Firewalls What Are They, What Do They Do, and What Do They Protect Against?
What Are Security Policies For?
What Does a Packet-Filtering Firewall Do?
Services Provided by or in Conjunction with a Firewall
Tri-Homed Bastion with DMZ and LAN
Section 2 TCP/IP Concepts Underlying a Packet-Filtering Firewall
IP Information Available to a Stateless Firewall
ICMP Packet Header Internet Control Message Protocol
UDP Packet Header User Datagram Protocol
TCP Packet Header Transmission Control Protocol
TCP Connection Establishment 3-Way Handshake
Section 3 Packet-Filtering Concepts
Rejecting Versus Denying a Packet
Allowing Incoming Packets from only Specific Remote Source Addresses
Local Destination Port Filtering
TCP Connection State Filtering
Section 4 What Do Static Firewalls Protect Against?
What Can a Stateless Firewall Protect Against?
Importance of Blocking Outgoing Spoofed Source Addresses
Revealing Useful Information in Response to Port Scans
Block Connections to Insecure Services Running on Unprivileged Ports
Limit Access to Sensitive or Easily Exploitable Services
Packet Fragmentation - Teardrop
Section Four What a Stateless ipchains Firewall Cannot Protect Against