Feuerfest

When I setup my Termix instance I used port 6666/tcp. However on my first visit I wasn't greeted with a Termix login page, rather a Firefox message appeared. One I had never encountered before.

Huh? What? I use all kinds of strange ports in my home network and never got that error message.

I was kind of annoyed that there was no button labeled "I know the risk, take me there anyway".

However a quick search showed the solution.

1. Open about:config
2. Enter: network.security.ports.banned.override
   • The key doesn't exist per-default
3. Create it as type "String"
4. Add the port number
   • If multiple ports are needed specify them as a comma separated list: 6666,7777

This is how it looks in my case:

What ports are blocked? And why?

If we look at the source code, we see the list of ports that is blocked: https://searchfox.org/firefox-main/source/netwerk/base/nsIOService.cpp#122

In total just shy over 80 ports are blocked. And there seems to be no separation between UDP or TCP ports.

A bit more Firefox context is in their Knowledge Base: https://kb.mozillazine.org/Network.security.ports.banned

They get this port list from the "The Web Hypertext Application Technology Working Group (WHATWG)" who define a list of "bad ports" in this document: https://fetch.spec.whatwg.org/#port-blocking

Apparently "A port is a bad port if it is listed in the first column of the following table.", well you never stop learning. 😉