The Blog of Steve

MTU Settings under Vista

<p class="MsoNormal">I recently started using Vista Ultimate on my laptop. So far, I am very happy with its performance but there has been an ongoing issue that I have been experiencing with it while using it at uni.

This problem was that certain web sites or network resources would not load correctly over the wireless connection while at QUT (eg: pages like <a href="http://www.whirlpool.net.au/">www.whirlpool.net.au</a> would half load and then hang). It worked fine at home and on other wireless networks. I had seen similar problems at work and they were generally MTU related. The issue was however that the Vista uses path discovery to discover the required MTU settings.
I believe however something to do with the QUT network (possibly the use a transparent proxy ) was somehow stopping this from working correctly.
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<p class="MsoNormal">The reason why this issue has never manifested itself until now is because the installation of the Cisco VPN client forces the MTU of all network adapters to 1300 upon installation.

The issue that was then found was that Vista doesn't allow you to edit the registry in the same way as XP did. However, after a bit of searching on the net, I came across the following commands that will allow you to set MTU under vista.

<strong>To view the status of your network adapters
(ie: to view the MTU) you use the following command:

netsh interface ipv4 show subinterfaces

<strong>And to set the MTU of the desired interface:
(setting my wireless adapter to 1470 in this case, this max MTU was found by performing a ping with the do not fragment flag set and finding the max packet size, eg: ping -f -l 1470 www.qut.com)

<font color="#ff0000"><strong>The following was run in an a command prompt that was run as administrator.

netsh interface ipv4 set subinterface &quot;Wireless Network Connection&quot; mtu=1470 store=persistent

After setting this, I found that everything worked fine. Happy days..

Hope that this can be helpful.