SIP registration per IP


I want to recive calls from a single IP, and i need it to do no username/password authentication! how do i do that! it would be nice if i can make this look like as if a certain extension is doing the call, or maybe as an anonymous user, both will be fine … i think … or is there a better way to do it. im still new to asterisk and telephony in general. and btw , i want to allow multiple calls from that ip at the same time too!

in sip.conf
host=dynamic replace dynamic by ip adress and no password.
more info

Thank you reaper, it worked with insecure=port,invite and with host set to the IP . thank you