I just found an issue with my MTU over a corporate router connecting from my home office back to corporae, with a VPN tunnel nailed up.

I hadn't though about MTU settings in a long time, but was having terrible performance when connecting over the corporate encrypted link.

Root cause I needed to reduce the MTU setting from 1500 to 1300 to avoid any segmentation. 

It would be a far greater experience if Windows would perform a Path MTU, and attempt to determine what the MTU is for a given interface, and set it automatically.

This applicable only to ipv4 as v6 has this functionality built into the protocol.

Chatting with my friends, only one who is also a Networking Expert would ever have realized there was a configuration problem, let alone be able to get to root cause, and fix it.

At a bare minimum if it can't be totally automated, at least flag the issue if packets are being dropped or segmented, and suggest an automatic MTU setting change.

• Moved by Paul E LongMicrosoft employee Tuesday, May 27, 2014 3:25 PM

Hi

How's everything going?

I haven't found a way to automatically set the MTU upon interface connection, but you can manually find an appropriate MTU for you neteork connection.

Please refer to this link for detailed information:
http://www.sevenforums.com/tutorials/94721-mtu-limit-test-change-your-connection-s-mtu-limit.html

Or use registry to edit the setting
1. run REGEDIT.exe
2. Go to : HKLM\System\CurrentControlSet\Services\Tcpip\Parameters\Interfaces
3. Select the Interface what do you want to config  example interface value: {111112-3344545-666666-777777}
4. Rich Click on Right Side and create a new RegWord type with:

name: MTU
value: 1300
base: Decimal
or  value: 514
base: Hexadecimal

5. Restart the System

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