Mac DNS Lookup Failed — Cannot Resolve Hostname Troubleshooting

Overview

Fix Mac DNS lookup failures causing 'server not found', 'DNS lookup failed', and inability to load websites while other network services work.

Key Details

• macOS uses mDNSResponder for DNS resolution, which can crash or become corrupted
• DNS issues on Mac can coexist with working IP-level connectivity (ping by IP works but names fail)
• VPN software frequently modifies DNS settings and may not restore them properly
• macOS stores DNS settings per-network interface, and wrong settings can persist across networks
• /etc/resolv.conf on Mac is auto-generated — manual edits are overwritten

Common Causes

• mDNSResponder service crashed or hung
• DNS servers configured in network settings are unreachable
• VPN modified DNS settings and did not restore them after disconnecting
• Wi-Fi network providing broken DNS server via DHCP
• macOS DNS cache corrupted with stale or incorrect entries

Steps

1. 1Flush DNS cache: sudo dscacheutil -flushcache && sudo killall -HUP mDNSResponder
2. 2Check DNS settings: System Settings > Wi-Fi > Details > DNS — ensure valid servers listed
3. 3Set manual DNS: add 8.8.8.8 and 1.1.1.1 in DNS settings for your network
4. 4Test resolution: nslookup google.com in Terminal — if it fails, DNS is the issue
5. 5Restart mDNSResponder: sudo killall mDNSResponder

Tags

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Frequently Asked Questions