Firewall Security Tasks

A firewall that does packet filtering addresses the tendency of hackers to open an attack by scanning for network addresses and open ports. (A port is a virtual gateway on a computer through which a particular type of data is allowed to pass. Each port is assigned a number between 0 and 65,535). Initially, a hacker uses special software to scan a series of addresses, attempting to connect to a computer on each one. If any computer answers, it gives the hacker a target. Any gateway or router acting as a packet filter on your network or in your firewall should be configured to reject connection requests from computers that are not on your network.

Note that a port number combined with a computer’s IP address constitutes a network connection called a socket. Software that is commonly used by hackers attempts to identify sockets that respond to connection requests. The sockets that respond can be targeted to see if they have been left open or if they have security vulnerabilities that can be exploited. Some protocol examples include:

  • Simple Mail Transport Protocol (SMTP) listens on port 25
  • Post Office Protocol, version 3 (POP3) listens for incoming mail on port 110
  • Hypertext Transport Protocol (HTTP) Web services use port 80

Restricting Access from Outside the Network

The most obvious goal of a firewall is to regulate which packets of information can enter the network. To do so, a firewall examines each packet to determine whether it meets the necessary “authorized” criteria. The criteria might be protocols or IP addresses on an “approved” list. Anything not on the list is excluded.

Restricting Unauthorized Access from Inside the Network

In some ways, it is relatively easy to protect a network from the Internet but more difficult to protect it from an inside attack. You should be aware of the following possibilities:

  • Virus-infected thumb drive
  • People using direct access to office computers from home using remote access software that bypasses the perimeter firewall
  • Social engineering
  • Poorly trained firewall administrators
  • Employees who receive e-mail messages with executable attachments
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