My internet connection has been giving me grief for quite some time now. It seems my connection to the Spark DNS servers falls over on a fairly regular basis. Restarting the modem or resetting DNS settings fixes it.
I don't think it's the modem for two reasons.
1) It's happened on two modems
2) If I set the modem to use google's DNS servers, the problem goes away.
The problem resurfaced tonight after I set the modem back to automatic DNS a day or two ago.
My partner had no access using Spark DNS, I had no problem using Google. I changed my tablet back to automatic (Spark) and couldn't connect.
Changed the modem to google then back to auto, and we're away again.
The modem is a TP link TD-W8950N, the previous one was a linksys wag200g. When the DNS servers don't respond, the modem reports no problems.
I haven't tried pinging the servers when it's not working, I'll try that next time.