Naturally, the authorities of any country in the world filter Internet content. Everyone filters the most appropriate things for them. In the USA they block gambling websites, in Europe - the sites containing Nazi symbols, in China and Belorussia they block the websites of political opponents. Recently Iran joined the censoring team and some of their technologies can even beat those of China with their Great China Firewall.

Below is the list of technological means used by the government of different countries for filtering Internet traffic.

1. IP blocking.

A standard means of Internet filtering which is very popular among the authorities of many countries including Russia and Belorussia. It is not effective with P2P communications and proxy servers.

2. Traffic Categorization. (QoS)

A more effective technology functioning on the basis of disabling the traffic directed through certain protocols and ports. It is mainly aimed at decreasing the general flow of traffic in a particular segment of the Web and consequently, the workload for the monitoring system are usually rather resource-intensive, especially when it comes down to deep content filtering.

3. Packet Name Inspection.

In fact, packet name inspection is a way of DPI, or deep packet inspection. Here, only the names of the packets are subjected to inspection. But this technology is far less efficient than DPI, as it is normally used for filtering large amounts of information. For example, using this technology means easier identifying of all SSL packets which are further subjected to other means of more efficient and deeper inspection. The ubiquitous use of DPI enables the civil right activists to mislead the enemy which was successfully carried out in Iran during converting SSL traffic into FTP packets names.

4. Packet Properties Inspection.

It is a more advanced way of content filtering as it deals not only with the names of packets but also their size measured in bits, the frequency of transmission and other characteristics that can identify the type of content. Intelligence services use this technology to block SSH traffic preserving the efficiency of corporate VPN that are transferred through the same protocol.

5. Deep Packet Inspection or Content Filtering.

The most advanced and resource-intensive way of traffic filtering that deals with inspecting the contents of the packets. This security means can only be overcome with traffic crypto.

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