Blocking content coming into and going out to the Internet. Accomplished by firewall software residing in a stand-alone device, router or user's machine or in a filtering program in each user's machine, content can be blocked based on website address or Internet service. For example, users might be allowed access to the Web but not to file transfers (FTP).
Websites and Internet Services
Incoming content can be blocked for specific users or for all users. Blocked websites can be recognized by their Web address (URL) or by elements within the URL. All traffic is identified by port number, and an entire service can be blocked by this number. For example, websites use port 80 and file transfers are 20, 21 and 22 (see well-known port
In the home, parents can restrict their children's access with special browsers and filtering programs (see parental control software