Pin Me

How Does a Firewall Work

written by: Jayant R Row•edited by: Tricia Goss•updated: 5/8/2010

Many organizations have firewalls that deny access to sites on the internet because they are seen as a security risk or deemed by managements to be completely irrelevant to the business that they are in.

  • slide 1 of 2

    Firewalls Enhance Security


    Administrators on an IT network erect firewalls and control the data to which any computer in the local network can have access based on the requirements of the network users. The main aim of a firewall is to prevent any destructive or obstructive forces that can invade a computer from cyberspace. Its job is similar to a physical firewall that is meant to save property from the effects of fire.

    Firewalls use one of three methods to control the traffic coming in or going out from a network. A set of filters is set up that filter all packets of information. Only data that can go through the filter is accepted. Firewalls can also function by working as proxy servers that take every request for information and send them directly to the system that has requested that information. This limits any damage to the system that has requested the information and helps to trace problems. The latest method for firewalls examines the data in each packet and compares them to the database of information that has been previously vetted and found trustworthy. Packets that do not do not match the information on these databases are rejected.

  • slide 2 of 2

    Configuration of Firewalls

    Firewalls can be customized to fit the security needs of every network as required by the administrator. Filters that govern the data that is allowed into the network can be added or removed. IP addresses are 32-bit numbers that are expressed as four octets in a decimal number that is dotted. A firewall can block all traffic to and from a particular IP address if this is known.

    The most common form of filter is the domain name filter, where an actual domain name is added to the filter. Certain domain names can be completely blocked or granted conditional access. The internet uses certain protocols that define how a particular site or service will correspond with those requesting that service. While IP is the main delivery system, others like FTP are used only to download and upload files. Others in the protocol list are TCP, HTTP, UDP and SMTP, SNMP, Telnet and ICMP. A firewall can be configured to allow only certain protocol to be used by the users on the network it is guarding. This restricts outside sites from gaining easy access to the computers on the network. Normally only certain machines in a network are able to access all types of protocols.

    Firewalls are a must for individual computer users as well. This can save them from hackers and other sites whose main aim is to fish for personal data. Firewalls enable a user to restrict the computer to only those sites that are trusted and known not to have any malicious software or malware on it.