mDNSResponder is the macOS DNS daemon: it resolves the web addresses your Mac looks up and runs Bonjour, which finds printers, AirPlay devices and shared drives nearby; it's part of macOS and listens on UDP port 5353 by design. If browsing is slow or it uses a lot of CPU, flush the DNS cache and check which DNS servers your Mac uses with 'scutil --dns'.
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One Mac, macOS 26.5 (25F71) on Apple silicon, read with ps and codesign on October 29, 2026
| Path | /usr/sbin/mDNSResponder |
|---|---|
| Runs as | _mdnsresponder, a macOS system account |
| Signed by | Apple (Software Signing), identifier com.apple.mDNSResponder |
mDNSResponder is the macOS daemon that implements Bonjour, Apple's zero-configuration networking protocol. It handles multicast DNS (mDNS) for local network service discovery — allowing your Mac to find AirPrint printers, AirPlay devices, shared drives, and other services on your local network without manual configuration. It also manages DNS resolution and caching for all network connections.
High CPU usage on networks with many Bonjour-enabled devices broadcasting services
DNS resolution delays causing slow web browsing and app connectivity
Memory growth over time from accumulated DNS cache entries on long-running systems
Network discovery failures where AirPrint printers or AirPlay devices are not found
Run 'sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder' in Terminal. This clears all cached DNS records and forces mDNSResponder to perform fresh lookups. It resolves most DNS-related browsing issues and stale service discovery.
Run 'scutil --dns' in Terminal to see your current DNS configuration. Verify that the DNS servers listed are correct and reachable. Misconfigured or unreachable DNS servers force mDNSResponder to time out repeatedly, causing high CPU and slow browsing.
Run 'sudo killall mDNSResponder' in Terminal. launchd will restart it immediately. This performs a full restart of the DNS and Bonjour services, re-discovering all local network services and rebuilding the DNS cache from scratch.
Go to System Settings > Network > Wi-Fi > Details > DNS and remove any manually configured DNS servers that may be causing issues. Alternatively, set reliable DNS servers like 1.1.1.1 (Cloudflare) or 8.8.8.8 (Google) to bypass ISP DNS issues that mDNSResponder may be struggling with.
mDNSResponder running with low CPU usage is completely normal — it handles all DNS lookups on your Mac. Be concerned if it sustains more than 20% CPU for extended periods, which may indicate a DNS resolution loop, an unreachable DNS server, or excessive Bonjour traffic on your local network. If web browsing is slow but your internet connection tests fine, mDNSResponder DNS issues are a likely cause.
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No. mDNSResponder is a core Apple system daemon that handles all DNS resolution and Bonjour network service discovery on macOS. It is essential for web browsing, finding AirPrint printers, AirPlay devices, and all other local network services. It is code-signed by Apple and protected by System Integrity Protection.
High CPU from mDNSResponder typically indicates DNS resolution issues. Common causes include unreachable DNS servers (causing timeout loops), a very large local network with many Bonjour devices, or a corrupted DNS cache. Flushing the DNS cache with 'sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder' resolves most cases.
Bonjour is Apple's implementation of zero-configuration networking (zeroconf). It allows devices on a local network to discover each other automatically without manual setup. When your Mac finds a nearby AirPrint printer, an Apple TV for AirPlay, or a shared Time Machine drive, that is Bonjour (mDNSResponder) at work. It is fundamental to the Apple ecosystem's seamless device integration.
Yes. Since mDNSResponder handles all DNS resolution, issues with it can make web browsing and app connections feel slow even when your underlying internet connection is fast. Symptoms include long delays before pages start loading. Flushing the DNS cache or changing to a faster DNS server (like 1.1.1.1 or 8.8.8.8) usually resolves this.
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