Firewalls: Understanding Your Network's Front Line Defense

The word "firewall" is commonly heard in almost any conversation about network security. They are hailed as being protective and necessary, but the question is: what exactly is a firewall, and what does it do? A firewall can be either a piece of hardware that sits on the network, or it can be a software utility used on a server. Once implemented, a firewall acts as the first line of defense for your network, used to protect your information from outside threats.

There are two types of firewalls; standard firewalls, and application layer firewalls. Standard firewalls, also known as stateful packet inspection firewalls, provide two distinct services – the first being Network Address Translation (NAT), which allows multiple computers on the same Local Area Network to use an internal IP addressing scheme in order to share an IP address on the Internet. Using NAT, the internal IP address is "translated" at the firewall so that only a single IP address is needed for multiple computers to access the Internet. The other function of standard firewalls is basic port protection, which prevents data transmission through certain ports both entering and leaving the network. In this regard, standard firewalls are limited in customizability; however, they are inexpensive, easy to set up, and perfect for networks that may not need complex access controls.

Application layer firewalls provide all the same functionality as standard firewalls, with some added features and flexibility. Rule sets can be defined using an Access Control List (ACL), which allow certain users to access specific servers or to the Internet, while denying that same access to other users or computers. This greatly increases the level of internal security on your network. Along those same lines, application layer firewalls also allow port forwarding, which enables only specified applications to send and receive data through specific ports on the network, while disabling the same port for all other applications.

In addition to fully customizable access control, application layer firewalls are equipped with intrusion detection and event logging. If a possible breach has been committed, the system will notify the administrator and store information about the occurrence in the system event logs.

Both types of firewalls can be installed and managed locally, or administrated remotely by a third party organization, using off-site equipment. The latter is known as managed firewall service.

Standard Firewalls

Network Address Translation (NAT)
Single Internet IP address
Basic port protection
Enable or disable port ranges
Inexpensive and easy to set up
Manage locally or remotely

Application Layer Firewalls

Added features and flexibility
Rule sets via Access Control List (ACL)
Control server access
Port forwarding
Intrusion detection
Event logging
Manage locally or remotely

Managed firewalls are maintained by a company separate from the business using the network. With a managed firewall, you have access to skilled technicians who specialize in firewall management, so human error is reduced. Research time is lowered because the people in charge of the network already know how to operate it, as opposed to local IT staff having to spend time researching how to set up and secure firewalls. Event logs are also reviewed by people who fully understand the nature of the messages, and how to react and respond to them. Cisco equipment is often used, which is standard in the industry. A managed firewall can also provide Virtual Private Network (VPN) service to allow users to log into the company network remotely for the purposes of sending/receiving company e-mail, transferring files, and viewing intranet pages. Managed firewalls also allow easy customization of access control methods, with skilled technicians handling the actual configuration. Network access does not have to be limited to employees; clients may have services available to them that require access to the company network, and these services can be made available through a managed firewall with VPN setup. In some cases, partnered companies may have shared use of a single network. Managed firewalls make setup of all these things quick and easy.