I recently dealt with a VPN problem which used a Linksys router and the client software called Linksys QuickVPN.
When using a DSL line with this software you will get a lot of drops and packet loss.
The Problem:
The VPN created by Linksys doesn’t account for overhead. If you are receiving network drops and data loss while connected by the Linksys QuickVPN you might need to try to adjust your MTU.
When Microsoft creates a VPN it accounts for the overhead and adjust the MTU from 1500 to 1400. Linksys claims that the software is built on top of the Microsoft’s VPN technology. I’m not sure about all that, but what I’m sure of is that you must adjust your MTU to account the overhead that Linksys does not.
Solution:
You will need to find your optimal MTU.
MTU Optimal Test
A series of ping tests using the command, ping www.google.com -f -l xxxx, where xxxx is the packet size, can be used to determine the optimal MTU for your connection.
- Go to Start and select Run.
- Type in cmd and hit Enter.
- At the DOS prompt, type in ping www.google.com -f -l 1492 and hit the Enter key.
Note the results above indicate that the packet needs to be fragmented. Lower the size the packet in increments of +/-10 (e.g. 1472, 1462, 1440, 1400) until you have a packet size that does not fragment.
If you have any packet loss, keep bringing the size down until you have 0% loss.
After you find your optimal MTU you will need to set it for your computer. There is two ways to do this.
The easiest way to change the MTU for your system is using DrTCP.
There is a hard way to do this, which involves changing the registry.
That dangerous information can be found here.
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