A network support customer with DSL had lost Internet access over the weekend.  They tried rebooting the DSL modem and Linksys WRT54G router to no avail.  When I got onsite, I connected to the router’s wireless as well as Ethernet port with my laptop and confirmed that there was no Internet access.  I connected to the web management interface of the router which had a complex password, so the customer likely had not gone in and changed anything. 

I could see that the router had successfully obtained a public IP address, gateway, and DNS servers from the ISP.  There was an internal ping utility built into the router, and I was able to use it to successfully ping the DNS servers and gateway IP addresses.  When I tried from the connected PC, I could ping the router’s public interface, but not the gateway of the router or the DNS servers. 

I looked through the settings to see if I could find any reason that traffic was dying going through the router and could not find anything.  I then backed up the configuration of the router to my laptop and did a factory reset.  After the router came back up, I was able to access the Internet through the router and ping everything.  [more]

I uploaded the configuration file back on to the router and it broke the connection again.  I decided at this point to factory reset again and manually set the password and SID on the unit back to the previous settings.  It is my guess at this time that the configuration on the router had become corrupted.