Warning: These setting affect all packets sent to all destinations and performance can severly be affected.

This is registry modification to hardcode specific MTU sices on a particular network interface:

 

Click Start, click Run, type regedit, and then click OK.

Locate the following key in the registry:

HKEY_LOCAL_MACHINESYSTEMCurrentControlSet

ServicesTcpipParametersInterfaces

On the Edit menu, point to New, and then click DWORD Value. Type MTU, and then press ENTER.

On the Edit menu, click Modify. In the Value data box, type the value of the MTU size, and then click OK.

Restart the computer