CODEWITHSUNDEEP
c#network-programming
user109793
user109793

Reputation:

How can I tell if a network cable has been unplugged?

I have a C# application that should only be used when the network is down, but am afraid users will just unplug the network cable in order to use it.

Is there a way to detect if the network cable has been unplugged?

Thanks

Upvotes: 6

Views: 8620

Answers (9)

Dinesh Kumar P
Dinesh Kumar P

Reputation: 1168

To detect 'Is network cable plugged in a machine?', below piece of code works. 

class Program
{
    private static void Main(string[] args)
    {
        bool isNetworkCableConnected = System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable();
    } 
}

Upvotes: 0

EyuelDK
EyuelDK

Reputation: 3189

You could register a delegate to the NetworkChange Class. When a network change occurs, it doesn't actually notify you what happened, so you could list all the network interfaces (Using NetworkInterface), filter the ones that concern you (By checking there properties) and check their operational status.

Upvotes: 1

Ananth
Ananth

Reputation: 31

You can use this 

System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable()

Upvotes: 3

Harry Lime
Harry Lime

Reputation: 29576

How about pinging the default gateway?

There is some code here that gets the default gateway from the registry.

Upvotes: 0

Jeff Mc
Jeff Mc

Reputation: 3793

You could use IsNetworkAlive(). Although technically it doesn't check link state, it's probably better since it can detect wireless and dialup connectivity as well. Here's an example:

using System.Runtime.InteropServices;
class Program
{
    [DllImport("sensapi.dll")]
    static extern bool IsNetworkAlive(out int flags);

    static void Main(string[] args)
    {
        int flags;
        bool connected = IsNetworkAlive(out flags);

    }
}

The flags param returns whether the connection is to the internet or just a LAN. I'm not 100% sure how it knows, but I'd bet it just looks to see if there is a default gateway set.

Upvotes: 6

Alex Angas
Alex Angas

Reputation: 60017

Some network drivers are able to detect this. However you'd need to use unmanaged code to access them from C# (which may be very difficult/impossible) and the solution may not be reliable for all network adapters.

Upvotes: 2

mouviciel
mouviciel

Reputation: 67831

In my humble opinion, there is no certain way to distinguish between a network down and an unplugged cable. And even if there is a way, there is also a way to work around it.

Let's assume that you have a solution and let's look at some situations:

  • There is no network traffic, the cable is not unplugged from the computer: it may be unplugged at the other end.
  • There is no network traffic, the cable is unplugged: but this has always been the case, the laptop is connected via Wi-Fi, which is down at the moment.
  • There are several network interfaces, only the one connected to WAN is down: should your app work?
  • The network is actually down, in the sense you mean: someone has managed to reboot the router continuously for using your app.

Upvotes: 4

Martijn
Martijn

Reputation: 6763

If I really wanted to use your application and whether it will work depends on something like this, I would always be able to find a way to trick your application. Are you sure there's no better solution?

Upvotes: 0

Aaron Digulla
Aaron Digulla

Reputation: 328556

The network card will report this as a state. Tools like ethtool can display this (Link up), but that is only available for Linux/Unix.

If you can enumerate the installed network cards with a Windows API, I'm sure you'll find the flag for "link up" somewhere in there.

Upvotes: 1

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