I just installed IPC 7.0.3 on a system with a non-supported VPN. The VPN does create a virtual NIC and is assigned an IP address from the LAN subnet so it does work (for the most part).
My situation is a little different than other posters I've seen. Here are my scenarios:
1. IPC on the LAN = all works fine.
2. Outside calls over VPN (PSTN to IPC or IPC to PSTN) = all works fine.
3. Inside calls over VPN (IPC to Cisco handset) = one way audio. Handset user doesn't hear IPC user but IPC user hears handset user.
The interesting thing is the IPC caller can leave a voicemail message if the handset user doesn't pick up.
I've installed the IPC Administration Tool and enabled HTTP access. The getIP.asp file is accessible. I also put the URL in the IP Address Auto Detection URL field.
Because the audio from the IPC (via VPN) can get to the Unity server but not to the handset user, I'm not sure I understand how this could be a firewall issue.
Thanks in advance.