A DNS Problem and its Solution

On Wednesday afternoon Zoe and I got home to find that our connection to the web had stopped working. When we tried to go to a web-site such as www.google.com the browser would just sit there waiting for a minute or so before giving up. We couldn't think of anything we had done since the previous evening that could have caused the problem.

We have two computers that connect to the internet through a Zoom ADSL X5 modem router. The problem was common to both computers so the problem was either with the modem or with our broadband supplier. I opened up a MS-DOS window in Windows XP and tried to ping Google:

  ping www.google.com

Google replied. Then I pinged Google from a terminal window in Linux, with the same result. So, the underlying internet connection was working. The problem must therefore be with the DNS name lookup (the mechanism which converts URL's such as "www.google.com" into the 4-number network addresses such as "245.10.45.97"). I dug out the printout I kept of my broadband supplier's connection instructions (you should always have a copy of these, either as a printout or as a file on your PC because when something goes wrong you won't be able to get to their web-site!). What I needed were the addresses of primary and secondary domain name servers (DNS) which were 195.74.102.146 and 195.74.102.147. The Zoom ADSL modem router is configured using a web-browser interface.  I started Firefox, entered http://10.0.02 as the URL and pressed 'Go'.  I then logged into the modem router with the username and password which I have noted down from when I installed it.  Then I went to the DNS Setup page (its under Advanced Setup).  The existing DNS setup was 'Use Auto Discovered DNS servers only'.  I changed this to 'Auto Discovery + User Configured' and entered 195.74.102.146 and 195.74.102.147 as the Preferred and Alternative DNS servers.  I then saved the changes and wrote then to Flash.  The modem rebooted and then we could get through to Google (and the rest of the Web) again. 

I still don't know what caused the DNS lookup to fail when it did, but I don't care because I have got it working again and Zoe thinks I am a hero!