Linux Networking Cookbook

1. Introduction to Linux Networking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.0 Introduction 1
2. Building a Linux Gateway on a Single-Board Computer . . . . . . . . . . . . . . . . . 12
2.0 Introduction 12
2.1 Getting Acquainted with the Soekris 4521 14
2.2 Configuring Multiple Minicom Profiles 17
2.3 Installing Pyramid Linux on a Compact Flash Card 17
2.4 Network Installation of Pyramid on Debian 19
2.5 Network Installation of Pyramid on Fedora 21
2.6 Booting Pyramid Linux 24
2.7 Finding and Editing Pyramid Files 26
2.8 Hardening Pyramid 27
2.9 Getting and Installing the Latest Pyramid Build 28
2.10 Adding Additional Software to Pyramid Linux 28
2.11 Adding New Hardware Drivers 32
2.12 Customizing the Pyramid Kernel 33
2.13 Updating the Soekris comBIOS 34
3. Building a Linux Firewall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.0 Introduction 36
3.1 Assembling a Linux Firewall Box 44
3.2 Configuring Network Interface Cards on Debian 45
3.3 Configuring Network Interface Cards on Fedora 48
3.4 Identifying Which NIC Is Which 50

3.5 Building an Internet-Connection Sharing Firewall on a Dynamic
WAN IP Address 51
3.6 Building an Internet-Connection Sharing Firewall on a Static
WAN IP Address 56
3.7 Displaying the Status of Your Firewall 57
3.8 Turning an iptables Firewall Off 58
3.9 Starting iptables at Boot, and Manually Bringing Your Firewall
Up and Down 59
3.10 Testing Your Firewall 62
3.11 Configuring the Firewall for Remote SSH Administration 65
3.12 Allowing Remote SSH Through a NAT Firewall 66
3.13 Getting Multiple SSH Host Keys Past NAT 68
3.14 Running Public Services on Private IP Addresses 69
3.15 Setting Up a Single-Host Firewall 71
3.16 Setting Up a Server Firewall 76
3.17 Configuring iptables Logging 79
3.18 Writing Egress Rules 80
4. Building a Linux Wireless Access Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
4.0 Introduction 82
4.1 Building a Linux Wireless Access Point 86
4.2 Bridging Wireless to Wired 87
4.3 Setting Up Name Services 90
4.4 Setting Static IP Addresses from the DHCP Server 93
4.5 Configuring Linux and Windows Static DHCP Clients 94
4.6 Adding Mail Servers to dnsmasq 96
4.7 Making WPA2-Personal Almost As Good As WPA-Enterprise 97
4.8 Enterprise Authentication with a RADIUS Server 100
4.9 Configuring Your Wireless Access Point to Use FreeRADIUS 104
4.10 Authenticating Clients to FreeRADIUS 106
4.11 Connecting to the Internet and Firewalling 107
4.12 Using Routing Instead of Bridging 108
4.13 Probing Your Wireless Interface Card 113
4.14 Changing the Pyramid Router’s Hostname 114
4.15 Turning Off Antenna Diversity 115
4.16 Managing dnsmasq’s DNS Cache 117
4.17 Managing Windows’ DNS Caches 120
4.18 Updating the Time at Boot 121