Flush DNS and change DNS servers

Unblock a site that no longer resolves and try other DNS.

1. Flush the DNS cache:

   sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

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2. List the network services:

   networksetup -listallnetworkservices

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3. Set DNS servers (e.g. Cloudflare and Quad9) on Wi-Fi:

   networksetup -setdnsservers Wi-Fi 1.1.1.1 9.9.9.9

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4. Go back to the DNS provided by your router:

   networksetup -setdnsservers Wi-Fi empty

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5. Test name resolution:

   dig example.com +short

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