What is mDNSResponder and why is it on my Mac?

If it ain’t broke, don’t fix it is a rule that Apple may wish it had heeded when it released Yosemite back in 2014. Why? Because Apple’s famed ‘it just works’ ease of use took a serious hit, at least when it came to networking. When it launched Yosemite, Apple ditched a process called ‘mDNSResponder’, which was a key part of Bonjour, the auto-discovery system for devices on a network. Without mDNSResponder, Bonjour ran into a heap of trouble on lots of Macs. And it wasn’t long before users started complaining of bugs in the system. 

mDNSResponder on Mac

What is mDNSResponder and why is it on my Mac?

As many users discovered when they installed Yosemite, mDNSResponder is a critical part of the Bonjour networking protocol. Bonjour is the thing that allows your Mac to ‘see’ other devices like computers, printers, and storage devices on your local network and connect to them easily. If you’ve ever noticed a printer or computer in the sidebar in the Finder that just appeared there, that’s Bonjour — it ‘discovered’ it on your local network and allowed you to see it so you can connect if you want. Noticed an app pop-up on the Dock on your Mac when you use it on an iPhone or iPad close by? That’s Bonjour too. And mDNSResponder is key to Bonjour working properly.

Specifically, mDNSResponder is a daemon that’s responsible for discovering services running on other devices on the local network. It also handles DNS requests for services that need to connect to the internet. Apple replaced it with a service called ‘discoveryd’ process in Yosemite and things went badly wrong — perhaps no surprise given than mDNSResponder had been fine-tuned for over a decade and that networking has always been one of the most troublesome parts of macOS.

Did you know? 

Ars Technica reported that when Apple put mDNSResponder back into macOS, it was able to close 300 separate bug reports. That shows you just how much an effect removing it had on macOS and demonstrates that even Apple gets it wrong sometimes.


What’s the problem with mDNSResponder?

Some Mac users have reported that mDNSResponder’s network usage is causing problems on their Mac, and that it’s flooding the network with ‘junk packets’ — traffic that occupies bandwidth but serves no purpose. They discover this using tools that monitor network traffic. For that reason, they want to remove or disable it. 

However, removing mDNSResponder will break Bonjour and make discovering and connecting to other devices on the network impossible. You could disable Bonjour altogether, but that would mean manually entering details for every device you want to connect to and make any services that rely on auto-discovery, like Hand-off and Continuity, unusable.

Tip: If you face any issues or see alerts about the mDNSResponder, flush your DNS cache with a free tool in CleanMyMac X. It helps resolve some server connection problems. 

Get a free version of the app here

After you install the app, click Maintenance and tick Flush DNS Cache.

If you’ve noticed that your Mac has become sluggish, it can be difficult to work out what the problem is. You could use Activity Monitor to identify mDNSResponder, but all those processes are difficult to understand. CleanMyMac X can help.

CleanMyMac X has a menu item that you can keep active even when you quit the main app. It allows you to monitor CPU usage, network activity, and free up memory. You can get more information on resource hogs within the menu item, and also quit apps that are too demanding.

CleanMyMac X Health Monitor


The main CleanMyMac X application has an optimization tool that also highlights heavy consumers of resources, allowing you to take control of them. And it can identify and shut down applications that have stopped responding due to a problem. 

Optimization tools in CleanMyMac X



As you can see mDNSResponder isn’t a virus, as some people think when they see it running in the background. It’s an essential component of macOS that allows the automatic discovery of devices on the local network in Bonjour. So you should definitely not try and remove it. If you think it’s making your Mac slow, there’s probably another explanation. And to find out what it is, you can use CleanMyMac X’s arsenal of tools. Once you’ve identified the problem, CleanMyMac can help you solve it by freeing up RAM or quitting hung processes.

CleanMyMac X
CleanMyMac X

Your Mac. As good as new.