How to get network adapter index?

Question

From code I want to force a Windows machine to use a specific network adapter for all connections to a specific IP address.

I plan to do so by using the ROUTE ADD command line tool, but this requires that I know in advance the network adapters' index number (as it must be given to the ROUTE ADD command).

QUESTION: How can I programmatically retrieve a network adapter's index, given I know its name?

I'm aware that ROUTE PRINT shows me the information I need (the index numbers of all network adapters present), but there must be a way to get that information programmatically too (C#)?

Note, that I don't like parsing the text output from ROUTE PRINT, as the text format may change with different Windows versions.

Solution

You can obtain the interface index of your network adapter by using the .Net NetworkInterface (and related) classes.

Here is a code example:

static void PrintInterfaceIndex(string adapterName)
{
  NetworkInterface[] nics = NetworkInterface.GetAllNetworkInterfaces();
  IPGlobalProperties properties = IPGlobalProperties.GetIPGlobalProperties();

  Console.WriteLine("IPv4 interface information for {0}.{1}",
                properties.HostName, properties.DomainName);


  foreach (NetworkInterface adapter in nics)
  {               
    if (adapter.Supports(NetworkInterfaceComponent.IPv4) == false)
    {
      continue;
    }

    if (!adapter.Description.Equals(adapterName, StringComparison.OrdinalIgnoreCase))
    {
      continue;
    }
    Console.WriteLine(adapter.Description);                                
    IPInterfaceProperties adapterProperties = adapter.GetIPProperties();                
    IPv4InterfaceProperties p = adapterProperties.GetIPv4Properties();
    if (p == null)
    {
      Console.WriteLine("No information is available for this interface.");                    
      continue;
    }                
    Console.WriteLine("  Index : {0}", p.Index);              
  }
}

Then just call this function with the name of your network adapter:

PrintInterfaceIndex("your network adapter name");

You can also obtain the InterfaceIndex of your network adapter by using the Win32_NetworkAdapter WMI class. The Win32_NetworkAdapter class contains a property called InterfaceIndex.

So, to retrieve the InterfaceIndex for a network adapter with a given name, use the following code:

ManagementScope scope = new ManagementScope("\\\\.\\ROOT\\cimv2");

ObjectQuery query = new ObjectQuery("SELECT * FROM Win32_NetworkAdapter WHERE Description='<Your Network Adapter name goes here>'");           
using (ManagementObjectSearcher searcher = new ManagementObjectSearcher(scope, query))
{
  using (ManagementObjectCollection queryCollection = searcher.Get())
  {             
    foreach (ManagementObject mo in queryCollection)
    {                 
      Console.WriteLine("InterfaceIndex : {0}, name {1}", mo["InterfaceIndex"], mo["Description"]);
    }
  }
}

If you do not want to use WMI you could also use the Win32 API function GetAdaptersInfo in combination with the IP_ADAPTER_INFO struct. You will find an example here pinvoke.net.

Comments

[Martin Christiansen]

Yes I have, but it doesn't seem to give me the information I need. Try for yourself to enter ROUTE PRINT from a command line and look at the first table displayed. The index numbers I need are in the leftmost column (each line lists <index number>...<MAC address>...<Adapter Name>).

[Martin Christiansen]

Hi Hans - your code looks very promising - I will try it out tomorrow as first thing in the morning, when I get back on work.

[Martin Christiansen]

Hi Hans - your code looks very promising, I will try it out tomorrow as first thing when I get back on work. However, earlier today I tried using the WMI approach, and I listed all properties available for each network adapter, but I did not see any propterty named "InterfaceIndex" - maybe I just overlooked it? I'm using Windows XP Professional SP3. I'll let you know what I find out tomorrow. Thank you very much for your involvement, it's fantastic to have people like you around!

[Hans]

@MartinChristiansen: This WMI property is not available under Windows XP.

[Martin Christiansen]

That explains why I did not see it. However, I have now tried your first code example, and it works like a charm - even with XP. You certainly saved my day - thanks al lot!