From time to time a Mac-owning friend will call for a spot of assistance and it's surprising what two minds can do to solve a problem. So, a couple of days ago an old friend living on a Greek island contacted me by Skype to complain that her brand new iMac appeared to “have lost the internet”. Since she was Skyping me with this news I felt entitled to scoff and suggested she was imagining the problem.
We spent an unproductive hour checking everything. What was happening was that Mail was in a total spin on all mailboxes, despite restarting the application several times. Even more worrying was that Safari continually reported that it was not connected to the internet. Reluctantly, after several reboots of the iMac, I had to agree that there was something strange afoot. Several other Mac fans she knows were consulted and failed to solve the issue. She had even been advised to delete one complete mail account which was a suspect. This turned out to be a mistake caused by too many geeks in the broth.
As a last resort I posted a question on the Apple Discussion Forum for OS X Snow Leopard. Almost immediately I got a reply from an expert on the topic who suggested a couple of things to try. First, he suggested we check whether there were any specified proxy servers in Network preferences. Then, to find out whether she could connect to her DNS server. While I was pondering this, the Skype dong donged and southern Crete reported that all was working when she looked at the computer after breakfast.
My helpful correspondent on the Apple forum immediately came up with what was clearly the answer to the conundrum:
"What very likely happened is that either your friend’s ISP’s DNS server(s) went down, or DNS service via their router went down. DNS is what is responsible for converting names such as “apple.com” to numeric IP addresses like “17.112.152.57.” So if DNS isn’t working properly, attempting to visit any site by name won’t work, but Skype will. Skype doesn't use DNS, as it has a numeric IP address hard coded into the application."
We all live and learn. And I'm posting this because it's a strange one (at least to me) and could help someone else in the future. What I suspect happened was that there was a power cut during the night, not an unusual event in southern Crete. That would have reset the router and, probably, the DNS server along with it. It is unlikely to have been an ISP fault simply because it had gone on for three days. Elementary my dear Jobs. And we are very fortunate in the Apple world to have so many experts dedicated to sorting out our every problem within hours.