User guide

User Guide 7
Introduction to Network Security
About Firewalls
A firewall separates your trusted computers on the internal network from the external network, or the
Internet, to decrease risk of an external attack. The figure below shows how a firewall divides the trusted
computers from the Internet.
Firewalls use access policies to identify and filter different types of information. They can also control which
policies or ports the protected computers can use on the Internet (outbound access). Many firewalls have
sample security policies, and users can select the policy that is best for them. With others, including the
Firebox, the user can customize these policies.
Firewalls can be in the form of hardware or software. A firewall protects private networks from unauthorized
users on the Internet. All traffic that enters the trusted or protected networks must go through the firewall.
The firewall examines each message and denies those that do not match the security criteria or policies.
In some closed, or default-deny firewalls, all network connections are denied unless there is a specific rule to
allow the connection. To deploy this type of firewall, you must have detailed information about the network
applications required to meet your organization’s needs. Other firewalls allow all network connections that
have not been explicitly denied. This type of open firewall is easier to deploy, but it is not as secure.