So I'm managing a few 3CX installs now, and I regularly move between accounts on my softphone to check for activity on the phone system before sending firmware updates, or other things that might disrupt service. I have one of my clients that I cannot register my softphone to their system. It will just sit and loop on Registering... Register Failed. I have watched the traffic both leaving my network and as it enters in my client's network. I see that on normal registration, there will be a TCP 5090 packet, then UDP 5090, and then TCP 5001. For the one that won't register, there is only TCP 5090 going. The UDP 5090 never even leaves my machine. Why would only this site be failing to register? Every account is installed directly from the config file in the welcome email. Any ideas?