I'm tasked with implementing VPN access on a gateway. The LAN DHCP server is configured to assign the same IP address to a given MAC address. I would like to have this functionality for clients who connect over the VPN. I know I can configure openVPN and strongSwan to use a 3rd party DHCP server, but do daemons use the client MAC address for the DHCP request? Everything I've read doesn't go into this detail, but I imagine it would use the TAP interface MAC address. Am I wrong about this? How much work would it be to configure/patch the VPN server software to achieve this functionality?
with openVPN, any traffic from clients in ethernet bridged mode using 3rd party DHCP is passed with the client's tap0 mac address intact. So if the client has a consistent mac address for their tap0 adapter, you can then allocate them the same IP everytime. I'm not sure if the same behaviour occurs using openVPN's built in DHCP.