How to determine which network adapter is connected to the internet

Question

I'm writing a program in C# that needs to monitor the amount of internet bandwidth currently in use so it can do a background upload when the internet usage is low. How can I automatically determine which network adapter is the one connected to the internet?

Babiche

Check this question https://mcmap.net/q/759672/-how-to-get-internet-ip/… – Bunton

More than one adapter might be connected to the internet. (For example, a wired and wireless connection on the same machine.) – Squeaky

Answer 1

I ended up following a link to MSDN when I was reading this page where I found the GetBestInterface function. I was able to use that to find the adapter thats connected to the internet

Babiche

Answer 2

You can use WMI to query all the adapters and see which one is connected.
This article shows you how to do it in VB.Net (very easily transferable to C#).

Hoarse

Answer 3

See here for a similar question on how to monitor the bandwidth used, in VB.NET, but the philosophy is the same! Here is another question that is the fastest way of checking for internet connection.

Hope this helps, Best regards, Tom.

Zamudio

Answer 4

Examine the routing table and look for the interfaces that have a default route (a route to 0.0.0.0) - that's your interface(s) that are connected to the wider world (if any).

Cinematograph

Answer 5

There are any number of ways an adapter may show as "connected to the internet" when it isn't. Conversely, it's possible for it to "not be connected to the internet" and still be connected.

Like many things in life, "The proof of the pudding is in the eating" If you want to know if you're connected, you'll need to try to talk to something.

I like time.gov since it returns a tiny chunk of XML containing the current time so you can make sure you're actually connecting to the net and not getting some sort of cached data or a redirect to a captive portal.

Just loop through the adapters and see which actually has connectivity.

Constringent

Answer 6

use below code snippet for get the current active network adapter.

using System.Net.NetworkInformation;
using System.Linq;

class Program
{
     static void Main(string[] args)
     {
        NetworkInterface networkInterface = NetworkInterface.GetAllNetworkInterfaces().FirstOrDefault(o => o.OperationalStatus == OperationalStatus.Up && o.NetworkInterfaceType != NetworkInterfaceType.Tunnel && o.NetworkInterfaceType != NetworkInterfaceType.Loopback);
        if (networkInterface != null)
        {
            Console.WriteLine(networkInterface.Name);
        }
     }
}

Rattling

You will get a virtual network interface if your machine has installed VMware or Hyper-V. – Relevance

Answer 7

There's another trick that will often work: Since virtual addresses are usually used by virtualization software where the PC is the host, the virtual interface has a gateway address. That means the v4 IP of a virtual interface will end with .1, or more precisely it is the lowest address within the subnet mask of that interface. So <IP> and (not MASK) will be 1.

There's no official rule that the gateway address needs to be 1, but it's a widely used standard.

Uncomfortable