Linux LAN & Internet Firewall Security FAQ

Robert L. Ziegler, rlz@world.std.com

1. Purpose of this FAQ

2. Thanks

3. Installation Notes

• 3.1 Hardware Needed for a Home LAN
• 3.2 Before You Begin
• 3.3 Keeping a Windows Partition
• 3.4 Swap Space
• 3.5 Choosing Packages to Install
• 3.6 Configuring TCP/IP Networking
• 3.7 Accessing Memory Above 64MB
• 3.8 Selecting Services to Start Automatically on Reboot

4. Identifying Multiple Ethernet Cards

5. Changing the Network Card's MAC Address

6. Enabling the DHCP Client for Dynamic IP Addresses

7. Network Security Strategies

• 7.1 Packet-Level Filtering
• 7.2 Port-Level Filtering
• 7.3 Firewalling & IP Masquerading Example
• 7.4 Service-Level Filtering

8. What Did I Miss?

• 8.1 Debugging Your Filtering Rules
• 8.2 Checking Port Usage with netstat -a
• 8.3 Checking Processes with ps aux
• 8.4 Setuid and Setgid Programs

9. Vigilance & Error Logs

10. Keeping Up to Date

11. Avoiding Paranoia

12. Re-compiling the Kernel

13. Running lilo

14. Configuring Your LAN

• 14.1 Windows Setup
• 14.2 Macintosh Setup

15. Finishing Up

16. Appendix 1: Configuring SSH

• 16.1 What is SSH?
• 16.2 Features
• 16.3 Quick Configuration
• 16.4 Starting sshd

17. Appendix 2: Configuring NTP

• 17.1 Quick Configuration
• 17.2 Adding the Servers to /etc/hosts/
• 17.3 Initializing the Clock at Boot Time
• 17.4 Updating the Clock on a Daily Basis

18. Appendix 3: Configuring a DNS Caching & Forwarding Nameserver

• 18.1 Configuring DNS Caching in RedHat 5.1 and earlier
• 18.2 Configuring DNS Caching in RedHat 5.2 and later
• 18.3 Configuring DNS Caching in All Versions
• 18.4 Configuring an Internal DHCP Server for the LAN