Wi-Fi network cannot be joined in El Capitan (or Yosemite)

Discussion in 'OS X El Capitan (10.11)' started by d_gomaiste, Mar 18, 2016.

  1. d_gomaiste macrumors member

    Mar 18, 2016
    Hey all —

    For a few months now, I've been unable to connect to my home Wi-Fi network on my late-2012 iMac. It started out of nowhere with Yosemite 10.10.5 — everything had been running smoothly since I updated in late 2014, but suddenly stopped a few months ago. My Wi-Fi network will occasionally show up in the list of networks, but any time I try to join, I get the "cannot be joined" error.

    Today, I finally upgraded to El Capitan 10.11.3 hoping it would resolve the issue, but to no avail.

    All other devices in the house (a MacBook Air, a Windows laptop, and three iPhones) can connect without issue. My iPhone and MacBook Air can both connect in the same room as my iMac, and the MacBook is still running 10.10.2. Clearly, this is a problem with my iMac and NOT the router (I even changed service providers last week). I've tried all of the usual suggestions:

    - Deleting network prefs in Library/Preferences/SystemConfiguration, then rebooting
    - Renewing DHCP lease
    - Resetting PRAM
    - Adding a new network location and using Google DNS
    - Turning off Firewall
    - Disabling AWDL
    - Disabling Bluetooth
    - Rearranging service order in Network Preferences
    - Turning off Wi-Fi and Bluetooth on my iPhone 6 (iOS 9.3 beta)

    I have the following peripherals: USB mouse, Bluetooth keyboard + Magic Trackpad, UAD Apollo Twin Solo, Native Instruments Maschine Mikro, and 2 external HDs.

    I've had to resort to using my phone's hotspot to get work done, but now, it seems the Wi-Fi Hotspot and the Instant Hotspot no longer work and I have to use Bluetooth. Obviously, this is not viable long term.

    A clean install would be a last ditch effort. The only Time Machine backup I have is one I made last night before updating to El Capitan. If it comes down to it, I wouldn't be opposed to backing up my /home folder, reverting to Mavericks, and reinstalling everything manually... I'd like to avoid this, of course.

    Any advice or suggestions welcome. Thanks so much!!
  2. graley macrumors regular

    May 25, 2010
    --- Post Merged, Mar 19, 2016 ---
    Switch off the power to the router..wait
    Turn power back on....wait.
  3. rigormortis, Mar 19, 2016
    Last edited: Mar 19, 2016

    rigormortis macrumors 68000


    Jun 11, 2009
    there are two things you can try to solve this.

    1) forget the wifi password. use the preshared key instead. to do this you ether can go and use airport utility and click on show passwords. it will give you the correct preshared keys for your wifi connection. use these preshared keys instead of your wifi passphrase. you can copy and paste these. if you don't have an airport extreme then you can go to the wireshark psk generator @ https://www.wireshark.org/tools/wpa-psk.html - sometimes with wifi devices, like the amazon kindle keyboard .. it calculates the wrong pre shared key and cannot connect to your network

    remember that it is the pre shared key that is used to connect to your wifi network. your regular wifi password is just part of the mathematical equation that is transformed into this 504 bit key

    2) the most common reason that you would get ' unable to join network ' is because your multicast setting is set to high. back in the 802.11g days you used multicast to prevent wifi clients that are farther away from connecting to your wifi. try setting multicast to low. you need 5.6 of airport utility for windows to set this.

    the problem with 802.11g was that if a client connected to your wifi at 1 mbit , then all clients connected at 1 mbit. so you prevented this by setting multicast to high. this was fixed in 802.11n and 802.11ac , they incorporate MIMO which allows all clients to connect at their native speeds

    if neither #1 or # 2 solves your problem. maybe you have a bad wifi card, and you should have the genius bar replace it
  4. d_gomaiste thread starter macrumors member

    Mar 18, 2016
    Hey, thanks so much for the reply! I'll give each of these a try when I get home tomorrow afternoon.

    Quick question — could you explain why I need the Windows version of the Airport Utility, and why version 5.6? The Apple download page says 5.6 is for OS X Lion. Also, my new router is a Dual Band Wi-Fi 802.11ac — do you think the low multicast fix would be compatible with this unit?

    Just wanted to be sure. Thanks again for your help!!

  5. rigormortis macrumors 68000


    Jun 11, 2009
    the older version of airport utility ( windows ) offers extended logs and features that were removed from the current version. this made airport utility more stream lined. and less complicated. the ability to adjust multicast is now impossible in the current version.

    the old version allowed you to look up the entire dns list of network devices, wired and wireless. which cant be done in the newer version. the old version would show you the actual speeds of those wireless clients, which is mot in the new version, the old version allowed you to view logs, which are not in the new version

    airport utility should only be used on actual apple airport basestations. if your dual band router isn't made by apple , then you don't need airport utility at all
  6. jrazor macrumors newbie


    Apr 3, 2016
    Rancho Cucamoga, CA
    Did any of the above suggestions resolve your issues?

    I have notice that on several of the MP's through our shop that we would need to have the OSX forget the "network" that we were trying to connect to and just start over from scratch.
    Not sure why but it has worked for us.
  7. d_gomaiste thread starter macrumors member

    Mar 18, 2016
    Unfortunately, the above suggestions didn't work. How are you making OS X "forget" the network? I've tried removing it in the Network section of System Preferences, but to no avail. :(

    Thanks for your help!
  8. tom123 macrumors regular


    Apr 9, 2006

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