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Pretty regularly, customers will bring in a Mac that is intermittently dropping its Wi-Fi signal. This is a very frustrating issue, and it can also be a difficult one to diagnose. Every basic home network setup is different in that the hardware is different, the environment is different, the amount of load/strain varies, and the ISP can be different. All these factors must be considered to produce a solution.

Nine times out of ten, this issue is not replicable on our service department Wi-Fi network, and therefore cannot be definitively diagnosed. Sometimes, changing basic network settings within System Preferences will resolve the issue, but that’s not always enough. Often, the best troubleshooting of wireless issues involves doing the work while the machine is in its home environment. That means either doing it yourself and doing the research, or hiring someone to attempt to resolve the issue for you, be it via an on-site visit or phone support.

So what do you do when you have done pretty much everything? One possible resolution for a slightly more advanced user is to adjust the size of something called the MTU, or Maximum Transmission Units. The MTU determines the maximum amount of data each packet can carry through the network. 1500 is typically the default for most Macs, and also the largest allowed by most basic networks. This means up to 1500 bytes can be carried in each packet over the network.

Generally, the larger the MTU size, the better your network efficiency, and I think Apple would agree with that, considering their default size is the maximum usually allowed. However, in some cases, the MTU size set on the computer can conflict with the some aspect of the network, causing it to intermittently lose its signal. This can be resolved by altering the MTU size slightly, within Terminal.

As always, use your best judgement when playing around in Terminal. Things can quickly go from good to bad if you you don’t know what you are doing. Now, with the usual disclaimer out of the way, follow these directions.

Open a Terminal window and type:

  • networksetup -getMTU en0
  • hit Return

Note: You may need to type en1 instead; it depends on which connection you are using. You can find out using Network Utility. This will tell you your current MTU size.

To change the size, type:

  • networksetup -setMTU en0 XXXX(new size)
  • hit Return

You can input whatever size you want; I would recommend keeping it relatively close to the original MTU size, for example: 50 fewer units (1500->1450). This setting is easy enough to change and test as part of your troubleshooting. Nothing is permanent, as you can easily change the MTU size back to what it was originally (using the aforementioned command) if this does not resolve your issue.

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