All traffic between the internal and external network must go through the firewall.
Only authorized traffic is allowed to pass through.
The firewall itself is immune to penetration.
Small and simple enough for rigorous analysis
Service Control – determines the types of services allowed.
Direction Control – determines the direction in which services may be initiated.
User Control – determines which activities are allowed based on the user.
Behavior Control – determines how services are used.
Types of Firewalls
Filtering Firewall – performs access control based packet header attributes, such as destination and source addresses, ports, and other various options. (Routers)
Protects against IP address spoofing, source routing attacks, and tiny fragment attacks.
Stateful Inspection Firewall – tightens security by keeping track of outbound connections. Only allows incoming traffic to high-numbered ports for packets that conform to the entries in the directory.
Types of Firewalls Continued
Proxy Firewall – uses proxies to perform access control. This type of firewall can base control on the contents of packets and messages, as well as on attributes of the packet headers. (Application Proxy, Application-Level Gateway, Guard)
Circuit-Level Gateway – Like a proxy firewall, but once connections are established it does not examine contents. Just determines what connections are allowed.
Personal Firewall – application that runs on workstations to block unwanted traffic.
A firewall can not protect against attacks that bypass the firewall.
A firewall does not protect against internal threats.
The firewall does not protect against virus-infected files.
How a Firewall Can Protect Against a SYN Flood
The SYN Flood is handled before it reaches the firewall.
Examples - Cisco Routers and Synkill
TCP State and Memory Allocations
Make availability of space more likely.
Examples – SYN Cookies and adaptive time-out
Bishop, M. (2003). Computer Security, Art and Science. Boston: Addison Wesley.
Campus Firewall, Frequently Asked Questions . Retrieved March 30 th , 2003, from http://netman.cis.mcmaster.ca/firewallfaq.htm
Pfleeger, C., & Pfleeger, S. (2003). Security in Computing. New Jersey: Prentice Hall.
Stallings, W. (2003). Network Security Essentials, Applications and Standards. New Jersey: Prentice Hall.