如何在C#中获取接口的当前MTU

Question

我希望向用户展示当前的网络接口mtu值。用户可以通过netsh命令更改mtu，例如针对id为11的接口：

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

我该如何通过 ID 或接口名称读取当前接口的 MTU 值？

如果我使用 System.Net.NetworkInformation 命名空间中的 NetworkInterface 类示例，则所有接口的 MTU 均为 1500。但是，使用 netsh 命令（参见上文）可以获得正确的 MTU 值，例如 1700。

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这是例子：

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();
    }

- Maddy

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“有效的MTU是所有网络组件中最低的MTU。当您尝试1700时，您会很快遇到这个问题，因为以太网帧只能携带1500字节，您无法绕过下一步的基本MTU限制。” - Hans Passant

Answer 1

我已经自己找到了答案，我需要像下面这样修改ipv6接口的MTU大小：

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

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

- Maddy

Answer 2

主要问题是一个问题的

NetworkInterface.GetIPProperties().GetIPv4Properties().Mtu
NetworkInterface.GetIPProperties().GetIPv6Properties().Mtu

如果启用了ipv6，则两者都返回ipv6的mtu大小！只有在禁用ipv6协议时，MTU值才是正确的。

但是，通过netsh显示的是正确的值。

netsh interface ipv4 show subinterface "Local Area Connection"
netsh interface ipv6 show subinterface "Local Area Connection"

没有协议版本，只显示ipv4的值。 netsh接口ip show subinterface "本地连接"

起初我以为，在启用ipv6的情况下，只使用ipv6-mtu大小，但事实并非如此。

- jeb