Although most of the bugs in a particular OS get ironed out before the final version is released, some bugs still persist or come out in the open after the release. The OS X Mountain Lion upgrade has been error free for most of the users, but there are quite a few users who are experiencing unusual wireless connectivity issues.

WiFi problems affecting OS X Mountain Lion users.

Users who were experiencing the problem, complained that their WiFi connections drop at random and that their Macs just don’t stay connected to the wireless network for long, sometimes the Macs reconnect and sometimes they don’t. Many people have come up with different solutions that seem to solve the problem and here are the two that seem to fix the issue in most of the cases. So if you are one of those experiencing the problem, don’t panic, you are not alone, and this issue is definitely solvable. For best results try combining both the tips –

Fix #1: Add a New Network Location and Renew DHCP

This method is especially meant for those people who have upgraded from a previous version of OS X Mountain Lion. Even if you don’t come under this category and have WiFi drop issues, use this method as it is the most consistent and successful method of combating wireless issues.

  • Go to the menu marked by the Apple logo and click on System Preferences.
  • In the System Preferences choose Network.
  • Pull down the location menu and choose Edit Locations….
  • Click on the [+] button, add a new location and give it whatever name you want to. Then click on Done.
  • It will take you back to the Network Screen where you have to click on the Network Name menu and join the wireless network.

The wireless connection should now be active and working fine. Renew the DHCP lease as an added precaution so that the connection keeps working properly without any hindrance. To renew the DHCP lease follow these steps:

  • In System Preferences, from the Network Panel, click on the Advanced button in the lower right corner, and then click on the TCP/IP tab.
  • Configure IPv4 should be set to to Using DHCP. Then click on Renew DHCP lease and then click on Apply when you are prompted to do so.
  • The appropriate DHCP settings will be renewed from the connected router. Then click on OK and come out of System Preferences.

The renew DHCP lease

This method had earlier solved a similar problem affecting OS X Lion users and has so far been effective in solving the problem on OS X Mountain Lion as well.

Fix #2: Change MTU Size to prevent Dropped Connections

This method might be a bit difficult and might seem a bit too geeky for you, but follow the steps and you will be fine. MTU stands for Maximum Transmission Units and controls the size of the largest packet size allowed for transmission over the network. If this setting is greater than network capacity then the computer will experience what is called as packet loss, which results in dropped connections. The default setting of 1500 is quite high and some networks reject packets of that size so the user must set it to 1453 which is small enough to be accepted by most networks to maintain a consistent connection and is large enough to not cause any slowdown. Some folks call it a magic number, and it is actually an old Cisco networking secret.

  • Open System Preferences from the menu marked by Apple logo. Then select Network.
  • Click on the Advanced button in the lower corner and then select the Hardware tab.
  • Pull down the Configure menu and set it to Manually.
  • In the MTU pull down menu select Custom and set the field to 1453.
  • Click on OK and come out of Network Preferences.

You will be joined to the wireless network. Close System Preferences and notice the change.

Other Methods and Tips

Rebooting the Mac has also been found successful to resolve the problem in some cases.

You also might be experiencing network problems due to interference with other neighboring networks. So you should check the channel of the router you are connected to and make sure that the connection strength is strong.

You can even use the new WiFi Scanner built into Mountain Lion to check the network health.

Users have also been successful in solving the problem by performing a clean installation of Mountain Lion, especially the ones who are upgrading from OS X versions that came before OS X Lion, but ideally this method should be your last resort because you can simply solve the problem by following the instructions listed above.

via OS X Daily 

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