how to get Client System name On WAN

Question

How can i Get system name using asp.net with vb.net
 
I am using this .
Its working fine on Lan but on WAN it gives me client Ip Instead of Client system Name
 

Kindly Help 
Dim SystemName As String = MachineName(Request.UserHostAddress)


Public Shared Function MachineName(ByVal clientIP As String) As String Try Dim hostEntry = System.Net.Dns.GetHostEntry(clientIP) Return hostEntry.HostName   Catch ex As Exception   End Try