If you’re experiencing connectivity issues, you may need to remove and reconnect to the network from the list of older, known networks.

Steps for this process are listed at the bottom of this Apple support page - Remove a Wi-Fi network from your known networks.

After following the steps, restart your computer before trying to connect again.

If you're troubleshooting a Mac connection that feels "stuck," clearing the DNS cache is essentially giving your computer a fresh map of the internet. 

Listed first are the most common reasons for flushing DNS on a Mac, followed by a link to the instructions.

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Removes "Stale" Information
Think of the DNS cache as a local address book where your Mac stores the IP addresses of websites you’ve visited. If a website moves to a new server or changes its settings, your Mac might still be trying to use the old, outdated address.

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Resolves "DNS Spoofing" or Corruption
Sometimes, the cache data becomes corrupted due to technical glitches or malicious software.

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Bypass Configuration Hang-ups
When you switch networks (like moving from a coffee shop to your home), your Mac sometimes clings to the DNS settings of the previous network.

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See Flush DNS Cache on Mac for instructions on clearing the DNS cache for your version of macOS.

ISPs (Internet Service Providers) often have "clunky" DNS servers that can be slow to respond. Every time you click a link, your computer has to wait for that DNS lookup. Using Google's DNS can help.

Google has one of the largest "address books" in the world. Because so many people use their service, the website you’re trying to visit is almost certainly already in their cache, leading to near-instant results.

IMPORTANT: Before you change your DNS settings to use Google Public DNS, ensure you have written down your current server address or settings if present. It is very important that you keep these numbers for backup purposes, in case you need to revert to them at any time.

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Change to Google DNS Settings
Example below is for changing DNS server settings on macOS 10.15:

1. Click on the Apple menu > System Preferences > Network. 
2. If the lock icon in the lower left-hand corner of the window is locked, click the icon to make changes, and when prompted to authenticate, enter the computer password.
3. Select the connection for which you want to configure Google Public DNS.
4. To change the settings for a Wi-Fi connection, select WiFi, and click Advanced. 
5. Select the DNS tab.
6. Click + to replace any listed addresses with, or add, Google IP addresses at the top of the list:
   
   • For IPv4: 8.8.8.8 and/or 8.8.4.4.
   • For IPv6: 2001:4860:4860::8888 and/or 2001:4860:4860::8844.
7. Click OK > Apply.

This process forces macOS to create all new preference files for wireless networking, which can be an effective troubleshooting strategy. 

This process is especially useful if the problems began after upgrading versions of macOS or even installing incremental system updates.

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Instructions

1. Pull down the WiFi menu from the top right and turn wireless off.
2. From any Finder window, press Command+Shift+G to bring up Go To Folder and enter the following path: /Library/Preferences/SystemConfiguration/
3. Locate the following files, copy them to the desktop in a folder for a backup, then delete them from the /SystemConfiguration/ folder:   
   
   Note: Do not delete plist files without backing them up first.
   
   
   • com.apple.airport.preferences.plist
   • com.apple.network.identification.plist
   • NetworkInterfaces.plist
   • preferences.plist
     
     
4. Empty the Trash and restart the Mac.
5. Turn wireless back ON from the menu and join your preferred network as usual.