The Protocol Filter is an application layer packet classifier. The service attempts to identify an application as data packets pass through the gateway and classify them according to known protocols. If successfully identified, user sessions can be blocked based on an administrator's preference and/or policy.
With more and more applications like file-sharing and Internet Messaging abusing standard ports designated for legitimate services, the protocol filter app can be a valuable tool in an administrator's desire to control what types of traffic are allowed on the network.
To learn more about this app, click here
Documentation for ClearOS 6 can be found here.
Documentation for ClearOS 7 can be found here.