RDP to bridged VM in DMZ from VPN

[Aloehart]

I'll try and be as descriptive as possible. I'm at the end of my rope sorting this out.

We have a server in a DMZ, Windows server 2012.
We have Virtualbox running 2 VM's on that server, both of which are running Windows Server 2012
The VM's are configured with static IP using a bridged connection.
The VM's are recognized by other systems (including PDQ inventory/deploy) that are in the DMZ.
I can RDP to those VM's from other systems within that DMZ.

While connected to that DMZ via VPN, I cannot RDP from my laptop to the VM directly. It's not able to connect.
I can RDP to a server within the DMZ, then use RDP on that server to connect to the VM's.

I'm not sure where there could be a block preventing the connection.

[BillG]

There are lots of things which could cause it but none that I can think of has anything to do with VirtualBox. Once you set the network mode to bridged, the vm will work exactly like a physical machine as far as networking is concerned. VPN is a much more likely cause.