In the past, many ISPs (Internet Service Providers) began blocking or throttling peoples Usenet connections to outside Newsgroup Servers.  This was done because most ISPs provided Usenet and they wanted to discourage people from reading Newsgroups from other providers which could use a lot of the ISPs Internet bandwidth.  Although most ISPs no longer provide Usenet on their own networks, it is still common for many ISPs to block or throttle Usenet for the same reason, bandwidth.In order to be able to provide better service to more people, most NNTP server providers allow alternate ports that a subscriber can use to connect to their Newsgroup servers.  By using alternate ports it is more difficult for an ISP to use technologies, such as traffic-shaping to place caps on only Usenet users.  If you have noticed that your Usenet downloads seem significantly slower than downloading in your web browser, your ISP might be throttling your connection, and using an alternate port could help you to get around it.

Some ISPs have used software in the past which is able to recognize the protocol that is being used on a port, and based on the type of traffic they can throttle or block your Usenet.  Although NNTP and HTTP use plain-text messages to transfer data back and forth, the commands and responses (although using similar result codes) are different enough to be easily differentiated. Because of this, and privacy concerns, Usenet providers also allow users to connect to their NNTP servers securely, using 256-Bit SSL connections, which render the content of dialog between a Usenet client and the Usenet server, unreadable or recognizable.

Below is a table with various commercial Usenet providers and the optional ports you can use to connect to them.

Ports Used

Almost all of the ports used by Newsgroup servers as alternates are actually defined for a specific purpose. This is done so that ISPs will be more reluctant to simply block the port and thus interfere with other users ability to use those services. Below is a table which tells what service typically is run on each port.