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  • What is a firewall
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      Firewalls
    What is a Firewall:
    A Firewall is a method for implementing security policies designed to keep a network secure from intruders. Firewalls installed to protect entire networks are typically implemented in hardware; however, software firewalls are also available to protect individual work stations from attack.
    This illustration shows the physical relationship between a network and the Internet using a Hardware firewall.
    Firewalls use one or more of three methods to control traffic flowing in and out of the network:
    • Packet filtering - Packets (small chunks of data) are analyzed against a set of filters. Some methods of filtering are listed below.

    • Proxy service - Information from the Internet is retrieved by the firewall and then sent to the requesting system and vice versa. This method is used with websites, so there is no direct access to the server.

    • Stateful inspection - A newer method that doesn't examine the contents of each packet but instead compares certain key parts of the packet to a database of trusted information.
    software firewalls:
    A software firewall, such as ZoneAlarm, can be installed on the computer in your home that has an Internet connection. This computer is considered a gateway because it provides the only point of access between your home network and the Internet.
    hardware firewalls:
    With a hardware firewall, the firewall unit itself is normally the gateway. Some examples would be a D-Link or Linksys Cable/DSL router. They have a built-in network cards and also operate as a switch. Computers in your home network connect to the router, which in turn is connected to either a cable or DSL modem. You configure the router via a Web-based interface that you bring up through the browser on your computer.
    Depending on the firewall you are using you may be able to customize how it filters.
    • IP addresses - a firewall can identify an ip address and block traffic to or from that IP address
    • Domain names - you are able to block or allow specific domain names
    • Protocols - some of the protocols you may be able to block or allow are:
      IP, TCP, HTTP, FTP UDP, ICMP, SMTP, SNMP, Telnet
    • Ports - a server makes its services available to the Internet using numbered ports, you can allow or disallow use of these ports
    • You may also be able to block specific words or phrases
    When to Use a Firewall:
    Generally, if you have a "dial-up" connection, you will not need a firewall. You are connected for relatively short periods of time, so your computer is not as vulnerable as it would be if connected for long periods of time. Every time you dial in you receive a different ip address, this will also protect your computer.

    If you have high speed "digital subscriber line", dsl, you will want to use a firewall. A hardware firewall, a router, will allow you to have multiple computers connected to the router so they can all access the Internet and each other.

    If you are running a server that is on all the time and accessible from the Internet, you will want to have a firewall.
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