Hallo forum, Any help would be appreciated here as I have looked, read, reconfigured aaarrrgggg :x . I have my 3cx V10 RC2 currently sitting on a laptop whilst I carry out an evaluation which on the whole, is looking pretty good. My laptop is connected to a FritzBox 7270 and I have successfully created two VoIP routes, one to the Fritzbox the other is 'through' the Fritzbox to my ISP but this is where the problem occurs. I currently do not have a static IP with my ISP so in the 'Advanced' tab and 'Registration Settings' of my VoIP provider, I selected 'Specified IP' and entered the IP address for that moment in time, perfect with immediate registration. Now, as we know, IP addresses change over a period of time so, if I understand the use of 'STUN' correctly, I decided to select 'External (STUN resolved) but here is the problem, my 10000 trunk never registers. Something to note here is that with the FritzBox, one MUST change the default SIP/UDP port from 5060 to 'an-other' and I have used the suggestion I found in the forum of 5062. With this change on the 3cx and 'port forwarding' on the FritzBox, I can successfully communicate with all of my internal extensions some of which are connected to another port on the FritzBox. So, back to the trunk route which will not register. Further testing using the softphone sitting on my laptop with the 3cx software, I created a direct account to my ISP, it has to be as an 'I am out of the office - external IP' and here I have placed 'sip.1und1.de', this works 100%. I have also configured accounts on my hardphone extensions, which are connected to other ports on the FritzBox, and these also register 100%. But my 3cx simply will not. Now what I can provide is the following: 12:55:32.171 Currently active calls [none] 12:55:30.515 [CM504007]: Next attempt to register 10000@1und1 is scheduled in 5 minute 12:55:30.515 [CM504005]: Registration failed for: 10000@1und1; Cause: 403 Keine RFC1918-IPs erlaubt; from IP:18.104.22.168:5060 12:55:30.421 [CM504003]: Sent registration request for 10000@1und1 12:55:00.171 Currently active calls [none] 12:54:32.937 [CM506001]: STUN request to resolve SIP external IPort mapping is sent to STUN server 22.214.171.124:3478 over Transport 192.168.178.28:5062 12:54:28.171 Currently active calls [none] According to the 'General Configuration Information when using VoIP Providers', after the [CM506001}, I should also see a [CM506002] but as can be seen, or not as the case is, I do not 'see' the [CM506002]: Resolved SIP external IP..... Could this be the reason as to why my registration attempts are sending out the private IP address and hence failing 403 RFC1918. I think that sums it up for the mo, as I say, I have been looking at this for @2 weeks now and getting absolutely nowhere so any help would be appreciated. Antler.