Changes

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== Configuring Firewall Port Settings ==

The main area of the Security Level Configuration tool consists of a list of TCP/IP based services. Next to each entry is a check box that controls whether the service is trusted, and as such whether or not the corresponding TCP/IP port is open to traffic on the firewall or not (such as port 80 for a web server).

Masquerading is better known in networking circles as Network Address Translation (NAT). When using a CentOS system as a gateway to the internet for a network of computers, masquerading allows all of the internal systems to use the IP address of the CentOS system when communicating over the internet. This has the advantage of hiding the internal IP addresses of any systems from malicious external entities and also avoids the necessity to allocate a public IP address to every computer on the network.

This service is also provided by most routers and gateways so this feature of the CentOS Firewall is rarely used.