[Solved] Connection reset on some but not all sites.

3 min read
Key terms: connection reset, traceroute, tracert, connection timed out, wifi, router, 3G, anonymous browsing, MTU, packet size, ping

Symptoms:

  • For some but not all websites you get the error message ERR_CONNECTION_RESET in Chrome or The connection was reset in Firefox
  • This is a problem on all connections via your router ie using wifi on this line gives you the error but if you connect, say, via 3G, there is no problem
  • Running a traceroute test is OK
If the solution proposed below is too technical or scary, skip to the bottom of the page for a simple – but temporary – workaround.

 

Diagnostics and Solution

First lets confirm the situation by running a …
Traceroute Test (Windows)

  1. Click the Start button and select Run.
  2. Enter cmd into the Open field
  3. Type tracert www.domain.name

See: https://sg.godaddy.com/help/performing-a-traceroute-in-mac-os-x-3366 for running the test on Mac.

If you get the message “trace complete” without any “request timeout” messages THEN THERE IS A GOOD CHANCE your problem is that the PACKET SIZE of the data is too large for the route. The traceroute sends tiny packets of data… your web browsers sends much larger packets. It’s these fat browser packets not getting through.

MTU = Maximum Transmission Unit
A successful trace:

MTU Test
OK so lets figure out what is the maximum package size that will work for your route.

Stay in the windows dialog to test the following:

  • ping -f -l nnn domain.name

where nnn is the MTU to be tested. Start at 1504.

Example: ping -f -l 1504 www.fonts.com

You may get a message like Packet needs to be fragmented but DF set.

Now run the test again dropping nnn by 32 until the ping works. I found that I could not access the destination site with a setting of 1472 but I could with 1440.


Resetting MTU

You will find instructions here: http://support.microsoft.com/kb/826159

You have the options of running a little fix-it app (I used it, it’s very straightforward) or hacking the registry yourself.

THEN REBOOT.
Resetting MTU on a Router

You may need to change the setting for your router especially if you run off a wifi and everyone is experiencing the same problems through that wifi.

You can usually acccess your router via the IP address 192.168.1.1. Look for the MTU Size, set it to Manual and the necessary packet size.

Look up the instructions for your brand of router.

Why oh why
I’m glad to say this solved a problem that had been plaguing me for a week. I have no idea why it spontaneously became an issue as it seems none of my own settings have changed. Could it be that a key router along the path to these destination sites had its settings changed? If so, a number of people in my area are likely affected. I guess we’ll never know.

 

A temporary workaround: Anonymous Browsing

If the whole idea of getting this geeky puts you off, there is an easy way to “glimpse” at a page by bypassing the usual route giving your problems, and that is via an anonymous browser.

Just view the website giving you problems by entering your URL here:
http://anonymouse.org/anonwww.html

This basically gets to the same webpage via Anonymouse so you should not have the same route contraints causing you the reset error. It is very tedious to keep doing this but for a quick fix, this will do the job.