iMac switching networks

It is important that if you have multiple Macs and iCloud Keychain sharing that you clean out the "Preferred Networks" of any references to that Netgear with "None" for Security.

System Preferences -> Network -> WiFi interface on the left -> Advanced -> Wi-Fi -> Preferred Networks:

Select each network to remove, and click on the [-] button.

ALSO, you can re-order the list with your preferred networks at the top of the list, my just dragging any network name up or down in the list.

When your Mac attempts to connect to WiFi, it goes through this list from top to bottom looking for a network it can attach to. First, one that works will be selected.

So make sure your preferred network(s) are at the top of the list.

Also if you have your preferred networks at the top of the list, your Mac will connect to WiFi faster as it will not need to try unavailable networks first, or worse find the unsecured Netgear network before it finds your preferred network.

I think between re-ordering the list to put your preferred network at the top of the list and removing the Netgear network from ALL the Macs where you are sharing your Keychain via iCloud should solve your problem.

System Preferences -> Network

That will not stop your Mac from seeing other networks, but it should not automatically join any network that is NOT already in your

System Preferences -> Network -> WiFi interface -> Advanced -> Preferred Networks list.

That is why it is important to remove any networks you do not want to automatically join from your Preferred Networks list.

NOTE: If you have multiple Macs, which are using iCloud and you are sharing your Keychain, then you may need to make sure you remove the unwanted network from every one of them, as your preferred networks are shared via your Keychain.

Make sure you have a complete and current external backup or two here.

Okay; one other option is if iCloud Keychain is in use; that can get tangled here. Known networks can be populated from there, so I'd next try disabling iCloud Keychain, purging the list, and re-adding.

https://discussions.apple.com/thread/7755049

There's a complete brute-force approach and some potential work-arounds here:

https://discussions.apple.com/thread/6077377

The above might expunge the list from the known networks, though there've been various discussions of those entries re-populating themselves from iCloud.

Another potential—and really gnarly—approach to change this behavior uses the airport command at the command line and selecting a different JoinMode and JoinModeFallback setting.

Caveat: I've not tried this in detail, and don't presently have a selection of Wi-Fi networks to choose from...

The airport command is hidden away here:

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resource s/airport

The JoinMode options are Automatic, Preferred, Ranked, Recent and Strongest

The JoinModeFallback options are Prompt, JoinOpen, KeepLooking and DoNothing

To see the details of the current preferences settings:

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resource s/airport prefs

To set...

sudo /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resourc es/airport prefs JoinMode=Automatic

I've tweaked a few settings, and it seems to work as expected. Here are my current defaults:

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resource s/airport prefs

AirPort preferences for en1:

DisconnectOnLogout=NO

JoinMode=Preferred

JoinModeFallback=DoNothing

RememberRecentNetworks=YES

RequireAdminIBSS=NO

RequireAdminNetworkChange=NO

RequireAdminPowerToggle=NO

WoWEnabled=YES

Also see

http://hints.macworld.com/article.php?story=20110223124409352

https://discussions.apple.com/thread/6791217

 > System Preferences > Network > select your Wi-Fi network controller.

Select Automatically Join only for the networks you're interested in (and de-select it for others), and maybe also select Ask to Join New Networks.

Now click Advanced button, and select Wi-Fi tab > now remove all but the networks you want to use.

Would requiring administrator access prevent changing networks? Yes.

It won't change any lurking problems with the signal and with the interference.

Moving from 2.4 GHz to 5 GHz Wi-Fi can be one of the few choices for avoiding the wreckage that is 2.4 GHz in populated areas.

Yes. That'll ask you for for permission to switch, if it runs into trouble. That prompting might get tedious, but it'll also avoid switching networks when you don't want it to happen.

Multiple uncoordinated Wi-Fi networks interfere, unfortunately. There are only three non-overlapping channels on 2.4 GHz Wi-Fi. Wi-Fi routers set to look for a channels automatically can also end up looping through the search as each Wi-Fi router hits trouble and tries another channel, and the whole process loops through all the routers set for automatic channel selection.

Here's what I'd do...

Launch Terminal.app from Applications > Utilities

Enter the following two commands—each command is a single, long line—to show the current settings, and then select only Preferred networks. The first command will view your current settings for these preferences, and will allow you to select the original settings if you want to revert.

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resource s/airport prefs

sudo /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resourc es/airport prefs JoinMode=Preferred

The sudo command will require an administrative password.

I'd guess that the first command will show Automatic for your current JoinMode setting, or that there might be no JoinMode setting. (I saw that latter case on a local High Sierra system.)

Now select the fallback processing from one of the following two commands: either don't do anything, or prompt the user. I'd start with DoNothing, though Prompt will probably also do what you want.

sudo /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resourc es/airport prefs JoinMode=DoNothing

or

sudo /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resourc es/airport prefs JoinMode=Prompt

Then I'd see if things are working the way you'd prefer, around your preferred networks. This also assumes your preferred networks are just the ones you want, and don't have the NetGear network in the list.

Alternatively, you can try to figure out which local person has that network configured, and suggest that they close it. Post some signs around, if you can't wander the area and figure out where that Wi-Fi network is strongest.

I will also add, you could track down the neighbor with the Netgear router and ask them to put a password on their WiFi network. Just a thought.