I. Packet-Filtering and Basic Security Measures -- 1. Preliminary Concepts Underlying Packet-Filtering Firewalls -- 2. Packet-Filtering Concepts -- 3. ipatables: The Linux Firewall Administration Program -- 4. Building and Installing a Standalone Firewall -- II. Advanced Issues, Multiple Firewalls, and Perimeter Networks -- 5. Firewall Optimization -- 6. Packet Forwarding -- 7. NAT - Network Address Translation -- 8. Debugging the Firewall Rules -- III. System-Level Security and Monitoring -- 9. Verifying That the System Is Running as You Expect -- 10. Issues at the UNIX System Administration Level -- 11. Secure Shell (SSH) -- 12. Tripwire -- 13. Intrusion Detection and Incident Reporting Software -- IV. Appendixes -- B. Firewall Examples and Support Scripts -- C. VPN