How to get the current MTU of an interface in C#

Question

I want to show the current network interface mtu value to the user. The user can change the mtu by the netsh command e.g. for the interface with id 11:

netsh interface ipv4 set subinterface 11 mtu=1700 store=persistent

How can I read the current MTU of an interface by the id or interface name?

If I use the NetworkInterface class example from the System.Net.NetworkInformation namespace all interfaces have an MTU of 1500. But with the netsh command (see above) I get the correct MTU values of e.g. 1700.

---

This is the example:

https://msdn.microsoft.com/en-us/library/system.net.networkinformation.networkinterface(v=vs.110).aspx

public static void ShowNetworkInterfaces()
{
    IPGlobalProperties computerProperties = IPGlobalProperties.GetIPGlobalProperties();
    NetworkInterface[] nics = NetworkInterface.GetAllNetworkInterfaces();
    Console.WriteLine("Interface information for {0}.{1}     ",
            computerProperties.HostName, computerProperties.DomainName);
    if (nics == null || nics.Length < 1)
    {
        Console.WriteLine("  No network interfaces found.");
        return;
    }

    Console.WriteLine("  Number of interfaces .................... : {0}", nics.Length);
    foreach (NetworkInterface adapter in nics)
    {
        IPInterfaceProperties properties = adapter.GetIPProperties();
        Console.WriteLine();
        Console.WriteLine(adapter.Description);
        Console.WriteLine(String.Empty.PadLeft(adapter.Description.Length,'='));
        Console.WriteLine("  Interface type .......................... : {0}", adapter.NetworkInterfaceType);
        Console.WriteLine("  Physical Address ........................ : {0}", 
                   adapter.GetPhysicalAddress().ToString());
        Console.WriteLine("  Operational status ...................... : {0}", 
            adapter.OperationalStatus);
        string versions ="";

        // Create a display string for the supported IP versions.
        if (adapter.Supports(NetworkInterfaceComponent.IPv4))
        {
             versions = "IPv4";
         }
        if (adapter.Supports(NetworkInterfaceComponent.IPv6))
        {
            if (versions.Length > 0)
            {
                versions += " ";
             }
            versions += "IPv6";
        }
        Console.WriteLine("  IP version .............................. : {0}", versions);
        ShowIPAddresses(properties);

        // The following information is not useful for loopback adapters.
        if (adapter.NetworkInterfaceType == NetworkInterfaceType.Loopback)
        {
            continue;
        }
        Console.WriteLine("  DNS suffix .............................. : {0}", 
            properties.DnsSuffix);

        string label;
        if (adapter.Supports(NetworkInterfaceComponent.IPv4))
        {
            IPv4InterfaceProperties ipv4 = properties.GetIPv4Properties();
            Console.WriteLine("  MTU...................................... : {0}", ipv4.Mtu);
            if (ipv4.UsesWins)
            {

                IPAddressCollection winsServers = properties.WinsServersAddresses;
                if (winsServers.Count > 0)
                {
                    label = "  WINS Servers ............................ :";
                    ShowIPAddresses(label, winsServers);
                }
            }
        }

        Console.WriteLine("  DNS enabled ............................. : {0}", 
            properties.IsDnsEnabled);
        Console.WriteLine("  Dynamically configured DNS .............. : {0}", 
            properties.IsDynamicDnsEnabled);
        Console.WriteLine("  Receive Only ............................ : {0}", 
            adapter.IsReceiveOnly);
        Console.WriteLine("  Multicast ............................... : {0}", 
            adapter.SupportsMulticast);
        ShowInterfaceStatistics(adapter);

        Console.WriteLine();
    }

Answer 1

I've found the answer by myself. I have to change the MTU also for the ipv6 interface like:

netsh interface ipv4 set subinterface 11 mtu=1700 store=persistent

netsh interface ipv6 set subinterface 11 mtu=1700 store=persistent