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Mountain Lion has Wi-Fi Issues

What would a new OS launch be without a few hiccups?

I experienced a Wi-Fi issue on my 2008 iMac wherein Mountain Lion’s Wi-Fi connection gets really slow… dial-up slow. Restarting the modem and Airport router didn’t fix it. Only plugging in direct via ethernet fixed the issue.

I checked online and there’s only a smattering of posts with people discussing the issue. Either it’s not widespread or people haven’t noticed it yet.

One post in an Apple Discussion mentions that they took their laptop to an Apple Genius and they fixed it, but they couldn’t see what the genius did. Maybe Apple will issue an update in the future, or maybe there’s something quick an easy that fixes it.

We’ll look into it more and let you know if we come up with anything to fix this Wi-Fi slowdown issue with Mountain Lion.

If you have info on fixing, or are experiencing a similar issue leave a comment below.


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  • Check the settings of the firewall in the router; test with the laptop wired to the router with wireless disabled temporarily. Take the laptop to a friend and test again.

    • I have this same issue, it connects to the Network but I have no access to internet whatsoever. You say “Deleting /Library/Preferences/SystemConfiguration” works but where is that? How to I get in that? Would very much appreciate your help. Thank you!

  • HeYo.
    Had same prob as everyone else. Downloaded ml to mac air. No wifi a day later.
    Tried lots of options on this page but his WORKED FOR ME….
    System preferences
    + symbol, enter
    Save and close preferences

    Works ten seconds later.


    • I think this has worked for me. I have been having similar issues to this post, basically i can’t hang on to my wifi signal it is constantly dropping to the point that I had to use my phone as a data source yesterday to get any work done. I thought maybe there was a hardware issue since this computer is almost 4 years old, but your fix seems to have worked! So thanks!

    • worked briefly on 17″ MBP but next time I reconnected to Airport, same issue – (Big Mountain Lion GGGGRRRRRR – because none of our other MBPs have any problems with older OS)

      am trying deleting System Config file now….

      • Hey All – Back up your stuff and follow the directions to delete the System Configuration folder (below) – Worked Great. Thanks to the blog!

  • Hi guys, I had this problem too and I had tried everything but nothing worked for me so i decided to find out what’s wrong with this SOAB xD. What i did was… i went to router configuration setting and changed some settings under wifi setting. (it worked for me)

    First of all make sure you’re using a WPA2, for WPA-type use Phssphrase and chose your password. But make sure there are no numbers in in your network password.

    Second schange your channel. Before i had set it on channel 6 now i changed it on channel 11.

    Also make sure your Encryption is set on AES.

    i’m giving you also a picture of my Wifi-Settings down below.

    • Wow, April 2014 and still issues like this. I’m amazed that taking the numbers out of password fixed the slow webpage problem!!! (I didn’t do any of the other fancy stuff) Thanks!

  • Bizarre and expensive fix for me. Called Apple support and after running multiple tests on my day old MBA they suggested a return and replacement. Fair enough. Now how to get my data from my MBA (which had been migrated from a MBP which is now elsewhere) to the replacement due in a week and the “faulty” MBA being picked up in two days? Purchase a Time Capsule for the backup and to replace the Airport Extreme with the Airport Extreme to go back the office. Set up the Time Capsule with the Airport Extreme settings and bingo everything works 100%. Called Apple to cancel the return and replacement. So in my case there was something funky with my Airport Extreme and MBA which wasn’t there for our other 2 MBP’s and iMac which are still flawless.

  • Yet another 17″ 2012 Macbook Pro – upgraded to 10.8 and having bad time with the wireless at my work location. My Home location, where the wireless is served up by a 4th generation Time Capsule was OK though.

  • I have a 2012 MBP, an oldish Time Capsule and a fairly recent Airport Extreme running as one network – Before ML everything was fine and good speed, since the update the connection to the older Time Capsule is pretty unusable but in the room with the Airport Extreme speeds are as they were.

  • I talked with a Genius to figure out this problem and I think it may have solved the problem. This applies only to people who may have upgraded or migrated their data. The hypothesis is that the migrated network settings left some garbage that is affecting Mountain Lion. I’m only on day two after trying this and haven’t seen any issues yet, so it may be a final fix.

    What we did was the following:
    1. Quit out of all applications and save any work
    2. Delete your /Library/Preferences/SystemConfiguration folder (you will lose all of your network settings data!)
    3. Shutdown the machine completely
    4. When off, hold Shift-Control-Option-Power for 8 seconds, then release
    5. If this worked correctly, then nothing should happen (you’ve just cleared the SMC)
    6. Start ‘er back up!

    • Same problem with my iMac 2010. solution Amir Ebrahimi solved the problem for me.
      I deleted the /Library/Preferences/SystemConfiguration folder and after restart everything is ok

      • Hey, I also experience slow wifi connection on the recently upgraded mountain lion (former os was Snow Leopard)

        Anyway, I wanted to apply the described fix just to find out that under /Library/Preferences/ I dont have any folder nor file called SystemConfiguration.

    • This kills Microsoft Outlook if you have it installed. You may want to make a backup of the folder first. Apparently, Microsoft keeps its Identity file in there. Other than that, it fixed my wifi dropping and slow internet issues.

      Turn off IPv6 or put in Google’s IPv6 DNS servers. Many websites, Google, Yahoo and Microsoft to name a few, now default to IPv6 first for name resolution. The problem is, no consumer ISP (that I know of) is handing out IPv6 addresses. So your machine tries to use IPv6 and fails. To turn off (ie disable) ipv6, open a terminal window (under Applications, then Utilities) and type the following command:
      networksetup -listallnetworkservices

      This will list all the services on your computer (Ethernet, Wi-Fi etc). Then type:
      sudo networksetup -setv6off Wi-Fi (if you want to turn ipV6 off on the Wi-Fi).

      Or you could just add the Google IPv6 DNS servers as entries under Network Preferences, Advanced, DNS.

      Google’s Public DNS servers can be found here.

    • Hi. Thanks. Deleted the system configurations folder but after resetting the SMC and starting up… the network settings haven’t disappeared. Have I done something wrong? Once I delete the system configurations folder, do I need to empty the trash?

      • Not sure what is going on there. You should notice that all of the wifi networks that were remembered are gone. Is the wifi any better?

        • Hi. Thanks for your reply. No all wifi setting were still there… Not sure if wifi is better yet. My problem was actually a general wifi slowdown after which I would need to change the channel and then it speeded up again. But this was happening very often. In the meantime, no slowdowns. Time will tell…

          • One other thing we did because we were seeing odd drop-outs of Wifi was to switch routers. We were using a SonicWall, which is incredibly difficult to configure. I picked up an Apple Airport Express and *poof* — wifi problems gone.

            • My router has the latest firmware but as it’s supplied by my internet provider, I can’t replace it! Oh well!

  • Apparently changing the MTU solves the problem in some cases.

    Open network perferences.
    Configure, set this to manual
    Type in 1453 in the box.

    I tried this a few hours ago and its been ok so far where as I had 4/5 drops this morning before changing it..

  • I purchased a mid-2012 MBP Retina and I’m experience wifi dropping and coming back on. Actually, it doesn’t actually show me as dropping the network, but I’m unable to get to any sites (e.g. Google), while all my co-workers can. I’m waiting to see if another co-workers newly bought MBP also has this problem. I think it may be faulty hardware.

    I also notice that my BT mouse drops out occasionally.

    Anyone else in this boat?

    • Same problem here. Everytime I’m on the bedroom and my bf connects on his computer, my MBPro mid-2012 stops any online activity, but pretends to be connected at full signal. If I go to somewhere nearer the router (it’s on the living room), I get to connect again. I’ve just deleted the system configurations folder and reseted the smc, but, since my bf’s not home, I can’t still tell if it worked.

  • This does not seem to be a Mountain Lion issue per se… But maybe an update to the firmware on the Airport when ML was installed. I have an AP Extreme mid 2011 model that is causing a slowdown.

    I have two other access points, one an older D-Link 802.11n that I just re activated and there is no problem with network speeds when using this connection.. As fast as the AP used to be before the problem. The other access point is the unit that comes with Uverse, an 802.11g unit–again no issue. Switching between the units that are all active at the same time shows that the Airport is not working correctly. No changes were made to the Airport settings, save the ML install.

    Waiting for Apple fix…

  • Exact same issue with a June 2012 MB Pro since upgrading to Mountain Lion, Wifi speed was fine before.

    Tried to connect to Airport device via ethernet and speed is back to normal.

  • I have a 2008 Mac Pro that seems to lose ethernet connection once the computer goes to sleep. Only way to get it back is to restart the computer. Also had wifi problems on my 2011 macbook pro and first edition macbook air. (You would think I would have learned my lesson after updating the macbook air, but my motto when it comes to computers is “if its not broken, you’re not trying hard enough). Looking forward to a solution, Actually had more issues with Lion as far as software compatibility, so can live with the inconvenience for now. Apple is always forthcoming about problems with its products, so I am sure these issues will be fixed in no time. In Apple lingo this won’t be a fix, it will be a new feature added to the Mountain Lion OS.

  • I forget where I saw this suggested. Turning off Bluetooth has resolved the issue for about a day so far for me. Curious if it will last.

    None of the other solutions on the web worked even temporarily – creating new location in Network, etc.

  • Same issue as everyone – late 2010 MacBook Pro – working fine and upgraded to Mountain Lion – now, as soon as computer sleeps, no WiFi – have to restart or even shut down completely to reconnect (happens on whatever network I happen to be on) – huge pain since I travel and am constantly closing lid of computer which causes the problem almost everytime. APPLE – PLEASE FIX ASAP!!

  • I had a network here that my mac did not find anymore. I solved that issue by deleting all networks my mac remembered. After that I did see the network and was able to connect again.

  • Same problems with 17″ MacBook Pro. as others described. WiFi not working as it did before install. Went to Apple Store, guy sez everything OK. Got home, still not working. Router OK for PC.

  • Got the same issue here, MBP 13″, 2010: everything ran fine under Lion. Even though WiFi connection strength indicates full signal the connection becomes terribly slow. In “Activitiy Viewer” under Network I get something like 200 Bytes per second (Bytes!).

    There is no other device syncing, I just had this issue 10 minutes ago and the MBP was the only device active in the network (no photo stream updates to/from other devices, for instance).

    I am typing this on an iMac with Snow Leopard which is just 1 meter away from the MBP – not having these issues (connected to the same exact router via WiFi). So can’t be some “signal hole” or whatever…

  • Same problem here, MacBook Pro 13″, 2010: Ran fine on Lion, now at times it gets *terrible* slow! Thunderbird looses connections to mailboxes. Firefox somethimes even times out when looking for etc.

    What’s going on here?

  • I´ve the same problem on my Mac Pro 2009 Dual 2.26 i´m using an USB Wifi adapter from Ralink using the shipset RT 2860 if I´m not wrong, Everything used to work GREAT on Lion, after Istallin ML, my wifi doest work at all, it does not sustain a wifi connection, keep dropping it every 5 sec. Im using the latest driver for my adaptor. Tried to call Apple Care service, but here in BRAZIL looks like NOBODY works there, since nobody picked up the damn phone. So please let me know how I can fix this issue.

    • Early 2008 Mac Pro here. Same connect/disconnect every 5 seconds or so with the Ralink chipset in a NewerTech adapter. Not positive about which chipset it is, though I think it’s the 2870. Any news/help would be appreciated! Can’t use ML till this gets fixed.

  • I have the same with problem with my MBA (2012). It’s an intermittent problem and when it occurs wi-fi access is painfully slow. No problem using my old laptop on the same wi-fi system.

  • I have the same problem: after upgrading from 10.7 to 10.8 my wifi became painfully slow; now i download at 40kbps on a 20mb adsl on wifi. No issues with ethernet cable. I have tried to reset pram, smc, remove wifi connection and create a new one without success.

  • I have an issue with my MacBook Pro Late 2011 since upgrading to Mountain Lion. My issue is upon waking up it has lost the internet connection, sometimes having to reboot before being able to reconnect. I did not have any problems prior to updating.

    • I have figured out that issue. If your wifi router is still using WEP and not WPA or WPA2, then you need to update that. Almost all routers are capable of doing it.

    • Hi

      Does anyone here’s having problem with wifi and mountain lion?

      1. I have a Late 2011 MacBook Pro 15″ bought in June 2012
      2. Upgraded Mountain Lion On Wed July 25th (I know now it wasn’t the wise thing to upgrade on the release date)
      3. Started having Wifi issue since July 30th
      4. Mac can’t connect to wifi after waking up or turning on
      5. My other mobile devices are connected and functioning properly (Android Phone, Android Tablets, Window Laptop and iPhone)
      6. The only thing I can get connected is to power off my router and turn it back on
      7. Here’s the weird thing, when my MacBook Pro can’t connect to wifi after waking up or turning on, if I turn off wifi on my other devices and turn them back on they too cannot reconnect. (I do this to rule out a defective router) I would need to power off/on my router for everything to reconnect. It seems like once the MacBook is having problem with connecting to a wifi connection it affects all the devices that are trying to connect to the same connection. If the other devices have already been connected prior the Mac/Wifi issue, they are connected.

    • I’m having the exact same problem as you are. I also checked WEP/WPA/WPA2 settings are the router is set to WPA/WPA2….so that isn’t the problem.

  • I’ve got this issue. Wifi internet was great, then upgraded macbook air to mountain lion 2 days ago. Now macbook air is getting downloads of 0.9 Mbps at home and work. For some reason it works great at the apple store, and I cant explain that. Also, every other device on wifi at home, including pc laptop, 2 ipads, and my android phone are downloading at 6 to 13 Mbps over wifi. Mountain lion upgrade is the only change since my macbook air slowed down. Apple tech support and genius bar are attempting various fixes, but so far keep saying that the computer looks fine, no explanation for wifi problems. We’ll see what happens.

  • Haven’t noticed any WiFi issues but my Bluetooth is completely gone. Tried all the fixes – PRAM, SMC, deleted prefs, etc.
    Genius Bar tomorrow.

  • Having major wifi issues with Mountain Lion….really annoying and wish I hadn’t upgraded. If this keeps up, I may be forced to restore back to original.

  • Similar issue on my 2008 iMac. According to, my upload and download speeds are normal, but my ping is 45-72 ms. Prior to the upgrade my ping was under 20 ms. My 2011 Air is behaving normally. My connection is wifi. Unfortunately, I don’t have a long enough ethernet cable to test a direct connection.

    • aaaaand, of course, as soon as I post the issue seems to have self-corrected. Speeds are normal again.

      • well, in fact it doesn’t change anything. I just notice that when i turn off wifi, it works well for a few seconds when i turn it on again, and then it goes in slow mode

        • Philip,

          I also applied fix #1 as described in the link, and it worked the first time, and lasted for about a week.
          Then, wifi stopped working again, and this time this fix didn’t work.

          What DID work eventually was to upgrade the firmware of my router (mine is TP-Link).
          Someone online said that the improvements of mountain lion regarding communication was too much to handle for old firmware…(: go figure.
          Anyways it worked for me, give it a try.