Configuring Security

Understanding Firewalls

A firewall is a method of connecting an internal network to another network while controlling the access in both directions securely. A firewall enables users with the proper privileges to access the internal network. A firewall is not a particular piece of hardware or software, but a combination of software and hardware that protects an internal network from hackers and viruses. A firewall can be one computer with two network cards or several computers working together to provide protection. A proxy server is a type of firewall.

There are three major types of firewalls:

A firewall sits between a client and a server. To the client, a firewall acts like a server, and to the server it acts like a client. Firewalls can be transparent, so that when a client connects to the firewall, it seems like a direct connection.

You can install firewall software to simplify setting up a firewall. Firewall software can provide additional security services, such as screening Domain Name System (DNS) records to prevent disclosure. However, if you use firewall software, you must verify that it supports the applications and protocols you expect to send or receive across the firewall.

For examples of common firewall deployments using Exchange front-end and back-end servers, see the Microsoft Exchange 2000 Server Planning and Installation.

Related Topics

Intranet-to-Internet Communication