Solution: Google and other "small" sites will load, but most websites won't load. "Only Google works."

I love comments, but I had to add this due to some of the ones this article has received: please don’t leave comments that complain about this not working and asking for help; if it doesn’t work, your problem isn’t THIS problem, and you need to do good old fashioned network troubleshooting, which is beyond the scope of this article or my generous unpaid assistance.

To make a long story short, I just finished fishing out a problem where a Vista laptop was connected via wireless and the only website that seemed to work was Google.  That is, until I tried another page I have that’s just a one-line message.

WARNING/UPDATE: This solution is not guaranteed to work, and should only be attempted if there is functional network connectivity but issues only arise when attempting to load items larger than about 1500 bytes in size. The default MTU for Ethernet devices is 1500, and modern operating systems use path MTU discovery to auto-correct this value if the MTU is too high. If your MTU needs to be smaller, it should be corrected at the router or modem, not the computer. However, in a pinch, this solution does sometimes work. If it gets worse, then the MTU may need to be even smaller; try 1480, or even 576. Be aware that smaller MTUs can cause slower connectivity.

Details: The laptop won’t load anything but Google.  Attempts to load other pages such as MSN, Yahoo!, etc. all fail.  The status bar says it’s “transferring data from http://www.yahoo.com”; but the Yahoo! page won’t load.  It looks like it’s “stuck.”

Checked everything security-related, dumped every security application just to be safe, but no dice.

Getting into the networking mess of things, I can ping google.com, but I can also ping every other site I try.  DNS servers are correct and DNS name resolution works beautifully.  There’s absolutely NOTHING wrong with the apparent network configuration, and no other computers or devices on the Internet through this router have the same issue.

So, because it’s obvious that everything is set up just fine, I took a shot in the dark and loaded a page I knew was very, very short and small.  This is how I test for MTU (maximum transmission unit) issues, where the largest packet size that can be transmitted across the wire (usually 1500 bytes in size) is set too high, and packets that are too large are simply dropped without notice.  Loading small pages or pages made up of many very small files, but failing to load larger pages, is a blatantly obvious sign of an MTU problem.

So, I had to tap into my command-line-fu and change Vista’s MTU for the wireless connection to see if things would get better, and they did.  Why there was an MTU issue, I may never know, and honestly there should never have been one in the first place…but there was.  Bottom line is this:  if small pages work and large pages don’t, change the MTU on the network interface using a command such as the following one, and the problem will be solved (hit start, type “cmd” in the search bar, hit control+shift+enter, say “continue” if prompted, type the command below and hit enter again):

netsh interface ipv4 set subinterface “Wireless Network Connection” mtu=1492 store=persistent

Replace “Wireless Network Connection” with the exact name of your wireless network adapter in the “manage network connections” part of the Network and Sharing Center.

About these ads