well, i wanted play with my friends via lan so i started a listen server. i was behind an adsl router and ns was setup to my internal ip which was 192.168.1.3 but i was shocked when ppl joined my server from the internet. i didnt forward any port or so by then.
then i started a dedicated server for internet play and forwarded ports etc. if i dont use the command +ip it works fine (with the ip 192.168.1.3) but when i add +ip xxx.xxx.xxx.xxx it says couldn't allocate dedicated server ip port. i know that the port is not used by any other program and i tested if port is open and it is. how can i report my real ip to the steam servers and make the dedicated server work?

You can't set the IP for HLDS to your remote IP because your computer is not bound to your remote IP, it is only bound to your local IP. Only your router knows about your remote IP, not your computer.

As far as reporting your remote IP to steam servers, that I don't know, but it may just be automagic. Steam may take the source IP of the server data being sent to the steam servers, in which case you wouldn't have to do anything, and apparently you don't if people from the internet were joining your game before.