All 65k TCP ports, from 1 to 65535, are open on this web server. It is a useful network diagnostic tool to verify if your Internet Service Provider, or company, or home network is blocking outgoing connections to certain port numbers.
To test from a browser, add colon(:) followed by the port number after the hostname. For example, http://open.zorinaq.com:80 tests the default HTTP port. Try other common ports: 8000, 8080, 443. Many ISPs block Windows CIFS/NetBIOS ports 137, 138, 139, 445, or SMTP port 25. Some browsers block ports such as 1, 7, 9, 11, 13, 15, 17, ..., 65535. For ports blocked by Google Chrome, see kRestrictedPorts in net_util.cc. For ports blocked by Mozilla Firefox, see this page.
To test from a Unix shell:
$ telnet open.zorinaq.com 1234
Or GET from libwww-perl:
$ GET http://open.zorinaq.com:1234