Opening ports for remote access on ZyXEL DSL modem

I have to do this once in a while, then completely forget how it's done, and one year later, I spend 1 hour trying to figure it out again. Well, at least on the Prestige 660RU-T1 it's fairly easy from the web interface: NAT -> SUA Only and add something like:

Start Port No. End Port No. IP Address
1All ports All ports

Oh and just in case you wonder, the only mode of authentication allowed from the outside is private key, so good luck trying to break in!