If it isn’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 severe hit when it came to networking. When it launched Yosemite, Apple ditched a process called ‘mDNSResponder,’ a crucial part of Bonjour, the autodiscovery 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.
What is mDNSResponder, and why is it on my Mac?
As many users discovered a few years ago 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 quickly. 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 that 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 correctly.
Specifically, mDNSResponder is a daemon 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 the ‘discoveryd’ process, and things went badly wrong — perhaps no surprise given that mDNSResponder had been fine-tuned for over a decade and that networking has always been one of the most troublesome parts of macOS.
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 making any services that rely on autodiscovery, like Hand-off and Continuity, unusable.
How to flush your DNS cache
If you face any issues or see alerts about the mDNSResponder, flush your DNS cache with a utility like CleanMyMac X. It helps resolve some server connection problems.
After you install the app, click Maintenance and select Flush DNS Cache. Now, click Run.
If you’ve noticed that your Mac has become sluggish, it can be difficult to work out the problem. You could use Activity Monitor to identify mDNSResponder, but all those processes are challenging to understand. CleanMyMac X can help.
Check the background items taxing the CPU
To get a better grip on background processes on your Mac, try this free analyzer tool in CleanMyMac X. This little Menu app analyzes memory and other behind-the-scenes parameters of your machine. Once you download the main CleanMyMac X app, click on the small iMac icon in the top menu bar.
On the CPU tab, you can see what is straining your processor. Look through the list of apps it’s showing. There may be a few surprises. Also, see the Memory tab to get a real-time view of memory usage. Quit apps that are too demanding.
CleanMyMac X also has an Optimization tool that 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.
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.
