Hi @Max_Mackenzie,
OMG! it worked!!! I am beyond happy 
The setup was pretty straight forward.
I didn’t have to forward any of the ports you mentioned to get it to work… Is that becuase the VPN server is on the same subnet as the Core server?
I’ve tested it over 4G and it worked perfectly.
One odd thing, I have to disable WIFI for roon to see the iPhone as an audio device. If I don’t it just get stuck trying to enable the audio device. Can you imagine why?
Thanks again for the tips. much appreciated.
For anyone else who wants to give it a go. I did the following:
- Create an SD card image (standard Raspian) with this app: https://www.raspberrypi.org/downloads/
- Booted the Pi with the sd card with a montior, keyboard and mouse.
- Assigned the Pi a fixed ip (DHCP allocated)
- Updated all the software to the latest and enabled SSH and VNC from the menu
- Followed this video pretty much to the letter to setup SoftEther: https://www.youtube.com/watch?v=uOP7XyRweRw
- Port forwarded ports UDP 500 and 4500 to the VPN server.
- Setup an L2TP vpn on my iphone. notes on the fields:
Server: You will need to have a Static public IP or use a DNS service to map to your dynamic
Account: will be the you login name @ Virtual hub name. So if you user is ‘fred’ and your virtual hub was ‘remote’, your login should be ‘fred@remote’
Secret: is the IP pre-shared key from the IPSec/L2TP/EtherIP/L2TPv3 Sever setting page on softether server
Enjoy