"There's no way this is a widespread problem in Yosemite. It's got to be something local to your machine. Try forgetting the router, delete the related preferences, create a new location, etc..."
Could you please not make assertions like that? I'm sure you're just trying to be helpful, but something clearly happened with the Yosemite upgrade. It doesn't mean the issue affects everyone; it could be the driver for a specific WiFi chip some of us are unlucky enough to be stuck with.
I am also affected by this problem.
This is what I have observed:
- If I shut down my MacBook, start it up without doing anything special with the network, then if I ping google I get a normal reply time.
- If I then put the network under a little load (specifically use curl to fetch the latest openssl tarball), the ping-time goes up fast, and pretty soon I start getting request timeouts. At this point the network is mostly useless.
- The breakage isn't complete though. If I keep pinging, I will eventually get a few packets which get through, albeit with very high delay. Some of the tarball downloads have actually run to completion, but rather than take the usual minute or so, it can keep trying for 15-20 minutes. Sometimes it times out and fails, but I'm getting some complete tarballs as well.
According to system_profiler I have:
Card Type: AirPort Extreme (0x14E4, 0xEF)
Firmware Version: Broadcom BCM43xx 1.0 (7.15.124.12.8)
..for some reason it thinks I'm in GB, which I'm not.
I have around 10 other devices (PC's, iMac, consoles, tablet, etc), some use wifi and some don't. Nothing else is on the network affected by the problem; it's only the MacBook which I just upgraded to Yosemite.
Could others who are having the same issue check what Card Type they have? Run system_profiler in the Terminal and look for the WiFi section (for me it's right at the bottom.. Beware that it takes a while to run to completion).