It's not an option on the DHCP configuration page - can't have a subnet conflicting with the VPN subnet. Specifying the subnet/mask on the Client VPN configuration page creates the DHCP for IP assignment, but it does not send mask or gateway settings. Which leads to another question - is an MX required at each end of the VPN, remote location and main/headquarters? If so, that would defeat the purpose of remote VPNs in a world of working from home.
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