Is my ISP filtering my outgoing network ports?

Some Internet Service Providers (ISPs) intentionally block their customers from being able to connect to various servers on various ports. For example, they might allow you to connect to servers on ports 80 and 443 (for normal web traffic), but they may block you from connecting to servers on port 5900 (for Remote Desktop) or ports 6881-6889 (for BitTorrent). Often they won't tell you that they're doing this; we've also heard that some ISPs only filter certain ports at various times of day.

We've built a tool which will check whether devices on your internet connection can connect to certain ports on remote servers or whether they've been filtered. This tool will attempt to connect to one of our special testing servers on lots of different ports and then show you which ports worked which ones didn't.

Experimental tool

This tool is most definitely an experimental/beta test. Currently it only supports Chrome and Firefox. (They also don't seem to work on iOS yet either - just desktop). We hope to expand support later. If there are other ports we don't scan for that you would like to see included in the list, just let us know.

We are gauging interest in this tool, so if it helped you then tell us and we'll know to spend more time on it!

Unsupported browser

Sorry, but right now this tool only supports Firefox and Chrome. We'll make it work with other browsers soon!


Web browsers can't check every port

Please note; as a security measure, there are a number of ports which web browsers won't ever allow you to connect to. This prevents website visitors being unwitting accomplices in hacking or denial of service attempts were they to ever visit a dangerous website. As such, there are some ports (such as port 21 (FTP), port 22 (SSH), port 25 (SMTP), port 143 (IMAP) etc) which we are unable to test for filtering. You can see that we've greyed those ports out in the listing above - we'll never test them.

Unfortunately this means that this tool can't confirm that connections to your Mail server, FTP server, SSH server etc are or are not being blocked/filtered. Note that the lists of ports which are blocked by the browser are a bit different between browsers - The Chrome and Firefox port-block lists are slightly different.

You always could use a tool like NetCat, nmap or even plain old Telnet to see if you can connect.

We can only check for TCP connections

Unfortunately* we can only check if your ISP is filtering or allowing TCP traffic. Web browsers can't make UDP requests so there's no way to check for that protocol using your web browser. Hopefully checking TCP still gives you enough of an idea of your filtering situation. We think that it's likely that if an ISP is filtering UDP traffic on a particular port, they're also probably filtering TCP traffic as well, so this tool may still give you accurate enough results.

*Please note, it's not really unfortunate... measures like this actually prevent serious security attacks!