I’ve hit across this problem a couple of times and always end up having to look up the magic incantations, so I’m going to store it here for posterity and in the hopes it may also aid other people.

Problem: Windows Vista / XP machine on a wireless network behaving extremely oddly. You can often browse to Google, for example, but basically nowhere else – it’s like other websites just time out.

Issue: For some reason, the MTU discovery doesn’t seem to work – the OS ends up sending packets which are too big and things stop working. This is probably an issue with one of the wireless routers involved I would imagine, rather than windows itself.


You’ll need an Administrator shell. Find the ‘Command Prompt’ in the Start Menu, and right-click to select ‘Run as Administrator’. Then, use this command to find the name of the interfaces on the machine:

netsh interface ipv4 show subinterfaces

Using the name we found above, do:

netsh interface ipv4 set subinterface "Name We Just Found In Quotes" mtu=1400 store=persistent

It’s a complete hack, but it works, and since I use Windows about once a year I really don’t care 😀