DhcpEnumSubnets

[DllImport("dhcpsapi.dll", SetLastError = true)]
public static extern uint DhcpEnumSubnets(
   IntPtr ServerIpAddress,
   ref uint ResumeHandle,
   uint PreferredMaximum,
   ref IntPtr SubnetInfo,
   ref uint ElementsRead,
   ref uint ElementsTotal
);

Microsoft documentation: Link