These threats lead to the creation of the firewall technology in order to protect a computer or network of computer which is connecting to the internet.
A firewall is defined as a "computer, router, or other communication device that filters access to the protected network" (Abie 2000). Thus, it gives the implication about the main tasks of a firewall. Accordingly, a firewall inspects traffic network passing through it and is responsible for permitting or denying access. In addition, Cheswick and Bellovin specifies certain processes which characterizes a firewall which include: "all traffic from inside to outside, and vice-versa, must past through it; only authorized traffic, as defined by the local security policy, is allowed to pass through it; and the firewall itself is immune to penetration" (Abie 2000). In summary, a firewall serves as a filter allowing the access of a trusted network and rejecting "untrusted" ones.
The emergence of firewall technology occurs during 1980s far before the internet has gained popularity in global users. Traditionally, a firewall is a term used to denote a "wall to confine a fire or potential fire within a building (Firewall 2008)." The use of firewall in internet has been triggered by the attack of Morris Worm making internet connection vulnerable to its adverse effects. Because of what happened, the whole community becomes aware of the realities of such attack which can threaten the computers accessing the internet (Firewall 2008). Thus, the online community sought for a protection in order to ward off the threat of viruses, worms, and other which can be very harmful and disruptive to the internet users. This is when firewall technology came into being (Firewall 2008).
The beginnings of first generation firewall technology can be traced to the paper released by engineers of Digital Equipment Corporation in 1988 (Firewall 2008). This is referred to as packet filter firewalls which lays down the foundation of a technology that will further be improved and developed. Thus, after the work of these engineers, companies like AT&T Bell Labs and scientists Bill Cheswick and Steve Bellovin continued the long process of research and released a more efficient and complicated versions (Firewall 2008).
Packet filtering is a firewall technology which acts by "inspecting the packets which represent the basic unit of data transfers between computers on the internet" (Firewall 2008). A packet filtering router typically filter packets based on four fields namely, source IP address, destination IP address, TCP/UDP source port, and TCP/UDO destination port (Chadwick 2004). These functions of packet filter are used to block connection from specific hosts or networks, to specific hosts or networks, from specific ports, and to specific ports. Because of their relative simplicity, this type of firewall perform only basic operations including "examining the packet header, verifying the IP address, the port or both, and granting and denying access without any changes" (Abie 2000). Packet filters are regarded for their speed and