WHAT IS MDNS:
mdnsd (Multicast Domain Name System Daemon) is Android's implementation of mDNSResponder, a part of upcoming Zero Configuration Networking. It allows you to automatically discover services and appliances attached to your network:
This daemon is continuously sending multicast messages (queries) to all hosts on local network at IP address
22.214.171.124 and UDP port
5353, also listening on the same port.
WHICH APPS USE MDNS:
Any app that makes use of Android's Network Service Discovery, will request
mdnsd running in background (1, 2, 3):
Adding NSD to your app allows your users to identify other devices on the local network that support the services your app requests. This is useful for a variety of peer-to-peer applications such as file sharing or multi-player gaming.
A quick search on forums will show many apps being blamed for excessive battery drainage becuase of using
mdnsd, e.g. Facebook and Firefox. The later has been gone through a bug in the past that caused the unexpected behavior. Now they have their own implementation of MDNS (4). Google Play Services also have built-in MDNS service (to discover Google Cast devices???) (5).
Devices that support NSD include printers, webcams, HTTPS servers, and other mobile devices.
AOSP's built-in apps Print Service Recommendation Service (com.android.printservice.recommendation) and Default Print Service (com.android.bips) also make use of NSD. So if you are using printing features on your device, those would be causing
mdnsd run in background. But the most common reason is ADBD (Android Debug Bridging Daemon) which force starts
HOW TO STOP MDNSD?
mdnsd is an init service (7) which can be stopped by triggers. Add a few lines to
# stop mdnsd on startup
# stop mdnsd when adbd starts/stops
You can also manually stop the service anytime by executing:
~# setprop ctl.stop mdnsd
Or you can directly kill the
mdnsd program as suggested by @DBX12. The service shouldn't restart because it's
oneshot. But if it's triggered again and again by some app or the OS, you can make the binary inexecutable (or delete) at all:
~# chmod a-x /system/bin/mdnsd
However this may break some apps' functionality.
All of the above solutions require root. If your device isn't rooted, the only way is to identify and stop using the app/feature that uses Android's NSD API or directly starts