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I would like to access my device as myandroidthing.local, as I can do it with my (both Linux and Windows) laptops. Is it somehow possible?

Most ideally, it could be done by some app what I can install from an app store.

Responses to the answer:

  • Android.local works. But it finds only one of my Android devices. Is there a way to replace the Android mdsnd with a better configurable one which allows changing the name it advertises?
  • Does running a patched mdnsd require a rooted device?
Glorfindel
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peterh
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1 Answers1

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My answer to Why is "mdnsd" draining my battery and how to stop it? explains the role of Android's mDNS Daemon which is an init service, started on demand. It provides Multicast DNS (host/domain name resolution) and DNS-SD (DNS-Based Service Discovery); both part of Zero Configuration Networking.

How to resolve Android's mDNS hostname to IP address?

Technically it's possible for DNS-SD to use the old unicast DNS to resolve the domain name found in the SRV record (of a broadcasted service) to an IP address. But mostly mDNS and DNS-SD are bound to each other. And this is the case with Android.

Android doesn't expose any setting or API to do only the name resolution (as mDNS Responder or Querier) and not the service discovery. Neither the name resolution mechanism uses mDNS. Android's mdnsd serves as mDNS broadcaster / responder only to DNS-SD service. You cannot use either of the both independently (as to my knowledge).

But there are a few options:

  • Run an app on your Android device with a discoverable service (even a dummy), which uses Android's official API (which in turn interacts with mdnsd underneath) to broadcast and discover services. So any other host on the local network with mDNS/DNS-SD capability can discover the service. For instance use avahi-browse command on a Linux system. Resolving the service provides the IP address of the Android device.

  • When mdnsd is running, Android device is already broadcasting itself with a hard-coded name: Android.local. If you don't want to broadcast a service, there's another option.

    ADB relies on mDNS to discover devices on local network by registering a service of type _adb._tcp (see references here, here and here). So enable "USB Debugging" in Developer Options and you'll see mdnsd running on your device.

    Or on a rooted device start mdnsd alone, without starting ADB, by executing setprop ctl.start mdnsd or simply start mdnsd.

In both above cases, when mdnsd is running, executing avahi-resolve-host-name Android.local on a Linux PC should return IP address of your Android device.

What if two Android devices have the same hostname?

In case of name conflict, as the name Android.local is hard-coded, the Android device which joins later automatically renames itself to Android-2.lcoal, Android-3.local and so on (see reference here). So you can resolve the names accordingly.

Any option to change the mDNS hostname?

Coming to the next problem, what if your OEM/ROM developer removed or modified the mdnsd service, or if you want to run with a name of your choice, not the hard-coded one?

  • Build and run your own more configurable mDNS responder like Avahi on Android device.

  • Even simpler, patch and rebuild Android's mdnsd to receive a commandline argument for name, or read from a config file if exists.

    No, it doesn't need a rooted device. The patched mdnsd binary should run fine from adb shell, or even on a terminal emulator app like Termux. As of this writing, there's only one syscall in mdnsd source code which the seccomp blocks for apps. But it can be removed easily. Neither the DAC or MAC block the execution.

Irfan Latif
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    Hehh, very funny! Android.local works. Problem is, it finds only one of my androids... somehow I need to change the name it advertises. – peterh Oct 07 '21 at 16:37
  • Thanks! Unfortunately, the source clearly shows that there is no way to change it. Next question, is there a way to replace the android mdsnd with a better configurable one. – peterh Oct 07 '21 at 16:47
  • The simplest way is to patch and rebuild Android's mdnsd to receive a commandline argument for name, or read from a config file if exists. – Irfan Latif Oct 07 '21 at 21:34
  • That requires root and rooting a phone means that I risk bricking it. Furthermore, there is really free (as in freedom) android image only for a few phones. Sad, but I still can not have a rooted phone on this reason. Furthermore, I can not root the phones what are not mine, but I can talk to their owner to install X app. – peterh Oct 07 '21 at 23:34
  • Ok, so the mdns name is hardcoded to android.local. What is with the services? I think, I can install any app creating a service, and then use the service name to localize the ip. – peterh Oct 07 '21 at 23:36
  • @IrfanLatif How exactly would you go about compiling it? Since it's forked from Apple's code, there's still a lot of references to it. – StarDust Dec 13 '21 at 16:27
  • @StarDust IIRC it didn't take me more than a few minutes the last time I did it. Clone Google's repo, not Apple's. The former have already made the required changes for Android. Just make your small changes, if you want to. And compile it with NDK. – Irfan Latif Dec 13 '21 at 18:13
  • Ok, I finally got it. And it works perfectly! I'll post an answer soon. – StarDust Dec 14 '21 at 04:37
  • And here it is. Hopefully, someone benefits from this and doesn't go through everything I needed to do: https://stackoverflow.com/a/70343905/15436715 – StarDust Dec 14 '21 at 11:51
  • For reference: Starting from November 2021, Android resolver supports mDNS .local resolution. – Irfan Latif Jun 05 '23 at 19:48