How do countries, like China, block web sites that they feel are not appropriate?

I’m not quite sure, but it seems to me that the IP addresses are specific to people in certain countries. The Governmnet regulates the internet in the certain country, and if an IP that is in that country tries to access a blocked site, they are denied access.

Then again, I don’t know, so don’t take my words for granted.

to the best of my knowledge its like a giant proxy. Like at school where they can determine which sites are accessible and which are not.

Uberbatman is probably right… Why don’t you jsut google it? Unless you already have.

Internet Service Providers in mainland China are required by law to participate in the Chinese government’s filtration scheme. This includes a number of technical methods, which I will outline below. All of these methods are through the use of a nationwide firewall (http://en.wikipedia.org/wiki/Firewall) system, all of which use the same censorship schema. This system has been dubbed by many as the “Great Firewall of China”.

IP blocking. Access to a certain IP address is denied. If the target website is hosted in a shared hosting server, all websites on the same server will be blocked. This affects all IP-based protocols such as HTTP, FTP and POP. A typical circumvention method is to find proxies that have access to the target websites, but proxies may be jammed or blocked, and some websites, such as Wikipedia (when editing), also block proxies. Some large websites like Google have allocated additional IP addresses to circumvent the block, but later the block was extended to cover the new IPs.

DNS filtering and redirection. Don’t resolve domain names, or return incorrect IP addresses. This affects all IP-based protocols such as HTTP, FTP and POP. A typical circumvention method is to find a domain name server that resolves domain names correctly, but domain name servers are subject to blockage as well, especially IP blocking. Another workaround is to bypass DNS if the IP address is obtainable from other sources and is not blocked. Examples are modifying the Hosts file or typing the IP address instead of the domain name in a Web browser.

URL filtering. Scan the requested Uniform Resource Locator (URL) string for target keywords regardless of the domain name specified in the URL. This affects the HTTP protocol. Typical circumvention methods are to use escaped characters in the URL, or to use encrypted protocols such as VPN and TLS/SSL.

Packet filtering. Terminate TCP packet transmissions when a certain number of controversial keywords are detected. This affects all TCP-based protocols such as HTTP, FTP and POP, but Search engine results pages are more likely to be censored. Typical circumvention methods are to use encrypted connections – such as VPN and TLS/SSL – to escape the HTML content, or by reducing the TCP/IP stack’s MTU/MSS to reduce the amount of text contained in a given packet.

Connection reset. If a previous TCP connection is blocked by the filter, future connection attempts from both sides will also be blocked for up to 30 minutes. Depending on the location of the block, other users or websites may also be blocked if the communication is routed to the location of the block. A circumvention method is to ignore the reset packet sent by the firewall.

Web feed blocking. Increasingly, incoming URLs starting with the words “rss”, “feed”, or “blog” are blocked.

Reverse surveillance. Computers accessing certain websites including Google are automatically exposed to reverse scanning from the ISP in an apparent attempt to extract further information from the “offending” system.

You can find out more at Wikipedia’s article on Internet Censorship (http://en.wikipedia.org/wiki/Internet_censorship).

Guess I wasn’t too far off with the IP Address Issue. I was still kinda off though.