The .NET Framework SDK provides a helpful utility called mgmtclassgen.exe, which can be used to create .NET-friendly wrappers of the WMI classes. Open up a Visual Studio command prompt and enter the following:

mgmtclassgen Win32_NetworkAdapter -p NetworkAdapter.cs

This will generate a file called NetworkAdapter.cs which will contain a C# representation of the WMI Win32_NetworkAdapter class. You can add this source code file to your C# project and then access all the properties without too much extra effort.

SelectQuery query = new SelectQuery("Win32_NetworkAdapter", "NetConnectionStatus=2");
ManagementObjectSearcher search = new ManagementObjectSearcher(query);
foreach(ManagementObject result in search.Get())
{
NetworkAdapter adapter = new NetworkAdapter(result);

// Identify the adapter you wish to disable here.
// In particular, check the AdapterType and
// Description properties.

// Here, we're selecting the LAN adapters.
if (adapter.AdapterType.Equals("Ethernet 802.3"))
{
adapter.Disable(); // for disable
adapter.Enable(); // for enable
}
}

hope this will help you.

http://www.eggheadcafe.com/community/aspnet/2/10308416/enable-disable-lan-connection-in-cnet.aspx