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How macOS Handles DNS
macOS uses a built-in DNS resolver called mDNSResponder that manages all DNS lookups on the system. When you connect to a network, macOS automatically receives DNS server addresses from the router via DHCP. These are usually your ISP's DNS servers, which means every domain you look up is logged by your ISP unless you've manually changed your DNS settings.
macOS also supports network service ordering, which determines which network interface takes priority. If your VPN connection isn't set as the highest priority service, DNS queries may be routed through your regular WiFi or Ethernet connection instead — causing a DNS leak.
Why Macs Are at Risk on Public WiFi
Public WiFi networks are particularly dangerous for Mac users. When you connect to a coffee shop, hotel, or airport WiFi, the network's DHCP server pushes its own DNS settings to your Mac. These DNS servers are controlled by whoever runs the network — and they can see every site you visit. Worse, an attacker on the same network could set up a rogue DHCP server that redirects your DNS to a malicious resolver, enabling phishing attacks and traffic interception.
Even if you're using a VPN on public WiFi, your Mac may still send some DNS queries outside the VPN tunnel during the connection handshake or if the VPN momentarily drops. For more on this topic, see our guide on DNS leaks on public WiFi.
How to Test and Fix DNS Leaks on Mac
- Run our free DNS leak test while connected to your VPN. If your ISP's DNS servers appear in the results, you have a leak.
- Open System Settings → Network, select your active connection, and click Details → DNS.
- Remove any ISP-assigned DNS servers and add a secure provider: 1.1.1.1 (Cloudflare) or 9.9.9.9 (Quad9).
- Click OK, then Apply.
- Flush your DNS cache in Terminal:
sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder - Re-run the DNS leak test to confirm the fix.
For a complete walkthrough covering all platforms, see our step-by-step DNS leak fix guide.
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