Mac DNS Lookup Failed — Cannot Resolve Hostname Troubleshooting

Fix Mac DNS lookup failures causing 'server not found', 'DNS lookup failed', and inability to load websites while other network services work. This guide covers everything you need to know about this topic, including common causes, step-by-step solutions, and answers to frequently asked questions.

Here are the key things to understand: 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. Understanding these fundamentals will help you diagnose and resolve this issue more effectively.

The most common reasons this occurs include: 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. Identifying the root cause is the first step toward finding the right solution.

To resolve this, follow these recommended steps: Flush DNS cache: sudo dscacheutil -flushcache && sudo killall -HUP mDNSResponder. Check DNS settings: System Settings > Wi-Fi > Details > DNS — ensure valid servers listed. Set manual DNS: add 8.8.8.8 and 1.1.1.1 in DNS settings for your network. Test resolution: nslookup google.com in Terminal — if it fails, DNS is the issue. Restart mDNSResponder: sudo killall mDNSResponder. If these steps do not resolve the issue, consider consulting additional resources or a qualified professional.

This article is part of our Mac Error Codes collection on Error Codes Wiki. We provide comprehensive, up-to-date information to help you find solutions quickly.