From time to time (maybe every 2-4 hours) I recognize the same behaviour on my lan.
Sometimes it takes quite a long time (more than 10s) until a webpage shows up, sometimes I get the “page not found”. In this case from time to time webpage shows up after a reload, but usually not, then I need to wait a few minutes.
I never found out what causes this problem, I also couldn’t make sure if it is caused by the router (zs) or not.
When I check the network, zs router and internet connection, everything looks perfect, I just can’t open webpages. Connections that were already established, e.g. skype or vpn, still work.
As far as I remember I changed adress of dns server and it looks like it got better but still happens from time to time.
When I have a look to the logs in the time of failure, it looks like there isn’t even a new request to zs. But why should different browsers on different PCs have the same problem all at the same time?