No. mDNSResponder is a core part of macOS.
Every app's name lookups go through it, and it handles multicast DNS (Bonjour), which finds printers, AirPlay speakers and other Macs by .local names. It runs as the _mdnsresponder user from /usr/sbin/mDNSResponder.
mDNSResponder often tops the list of processes by connection count in network monitors, because it makes DNS queries on behalf of every app. That's also why “flush DNS” on a Mac means sending it a HUP signal: sudo killall -HUP mDNSResponder clears its cache. High CPU usually means some app is making a flood of lookups.
Facts
- Owner
- Apple (part of macOS)
- Network-related
- Yes
- Typical ports
- 53, 5353
- Block it?
- Don’t block it
What it connects to
| Host | Country | Purpose |
|---|---|---|
| Your DNS server (port 53) | — | Name lookups for every app |
| 224.0.0.251 / ff02::fb (port 5353) | LAN | Bonjour multicast DNS on your local network |
Should you worry?
No. mDNSResponder is a core part of macOS. Its network traffic is your apps' DNS lookups and Bonjour discovery. Blocking it breaks almost everything that uses the network.
Frequently asked questions
What is mDNSResponder?
Apple's DNS resolver and Bonjour service. It performs DNS lookups for all apps and discovers devices on your local network.
Why does mDNSResponder use so much network?
It does the DNS lookups for every app and Bonjour discovery for the local network, so its traffic adds up. Each lookup is small.
Can I disable mDNSResponder?
No. macOS needs it for name resolution; without it nothing could look up websites. Restart it with sudo killall -HUP mDNSResponder instead.