with Other Kernel Subsystems

     Routing Protocol Daemons

     Verbose Monitoring

     ICMP_REDIRECT Messages

     Reverse Path Filtering

32. Routing: Linux Implementation

     Kernel Options

     Main Data Structures

     Route and Address Scopes

     Primary and Secondary IP Addresses

     Generic Helper Routines and Macros

     Global Locks

     Routing Subsystem Initialization

     External Events

     Interactions with Other Subsystems

33. Routing: The Routing Cache

     Routing Cache Initialization

     Hash Table Organization

     Major Cache Operations

     Multipath Caching

     Interface Between the DST and Calling Protocols

     Flushing the Routing Cache

     Garbage Collection

     Egress ICMP REDIRECT Rate Limiting

34. Routing: Routing Tables

     Organization of Routing Hash Tables

     Routing Table Initialization

     Adding and Removing Routes

     Policy Routing and Its Effects on Routing Table Definitions

35. Routing: Lookups

     High-Level View of Lookup Functions

     Helper Routines

     The Table Lookup: fn_hash_lookup

     fib_lookup Function

     Setting Functions for Reception and Transmission

     General Structure of the Input and Output Routing Routines

     Input Routing

     Output Routing

     Effects of Multipath on Next Hop Selection

     Policy Routing

     Source Routing

     Policy Routing and Routing Table Based Classifier

36. Routing: Miscellaneous Topics

     User-Space Configuration Tools

     Statistics

     Tuning via /proc Filesystem

     Enabling and Disabling Forwarding

     Data Structures Featured in This Part of the Book

     Functions and Variables Featured in This Part of the Book

     Files and Directories Featured in This Part of the Book

Index