Local DHCP doesnt work when OpenVPN is enabled

[davids@btni.co.uk]

Hi,
I have managed to get the OpenVPN connection working from my Yealink T28 to FreePBX OpenVPN, however this was using a static IP address on the phone. As soon as I turn it to DHCP the phone just sits on obtaining IP address.

We need them to be configured to use DHCP so that normal users can take the phones home and plug into the home networks, no matter what way their home networks are configured.

Ideally it should get a local IP address first, and then dial the VPN and get its tunnel address and finally find the PBX.

As soon as I give the phone a static IP address it connects to the VPN and registers against FreePBX.

If I turn off VPN it will pick up a dhcp address straight away (after it reboots) so I know my dhcp server is ok.

Some specs
T28P
Firmware 2.73.0.50
Windows 2012R2 DHCP - no VLAN - 192.168.xx.xx network
OpenVPN network - 10.0.8.xx
I have tried the phone through two different PoE switches, cisco and netgear.

I will gather up some logs and post then here shortly, but thought I would put the question out in case someone has came across this issue before.
Thanks
David

Update - No logs are recorded on the windows server, and as the phone gets rebooted before I can connect to it, its logs don't show anything before the reboot. Correct me if i'm wrong or if you know how I can see the logs of it failing to get a dhcp address?
Thanks