TOPIC:

I'm hosting a tor exit node. What ports must i forbid my node to use in order to avoid being banned automatically?

This means your IP is blacklisted in some services/sites about the matter, like rbl.efnetrbl.org.
Possibly the only solution is stop hosting the TOR node and ask for removal of the black list.
Nothing more we can do.

Note: I'm not expert on the matter so, if anyone has better help, please say

Why won't you ban only the nodes that actually can proxy stuff coming onto your services? Via check.torproject.org/cgi-bin/TorBulkExitList.py for instance, instead of relying on shotgun middleware.

Anyway, looks like providing a free anonymizing service is more important than playing on your servers for me

well, it's your choice!

It's an automated protection software that we use and one of the check sources is rbl.efnetrbl.org.
As I said, you must check there if your IP is blacklisted (for whatever reasons) and ask for removal there, not here ^^

Edit: n-ice servers have the exact same protection because, kindly, n-ice community is letting us use their IRC server to host our channels

Oh, so it actually doesn't care about openttd stuff and checks for irc ports as opposed to banning every exit node regardless of its policy. It's strange that i can't play openttd because of irc :]
Okay, i've banned these and sent them an unban request and they have removed my ip.