What Is Network Filtering Software?
Network filtering software allows a network device to treat different types of traffic with different priorities or security levels. Network traffic is allowed or denied based on a set of rules or conditions that are configured into a network device. Corporate users require complex rules on the firewalls to control Internet access. Personal users rely on commercial software on a PC.
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Packet Structure for Internet Communication
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Networks are built-in layers. Rules for permitting or denying packets use any information within the packet. Packets contain information at several layers. The application puts information inside a TCP Header. The TCP Header is put inside an IP Header. The IP packet is put inside a local area network header, usually Ethernet.
IP Address Filtering
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Packet filters prevent access by unwanted sites. Network filtering software examines each level and, based on preprogrammed rules, allows or denies packets. You can block access to one IP address or a group of IP addresses completely if the computers at that address or addresses are know to attempt software attacks.
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TCP Port Filtering
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Ports are software addresses. Ports are numbers inside the TCP header that identify a process on each computer. When a web browser requests a page from a web server it uses Port 80 as the software address of the web server. An email server usually uses Port 25 and an FTP server uses Port 21. Filtering software can allow packets using Port 25 or Port 80, but deny packets using Port 21. This permits use of the web server or email server, but denies access to the FTP server. Filtering based on the IP address or port number is most common in a corporate IT department.
Application Filtering
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You can filter content on your computer. Filter software restricts access based on the contents of the application data. You need a list of web sites that contain content that you do not to allow on your network. You can restrict website access based on the names or addresses of the server. This is the most common mechanism for home users. The lists of websites that should be restricted must be kept up to date, which is the purpose of the software packages.
Personal Filtering Software
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Filters can be personalized. Application level software is often installed on personal computers and is used to control what websites or FTP sites your computer can access. The personal filtering software often has user names and passwords to allow different users to have different access rights. A university student doing social research might require access to websites that would be unsuitable for younger children. You can configure personal filtering software to control who can access which sites.
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