I brought home a new (to me) 2012 macbook air to replace my 2010 MBA. I had the other macbook air on the network uploading some files to iCloud. As soon as I booted the new MBA up the whole network crashed. (Devices were still connecting to the Airport Extreme ac router, green light, but no internets). Restarting the router helped only briefly before the problem returned. When I was logging in with the new MBA I'd seen an error that there were two Macbook Airs on the network and that it was changing the name of one of them. I read somewheres that large upload traffic and lots of devices sometimes overwhelms the airport extreme (huh? not very extreme), so I went around turning off the wireless on iPad, Apple TV, and the old MBA. That, plus rebooting the router and the modem, seemed to do the trick for a time, until it didn't anymore. I've been reading around about DiscoveryD and problems with Bonjour. Will try that angle when I get home. Any other ideas???