Wsrtjtyk

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

But that solution (set both mtu sizes to the same value), doesn't help in my case.

There exists a problem in GetIPv4Properties(), if the mtu sizes for ipv4 and ipv6 are set differently, then...

If ipv6 is enabled, both (GetIPv4Properties/GetIPv6Properties) return the mtu size of ipv6!

The Mtu value is only correct if the ipv6 protocol is disabled.

using System.Net.NetworkInformation;

foreach (NetworkInterface ni in NetworkInterface.GetAllNetworkInterfaces())

{

    if (ni.Name == "Local Area Connection")

    {

        Console.WriteLine(ni.GetIPProperties().GetIPv4Properties().Mtu);

        Console.WriteLine(ni.GetIPProperties().GetIPv6Properties().Mtu);

    }

}

But the correct values are shown by netsh

netsh interface ipv4 show subinterface "Local Area Connection"

netsh interface ipv6 show subinterface "Local Area Connection"

Without protocol version, the value for ipv4 is shown.

netsh interface ip show subinterface "Local Area Connection"

In my case, I need to check the mtu size for ipv4 independent of the ipv6 protocol enabled or disabled state.

Because my SW only works, if the mtu size is set to 1500 and I want to warn the user otherwise.

Is it possible with the NetworkInterface class or should I use a nasty hack, like

Process process = Process.Start(new ProcessStartInfo("netsh.exe", "interface ipv4 show subinterface "Local Area Connection"") {

                UseShellExecute = false,

                RedirectStandardOutput = true

            });

string output = process.StandardOutput.ReadToEnd();

process.WaitForExit();

Console.WriteLine(output);

@EDIT:

After the comments from @RonMaupin

There is no difference in MTU for IPv4 or IPv6, which are layer-3
protocols. The MTU is the maximum payload size of the layer-2
protocol, e.g. ethernet

That is correct, but for windows each protocol uses it's own mtu size and fragmentation.

Tested with mtu ipv4=1300 vs ipv6=1500 and ping of 1400 bytes:

netsh interface ipv4 set subinterface "Local Area Connection" mtu=1300 store=persistent

netsh interface ipv6 set subinterface "Local Area Connection" mtu=1500 store=persistent



ping6 -c 5 ff02::1:3 -s 1400

112 28.860467 fe80::64aa:56e9:fb1e:2081 ff02::1:3 ICMPv6 1462 Echo
(ping) request id=0x3160, seq=2, hop limit=1 (multicast)

ping 192.168.101.11 -s 1400 

152 102.027390 192.168.101.223 192.168.101.11 IPv4 1314 Fragmented IP
protocol (proto=ICMP 1, off=0, ID=2712)

153 102.027409 192.168.101.223 192.168.101.11 ICMP 162 Echo (ping)
request id=0x3450, seq=0/0, ttl=128 (no response found!)