Two possible scenarios:
- You are using VPN, but some of your applications time out (MTU is too big)
- Your OS is preconfigured for VPN by your employer, but the transfer rate can be better (MTU is too small)
In both cases the MTU needs to be adjusted:
- Start regedit
- Check all interfaces under HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces and find the one with the IP corresponding to the problem interface (e.g. the VPN tunnel interface). For example:IPAddress REG_MULTI_SZ 192.168.12.1
MTU REG_DWORD 0x000005DC (1500)As you can see the MTU is set to 1500 what is too high for a VPN tunnel
- Double click on MTU
- Click on Decimal
- Enter 1400 (or 1300 to be on the safe side, or 1500 if you are not using VPN)
- Click OK
- Reconnect (if you are connected to the VPN)
Also see:
Windows 2000/XP Registry Tweaks
How to change the PPPoE MTU size in Windows XP
Change the Maximum Transmission Unit (MTU) Size (Windows NT/2000/XP)