I have used the Buffalo WHR-G300N over 2 years while I will use it for connecting all of my devices to Internet @ home. However two days ago I have the issue that the router suddenly disconnected from the Internet -- all of my devices (wired and wireless Notebook, Mac Mini, iPhone x 2, iPod Touch, iPad, Nexus 7, Windows Phones x 2) cannot connect with the router. I have tried to turn router Off and On -- the internet connection was back to normal for several minutes.
I have the same problem using my Buffalo N600. No idea why after months of no trouble I can't connect.
I've power-cycled the whole network. I have no trouble seeing other machines on the network but can't get to Internet. I tried renewing DHCP leases and connecting from other machines. I can't get past the router.
When plugged directly into modem I can connect to Internet so I know that the ethernet cable and modem work.
UPDATE: While I still don't know what the problem was a call to Buffalo TEAM solved it: