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[Current version of WinGate VPN is 2.5.1 - released December 22, 2008]
| MTU Issues |
An issue can sometimes arise within WinGate VPN where although machines and network shares are visible and users can connect, they are unable browse large directories or transfer files. This is can often be caused by MTU issues.
MTU (Maximum Transmission Unit) is the largest size of an Ethernet packet (data packet) that can be sent across a point to point connection, and if you are experiencing the types of issues outlined above then loss of these packets (due to their size) can often be the cause.
By using the Ping utility from the command line you can establish the size of the MTU that will work until packets begin to be lost.
You can test the size of the MTU and largest packet allowable by using the Ping command in conjunction with the "-l" (lower case L) switch followed by the packet size in bytes.
Usually the MTU is set to 1500 bytes by default so it is best to start with a figure around 1300 and work upwards. In most MTU test scenarios it is recommended that the –f (don’t fragment packet) switch is used as in most cases the connection will attempt to fragment packets that are larger then the MTU.
However WinGate VPN will attempt to fragment the packets anyway so it is not needed. The aim of this particular test will be is to see that even after fragmentation, what are the largest packets that WinGate VPN can handle before packets are lost.
To do this:
- Initiate a WinGate VPN connection.
- On the machine joining the VPN open up a command prompt.
- From the command line type ping (Ip address of the Host VPN machine) –l 1300.
- e.g . Ping 192.168.4.55 –l 1300
This will send a ping packet to the Host VPN machine with a packet size of 1300.
With a successful reply you should see a response like:
Reply from 192.168.4.55 bytes 1300 time <10ms TTL=128
Reply from 192.168.4.55 bytes 1300 time <10ms TTL=128
Reply from 192.168.4.55 bytes 1300 time <10ms TTL=128
Ping statistics for 192.168.4.55 :
Packets: Sent = 4 Received = 4, Lost = 0 <0%%loss>
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms
The purpose of determining the MTU size is to see what is the safest size of a data packet the WinGate VPN can send without it being lost.
Once this appropriate packet size has been established, then the MTU setting on the network interface will need to be changed.
Network Interfaces will often allow you to set the MTU through the registry or alternatively there is third party software available that will provide a GUI that will let you change the MTU in an easy and safe manner.
However, if a registry edit needs to be made, the most common place to set these:
Please note:
The following instructions involve editing the registry. You should only edit the registry if you understand the function and consequence of editing the registry and have taken the appropriate steps to backup the registry before proceeding.
On NT4 this located at:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
\Parameters\Tcpip
On Window 2000 and above:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
\Tcpip\Parameters\Interfaces\adapterID
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