Blocked ports

Ports are like doors for a special service to a server or PC. They rank from 0 to 65535. The standard ports are from 0 to 1024, these are the well known ports. The official list you can get under http://www.iana.org/assignments/port-numbers and a description on http://www.encyclopedia-online.info/Port_(computing). If a censor blocks a port, every traffic on this port is dropped, so its useless for you. Most censors blocks the ports 80, 1080, 3128 and 8080, because these are the common proxy ports. Because all of the proxies on common ports are useless for you, you have to find proxies that are listening on an uncommon port. These are very difficult to find.

You can easily test which ports are blocked on your connection. Just open the DOS-prompt, type "telnet login.icq.com 80" and hit enter. The number is the port you want to test. If you get some wired symbols in return everything is ok, if it says "timeout" or something similar, that port is blocked by your ISP.

Here are the most important ports for us:

20+21 - FTP (file transfer)
22 - SSH (secure remote access)
23 - telnet (unsecure remote access) and also Wingates (special kind of proxies)
25 - SMTP (send email)
53 - DNS (resolves an URL to an IP)
80 - HTTP (normal web browsing) and also a proxy
110 - POP3 (receive email)
443 - SSL (secure HTTPS connections)
1080 - Socks proxy
3128 - (Squid) proxy
8000 - (Junkbuster) proxy
8080 - Proxy