Q: 10.10.3 Nuking My Network

ASUS RT-AC66U has some really bad issues. Check if you see a firmware update for this router. Their newer firmware has helped some folks. But otherwise you should probably consider getting a new router. This one has lots of reports of poor WiFi across the web.

Boot into recovery mode (hold cmd+R at startup). Connect to the network & see if Safari works via the 'Get help online' option. Do the other devices also get affected in when the laptop is in recovery mode?

Is it just wifi or is ethernet affected too?

When the other devices are affected is it just internet traffic that is slowed down ? e.g. does file sharing between 2 Macs work? You will need to enable file sharing to test this unless you have other services to test.

I had the exact same problem. If I turned on my iMac, the entire network would be unusable by anyone else in the house. I haven't bothered turning my iMac back on since it is old and rarely used. I just upgraded my brand new MacBook to 10.10.3 and while it doesn't lock up the network, it does slow it down quite a bit.

I would suggest going into the new "Photos" app and under "Preferences" click on the iCloud tab and if it is syncing your photo library press the "pause for one day" button and see if that alleviates it somewhat.

If the Photos app is syncing while anyone else is on the network, I will immediately get complaints from my wife and kids that the internet is not working. When I click "pause for one day", the speed picks up again.

Seems like this is getting some attention elsewhere…

http://sixcolors.com/post/2015/04/photos-for-macs-unrestrained-icloud-uploads/

I'd recommend you send feedback if you are sure this is the issue - Apple should prioritise if many people report the same issue…

http://www.apple.com/feedback/

To me, it definitely has something to do with the new Photos App.  Every time I downloaded an update to the 10.10.3 Beta (Macbook Pro mid-2009) everything seemed fine until I opened the Photos App; then my Macbook Pro would cause dropping of the internet (even purchased a new Time Capsule router because I thought maybe it was the "old" Time Capsule). The "wifi" connection stays but every device in our house cannot access the internet while the Macbook Pro is open because of the off/on, off/on of internet connection. I just downloaded the new official release of Yosemite 10.10.3 with Photos App hoping this issue was fixed before they released it.  I'm afraid that as soon as I open the Photos App, the dropping of internet will start again (not to mention the Macbook Pro slowing to a crawl).

Applesass,

You realise that the new Photos app will upload all your images to iCloud? That causes it to consume all outbound traffic making other devices have poor internet performance. Other devices cannot make requests when another device is sending lots of data - they have to wait their turn.

Open the Photo app preferences & pause the uploads - you will see if that is the only cause of the slowness.

It is explained at sixcolors…

http://sixcolors.com/post/2015/04/photos-for-macs-unrestrained-icloud-uploads/

Thanks, Drew, for all of the helpful info and link to Jason's website.

Sam-- Did you ever resolve this issue? I'm having the same problem, and it isn't related to Photos.

Thanks!