1) Check the problem client's MTU value for its Local Area Connection interface:
In an elevated command prompt type:
netsh interface ipv4 show interfaces
Here is an example output showing the Local area Connection is using 1300 as MTU value:
Idx Met MTU State Name
--- ---------- ---------- ------------ ---------------------------
1 50 4294967295 connected Loopback Pseudo-Interface 1
12 5 1300 disconnected Local Area Connection
2) Run the same command on the NVBU server and some working clients to compare the values.
The default value being 1500 it is very likely all other machines will be using 1500.
3) If the problem client is the only one on a different MTU setting, change the problem client MTU parameter to the same MTU value as all other working clients:
Example:
In an elevated command prompt on the problem client type:
netsh interface ipv4 set subinterface "12" mtu=1500 store=persistent
Note the 'subinterface "12" ' being the Index number returned in step 1.
You can also use the name of the interface instead:
netsh interface ipv4 set subinterface "Local Area Connection" mtu=1500 store=persistent
4) Reboot the server and verify the MTU is now the same as all other NVBU machine on the network.
If after reboot, the MTU value returns to the value causing problems, the MTU will have to be set manually in the registry.
The MTU setting is determined by Windows by negotiating with the low level drivers for each of the NICs.
If reboot resets MTU to the problematic value, then this issue is driver or hardware related.
You can set the MTU manually in the registry as described on Method 3 in this Microsoft KB:
https://support.microsoft.com/en-gb/kb/900926
Please ignore Method 1 and 2 on this link and only apply:
Method 3: Set the MTU size for the network interface manually
This Microsoft KB does not elaborate on how to find the correct ID for the local area interface:
<ID for network interface>
When you get to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\
you will see folders with numbers.
Each corresponds to an interface on your machine.
Here we want to set MTU for Local Area Connection.
To know which of the folders is for Local Area Connection, click on each of the folders and look on the right pane to identify the correct one using the DhcpIpAddress parameter.
The folder with the Local Area connection IP address is the one where to create the MTU DWORD value described by Microsoft.
You should reboot the server after this to see if it resolves the issue.
If MTU goes back to the prpblematic value even after manually setting it in the registry to override the preferred MTU for this NIC, then the issue should be escalated to Microsoft Support or the NIC driver should be upgraded, or the NIC changed to comply with today's widely used default network settings.
