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In this article:
- What is a firewall
- History of firewall
- Types of firewall
What is a Firewall
A firewall is a computer program (software) or hardware that performs the important function of stopping unauthorized access to a computer connected to a network. The extent to which a firewall monitors and prevents traffic over a network from reaching a particular computer system is determined by the network security policy defined on the computer system. A firewall may also be called a Border Protection Device (BPD) or packet filters. A firewall determines or marks certain zones, each having a certain (or no) level of trust. A firewall then controls the traffic moving between a zone of complete trust or high trust and a zone of no or very low trust. A typical example would be that of a computer system (the trusted zone) and the Internet (a zone of no trust). This way, any unwanted programs or other types of infection are prevented from entering the trusted zone.
History of Firewalls
Firewalls have existed since Internet was in its nascent stages in the 1980s. The reason for the creation of firewall software was the increase in the increase in the number of internet security violations such as the Morris worm, attributed to be the first widely spread Internet worm.
The technology behind firewalls was first introduced by Jeff Mogul in the form of a paper in 1988. The system that he created was very basic but it laid the foundation for what would grow into very technologically advanced security software. In the 1990s, Dave Presetto and Howard Trickey made the second generation of firewalls called circuit level firewalls. Marcus Ranum then worked upon the technology underlying the development of proxy firewalls. The resultant product was released in the market by Digital Equipment Corporation (DEC) who named it the SEAL.
In 1994, the Israeli company Check Point Software Technologies released the software firewall called FireWall-1. A second generation of proxy firewalls was based on Kernel Proxy technology. Since then, firewall technology has come a long way.
Types of firewalls
Firewalls are distinguished from one another on the basis of the following criteria:
- Scope of communication:
Firewalls may work in situations where there is only a single node or computer system communicating with a network or there maybe two or more networks communicating with each other. On this basis a firewall maybe one of the following:
- Personal Firewall
These are software programs which filter the traffic that enters a single computer system to and fro a network it is connected to
- Network Firewalls
These firewalls are placed between the boundaries of the two or more networks that are communicating with each other. Usually, they are placed on their own dedicated server or other network device
- Interception Layer:
A firewall may either monitor or intercept the traffic at the network layer or at the application layer. On this basis, the following types of firewalls maybe identified –
- Network layer firewalls
Network layer firewalls monitor the traffic at the network level and completely stop the suspicious traffic from entering the network or single node
- Application layer firewalls
These firewalls intercept traffic at the Application Layer of the TCP/IP network protocol. Thus, all traffic such as that of Telnet, FTP etc. are monitored
- Operating System firewalls
These are lower in the hierarchy as compared to application layer firewalls and they only control the operating system or other system software
- State tracking
Some firewalls may or may not track the state of the communication being done over a connection. On this basis, two types of firewalls maybe identified:
- Stateful firewalls
These types of firewalls monitor the traffic and also keep record of the state of the network connections from where the data came
- Stateless firewalls
These types of firewalls inspect each packet in complete isolation of other packets received and does not keep any record of the state of the connection that they came from
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