There are times when it is necessary to set the MTU size on a PC to a lower value than the default, in order to successfully use Client-Site VPN.
The encryption header of the VPN will take up space in an Ethernet data packet, leaving less room for actual data. You may find that small files will transfer across a VPN, but not larger files, because of fragmentation issues. In this case, lowering the MTU value on the PC to something around 1350 (your situation may require larger or smaller values) can get things working. You should experiment. You may also need to set the MTU size down on any target servers inside the LAN, though you should not need to adjust anything on a BorderManager VPN server.
MTU size is a registry value specification in Windows. The following programs can be used to easily set the MTU value. You will have to reboot for a new MTU value to take effect.
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