The VpnAddress property returns the IP address assigned to
the active VPN connection. This property uses heuristics to
detect if the system is currently using a Virtual Private Network
(VPN) connection. Because there is no industry standard for how VPN
adapters are identified, it is possible a VPN may not be detected and
the property will return an empty string. If the property does return
an IP address, the VpnAdapter property will return the name of
the VPN adapter.
If this property returns an IP address, it will be the local address
bound to the VPN adapter, not the external IP address. You can check
the value of the ExternalAddress property to determine what
external IP address has been assigned to the VPN adapter. By default,
this property will prefer IPv4 addresses and will only return an IPv6
address if the VPN adapter has not been assigned an IPv4 address.