1. 1 Internet Firewall Security Present by: Ying Fu Department of Computer Science South Eastern University February, 2001

2. 2 Introduction to Internet Firewall Internet is not safe. Internet firewall is a system or group of systems that enforces a security policy between a private network and the Internet. The system is usually a combination of software and hardware. Two Principles: 1. Everything is forbidden except the allowed ones. 2. Everything is allowed except the forbidden ones.

3. 3 Three type of Internet Firewalls 1. Packet-Filtering Firewalls - a permit/deny decision is made based on the packet header information (IP address, Protocol, Port, etc). 2. Application-Level Firewalls - simulates the effect of an application so that the application will receive only requests to act properly. 3. Stateful Inspection Firewalls - pattern matching + state maintenance (remember some state information about current data exchanges).

4. 4 Internet Firewall Examples Figure 1. Packet-filtering firewall

5. 5 Internet Firewall Examples - Cont’d Figure 2. Application-level firewall (Screened Host)

6. 6 Comparison of Types of Firewalls Table 1. Comparison of Types of Firewalls

7. 7 Conclusions  Internet firewall can improve private network security by examining all the packets going through it.  Internet firewall allows the network administrator to define a centralized “check point” where Internet security can be monitored and alarms generated.  Inadequate configuration of firewall can lead to “underground” channel that harm the private network security.  Internet firewall is not a panacea.