Finding a VPN Connection's IP Address

I want a script that can tell me the IP address of a VPN connection on a VPN client. Do you have any ideas about how to do this?

Determining the IP address of an established VPN connection can be useful when you want to know whether a particular VPN tunnel is established. For example, if split tunneling is enabled, you might use this IP address to add entries to your routing table. (See http://www.microsoft.com/technet/community/columns/cableguy/cg1003.mspx for more information about split tunneling.)

As you might already know, the Windows Management Instrumentation (WMI) Win32_NetworkAdapter and Win32_NetworkAdapterConfiguration classes provide a host of properties and methods that deal with the system's network adapters and associated configurations. However, neither class has a dedicated WMI property that determines whether an adapter is a VPN adapter.

I've found that connected Microsoft VPN adapters have a description beginning with WAN Miniport in the Win32_NetworkAdapter class. (Other vendors' proprietary VPN clients will likely have a different description.) However, this class doesn't include the IPEnabled or IPAddress properties that we need to narrow our search—those properties are in the Win32_NetworkAdapterConfiguration class. To work around this problem, we can use the Win32_NetworkAdapterSetting associator class (WMI associator classes connect two associated classes) to retrieve the relevant properties.

We need a solution that first uses the Win32_NetworkAdapterConfiguration class to retrieve the collection of IP-enabled network adapters, then, for each instance in this collection, retrieves the associated Win32_NetworkAdapter instance, and finally, returns the first IP address in the Win32_NetworkAdapterConfiguration instance's IPAddress property if the Win32_NetworkAdapter instance's Description property starts with WAN Miniport. GetVPNIP.vbs, which Listing 3 shows, implements these steps in VBScript. GetVPNIP.js, which Listing 4 shows, is the corresponding JScript implementation.

At callout A in Listing 3 and Listing 4, the script executes a WMI query that returns a collection of IP-enabled Win32_NetworkAdapterConfiguration instances. Next, the script iterates each instance in the collection. The code at callout B in Listing 3 and Listing 4 uses WMI's AssociatorsOf() method to retrieve the Win32_NetworkAdapter object that's associated with the Win32_NetworkAdapterConfiguration object via the Win32_NetworkAdapterSetting class. (See http://www.microsoft.com/technet/scriptcenter/topics/networking/02_ atnc_basic.mspx for information about how the two classes are associated.) The AssociatorsOf() method returns a collection of Win32_NetworkAdapterSetting instances, which the script iterates with another For Next loop. If the associated Win32_Adapter object's Description property starts with WAN Miniport, the script echoes the first IP address in the Win32_ NetworkAdapterConfiguration object. (The IPAddress property is an array, and the script echoes only the first item of that array.)

As I said, this information likely applies only to Microsoft VPN adapters; other vendors might approach VPNs differently. For example,-Cisco System's VPN client installs its own adapter, so you would need to modify the scripts in Listing 3 and Listing 4 to match the properties that the Cisco adapter uses.

Bill Stewart (bill.stewart@frenchmortuary .com) is the systems and network administrator for French Mortuary in Albuquerque, New Mexico.