Configuring mDNS for Easy Access to Devices - Revision history

Mxl at 11:48, 20 February 2026

2026-02-20T11:48:30Z

← Older revision		Revision as of 11:48, 20 February 2026
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	Unlike the poor support for ''responding'' to queries, Android [https://source.android.com/docs/core/ota/modular-system/dns-resolver#mdns-local-resolution supports resolving mDNS addresses directly] as of November 2021. This should be transparent to applications, as it is built in to <code>getaddrinfo()</code>.		Unlike the poor support for ''responding'' to queries, Android [https://source.android.com/docs/core/ota/modular-system/dns-resolver#mdns-local-resolution supports resolving mDNS addresses directly] as of November 2021. This should be transparent to applications, as it is built in to <code>getaddrinfo()</code>.

			[[Category:System_Configuration]]

Mxl at 09:58, 20 February 2026

2026-02-20T09:58:15Z

← Older revision		Revision as of 09:58, 20 February 2026
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	[https://en.wikipedia.org/wiki/Zero-configuration_networking Zeroconf] consists of a number of related concepts with the common objective of making simple networked services "just work". Initially it was implemented by Apple as Bonjour, but on Linux the re-implementation [https://en.wikipedia.org/wiki/Avahi_(software) Avahi] is usually used to provide Zeroconf. Although initially intended for discovering networked devices like printers or speakers, it can also be useful for accessing other hosts or smart home devices on the local network without hard-coding their address or hosting a name server.		[https://en.wikipedia.org/wiki/Zero-configuration_networking Zeroconf] consists of a number of related concepts with the common objective of making simple networked services "just work". Initially it was implemented by Apple as Bonjour, but on Linux the re-implementation [https://en.wikipedia.org/wiki/Avahi_(software) Avahi] is usually used to provide Zeroconf. Although initially intended for discovering networked devices like printers or speakers, it can also be useful for accessing other hosts or smart home devices on the local network without hard-coding their address or hosting a name server.

	The relevant concept in Zeroconf that makes this work is multicast DNS (mDNS) which can resolve hostnames inside a local network by using multicast broadcasts. The mDNS client sends a multicast broadcast asking for <code><name>.local</code>, and the host with the given name (typically the device's hostname) answers it (also multicast, so all devices can update their caches). My goal was to make various devices on my home network accessible over their mDNS address. This works unreliably out of the box, I've collected the steps I took to get it working more reliably.		The relevant concept in Zeroconf that makes this work is multicast DNS (mDNS) which can resolve hostnames inside a local network by using multicast broadcasts. The mDNS client sends a multicast broadcast asking for <code><name>.local</code>, and the host with the given name (typically the device's hostname) answers it (also multicast, so all devices can update their caches). My goal was to make various devices on my home network accessible over their mDNS address. This works unreliably out of the box, I've collected the steps I took to get it working more reliably. The irony of having to configure Zeroconf is not lost on me.

	MDNS is easily conflated with DNS service discovery (DNS-SD), which allows discovering specific services (e.g. print service, web server, etc.) once a host is known. Both are relevant, however technically these are two separate concepts under Zeroconf.		MDNS is easily conflated with DNS service discovery (DNS-SD), which allows discovering specific services (e.g. print service, web server, etc.) once a host is known. Both are relevant, however technically these are two separate concepts under Zeroconf.

Mxl at 09:56, 20 February 2026

2026-02-20T09:56:22Z

← Older revision		Revision as of 09:56, 20 February 2026
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	[https://en.wikipedia.org/wiki/Zero-configuration_networking Zeroconf] consists of a number of related concepts with the common objective of making simple networked services "just work". Initially it was implemented by Apple as Bonjour, but on Linux the re-implementation [https://en.wikipedia.org/wiki/Avahi_(software) Avahi] is usually used to provide Zeroconf. Although initially intended for discovering networked devices like printers or speakers, it can also be useful for accessing other hosts or smart home devices on the local network without hard-coding their address or hosting a name server.		[https://en.wikipedia.org/wiki/Zero-configuration_networking Zeroconf] consists of a number of related concepts with the common objective of making simple networked services "just work". Initially it was implemented by Apple as Bonjour, but on Linux the re-implementation [https://en.wikipedia.org/wiki/Avahi_(software) Avahi] is usually used to provide Zeroconf. Although initially intended for discovering networked devices like printers or speakers, it can also be useful for accessing other hosts or smart home devices on the local network without hard-coding their address or hosting a name server.

	The relevant concept in Zeroconf that makes this work is multicast DNS (mDNS) which can resolve hostnames inside a local network by using multicast broadcasts. The mDNS client sends a multicast broadcast asking for <code><name>.local</code>, and the host with the given name (typically the device's hostname) answers it. My goal was to make various devices on my home network accessible over their mDNS address. This works unreliably out of the box, I've collected the steps I took to get it working more reliably.		The relevant concept in Zeroconf that makes this work is multicast DNS (mDNS) which can resolve hostnames inside a local network by using multicast broadcasts. The mDNS client sends a multicast broadcast asking for <code><name>.local</code>, and the host with the given name (typically the device's hostname) answers it (also multicast, so all devices can update their caches). My goal was to make various devices on my home network accessible over their mDNS address. This works unreliably out of the box, I've collected the steps I took to get it working more reliably.

	MDNS is easily conflated with DNS service discovery (DNS-SD), which allows discovering specific services (e.g. print service, web server, etc.) once a host is known. Both are relevant, however technically these are two separate concepts under Zeroconf.		MDNS is easily conflated with DNS service discovery (DNS-SD), which allows discovering specific services (e.g. print service, web server, etc.) once a host is known. Both are relevant, however technically these are two separate concepts under Zeroconf.
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	To get a more or less complete list of DNS-SD services on the network, use the command <code>avahi-browse --resolve --terminate --all</code>. This uses both mDNS and DNS-SD via the Avahi daemon. For more details, see https://askubuntu.com/a/1105895.		To get a more or less complete list of DNS-SD services on the network, use the command <code>avahi-browse --resolve --terminate --all</code>. This uses both mDNS and DNS-SD via the Avahi daemon. For more details, see https://askubuntu.com/a/1105895.

	To use mDNS to resolve a hostname, use <code>avahi-resolve-host-name <name>.local</code>. This returns only a single resolved address, even if the host has multiple. To at least reliably get an IPv4 or an IPv6 address, pass <code>-4</code> or <code>-6</code>.		To use mDNS to resolve a hostname, use <code>avahi-resolve-host-name <name>.local</code>. This returns only a single resolved address, even if the host has multiple. To at least reliably get an IPv4 or an IPv6 address, pass <code>-4</code> or <code>-6</code>. Alternatively, an purpose-built app that bundles the binary would work. Either approach would of course conflict with the built-in mdnsd if it ever starts, as both listen on port 5353.

	== Becoming Discoverable ==		== Becoming Discoverable ==
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	=== Android ===		=== Android ===

	Support is poor: the address is hard-coded to <code>Android.local</code> and the daemon only starts if some service is ~~registered~~.		Support for responding to mDNS queries on Android devices [https://android.stackexchange.com/a/242004 is poor]. A daemon <code>mdnsd</code> exists, but the address is hard-coded to <code>Android.local</code> and the daemon only starts if an app registers some service.

			One idea [https://stackoverflow.com/a/70343905 is to patch mdnsd] to make the advertized hostname configurable, then run the binary at startup with Termux:Boot. But given the general direction of Android, the chance that this stops working in a future update [https://github.com/termux/termux-app/issues/2155 is always high].

	== Discovering Others ==		== Discovering Others ==
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	On my system, <code>nsswitch.conf</code> is managed by authselect (<code>man(8) authselect</code>, <code>man(5) authselect-profiles</code>). From <code>authselect current</code>, the current profile is called <code>local</code>, while <code>authselect list-features local</code> lists the available feature <code>with-mdns6</code>. Enabling the feature with <code>authselect enable-feature with-mdns6</code> makes the appropriate change to <code>nsswitch.conf</code>.		On my system, <code>nsswitch.conf</code> is managed by authselect (<code>man(8) authselect</code>, <code>man(5) authselect-profiles</code>). From <code>authselect current</code>, the current profile is called <code>local</code>, while <code>authselect list-features local</code> lists the available feature <code>with-mdns6</code>. Enabling the feature with <code>authselect enable-feature with-mdns6</code> makes the appropriate change to <code>nsswitch.conf</code>.

			To check that the change worked, we should find some host that advertises an IPv6 address ([[#Analyzing the Network]]). Then we can use <code>getent ahosts <name>.local</code>, which should return that IPv6 addresses. Unlike the Avahi browse/resolve tools, <code>getent</code> consults the NSS and should thus be indicative of what a normal application sees when making DNS queries.

	==== Caveat on IPv6 Support ====		==== Caveat on IPv6 Support ====
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	Indeed, the only hosts advertising an IPv6 address on my home network are my Linux laptop and my Linux server. However, by using the <code>libnss_mdns_minimal</code> libraries, non-mDNS addresses will by immediately rejected, so that the timeout won't affect us when not resolving mDNS addresses.		Indeed, the only hosts advertising an IPv6 address on my home network are my Linux laptop and my Linux server. However, by using the <code>libnss_mdns_minimal</code> libraries, non-mDNS addresses will by immediately rejected, so that the timeout won't affect us when not resolving mDNS addresses.

	== ~~mDNS and~~ Android ==		=== Android ===

	~~As of November 2021, Android supports resolving mDNS addresses directly.~~
	~~https://source.android.com/docs/core/ota/modular-system/dns-resolver#mdns-local-resolution~~

	https://~~old~~.~~reddit~~.com/r/~~synology~~/~~comments~~/~~sk8dzz~~/~~cannot_ping_mdns_address_servernamelocal_on/hvk0v5k~~/		Unlike the poor support for ''responding'' to queries, Android [https://source.android.com/docs/core/ota/modular-system/dns-resolver#mdns-local-resolution supports resolving mDNS addresses directly] as of November 2021. This should be transparent to applications, as it is built in to <code>getaddrinfo()</code>.

Mxl at 07:57, 20 February 2026

2026-02-20T07:57:00Z

← Older revision		Revision as of 07:57, 20 February 2026
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	== Discovering Others ==		== Discovering Others ==

	=== Avahi ~~(Linux~~) ===		=== Linux (Avahi/NSS) ===

	~~With Avahi installed,~~ mDNS addresses ~~can be resolved~~. Multicast DNS is ~~separate~~ from plain DNS, and ~~will be used by typical applications if~~ enabled by ~~an appropriate~~ entry under <code>hosts:</code> in <code>/etc/nsswitch.conf</code>. On my Fedora system, this contains <code>mdns4_minimal [NOTFOUND=return]</code>, which means mDNS is consulted over IPv4.		Resolution of mDNS addresses on Linux is provided by Avahi via a plugin to the Nameserver Switch (NSS). Multicast DNS is distinct from plain DNS, and is thus enabled by its own entry under <code>hosts:</code> in <code>/etc/nsswitch.conf</code>. On my Fedora system, this contains <code>mdns4_minimal [NOTFOUND=return]</code>, which means mDNS is consulted over IPv4. Most applications will consult the NSS (via glibc) and thus be able to resolve <code>.local</code> addresses.

	As a matter of principle, I would also like mDNS over IPv6 to ~~run~~. Consulting <code>man(5) nsswitch.conf</code>, additional services are implemented as shared libraries named <code>libnss_SERVICE.so.X</code>. Looking in the appropriate places (<code>man(8) ldconfig</code>), we can list available services:		As a matter of principle, I would also like mDNS over IPv6. This can be accomplished by changing <code>mdns4_minimal [NOTFOUND=return]</code> to <code>mdns_minimal [NOTFOUND=return]</code>, which tries both IPv6 and IPv4.

			On my system, <code>nsswitch.conf</code> is managed by authselect (<code>man(8) authselect</code>, <code>man(5) authselect-profiles</code>). From <code>authselect current</code>, the current profile is called <code>local</code>, while <code>authselect list-features local</code> lists the available feature <code>with-mdns6</code>. Enabling the feature with <code>authselect enable-feature with-mdns6</code> makes the appropriate change to <code>nsswitch.conf</code>.

			==== Caveat on IPv6 Support ====

			Consulting <code>man(5) nsswitch.conf</code>, additional services are implemented as shared libraries named <code>libnss_SERVICE.so.X</code>. Looking in the appropriate places (<code>man(8) ldconfig</code>), we can list available services:

	find /lib/ /lib64/ /usr/lib/ /usr/lib64/ -name 'libnss_.so.' -print0		find /lib/ /lib64/ /usr/lib/ /usr/lib64/ -name 'libnss_.so.' -print0
	\| xargs --null basename --multiple \| sort \| uniq		\| xargs --null basename --multiple \| sort \| uniq

			Among other things, this finds the library <code>/lib64/libnss_mdns4.so.2</code> which on my system is provided by the package [https://github.com/avahi/nss-mdns nss-mdns]. From the README, IPv6 support is as simple as changing <code>mdns4_minimal</code> to <code>mdns_minimal</code>.

			However, it comes with the following warning:

			<blockquote>
			Due to the fact that most mDNS responders only register local IPv4 addresses via mDNS, most people will want to use <code>libnss_mdns4.so.2</code> exclusively. Using <code>libnss_mdns.so.2</code> or <code>libnss_mdns6.so.2</code> in such a situation causes long timeouts when resolving hosts since most modern Unix/Linux applications check for IPv6 addresses first, followed by a lookup for IPv4.
			</blockquote>

			Indeed, the only hosts advertising an IPv6 address on my home network are my Linux laptop and my Linux server. However, by using the <code>libnss_mdns_minimal</code> libraries, non-mDNS addresses will by immediately rejected, so that the timeout won't affect us when not resolving mDNS addresses.

	== mDNS and Android ==		== mDNS and Android ==

Mxl at 07:23, 20 February 2026

2026-02-20T07:23:24Z

← Older revision		Revision as of 07:23, 20 February 2026
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	== Becoming Discoverable ==		== Becoming Discoverable ==

	While some devices are easily accessible, some need more work.		While some devices are easily made accessible to mDNS queries, some need more work.

	=== Avahi (Linux) ===		=== Avahi (Linux) ===
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	=== Android ===		=== Android ===

	~~https~~:/~~/source.android~~.~~com/docs/core/ota/modular-system/dns-resolver#mdns-local-resolution~~		Support is poor: the address is hard-coded to <code>Android.local</code> and the daemon only starts if some service is registered.

	~~https://old.reddit.com/r/synology/comments/sk8dzz/cannot_ping_mdns_address_servernamelocal_on/hvk0v5k/~~		== Discovering Others ==

	~~As of Android 12, there is support for mDNS.~~		=== Avahi (Linux) ===

	== mDNS and ~~IPv6 =~~=		With Avahi installed, mDNS addresses can be resolved. Multicast DNS is separate from plain DNS, and will be used by typical applications if enabled by an appropriate entry under <code>hosts:</code> in <code>/etc/nsswitch.conf</code>. On my Fedora system, this contains <code>mdns4_minimal [NOTFOUND=return]</code>, which means mDNS is consulted over IPv4.

			As a matter of principle, I would also like mDNS over IPv6 to run. Consulting <code>man(5) nsswitch.conf</code>, additional services are implemented as shared libraries named <code>libnss_SERVICE.so.X</code>. Looking in the appropriate places (<code>man(8) ldconfig</code>), we can list available services:

			find /lib/ /lib64/ /usr/lib/ /usr/lib64/ -name 'libnss_.so.' -print0
			\| xargs --null basename --multiple \| sort \| uniq

	== mDNS and Android ==		== mDNS and Android ==

	As of ~~Android 12~~, Android supports mDNS ~~to some extent~~.		As of November 2021, Android supports resolving mDNS addresses directly.
			https://source.android.com/docs/core/ota/modular-system/dns-resolver#mdns-local-resolution

	~~== Sources ==~~		https://old.reddit.com/r/synology/comments/sk8dzz/cannot_ping_mdns_address_servernamelocal_on/hvk0v5k/

	https://~~askubuntu~~.com/a/~~1105895~~/~~254818~~

Mxl: Created page with "[https://en.wikipedia.org/wiki/Zero-configuration_networking Zeroconf] consists of a number of related concepts with the common objective of making simple networked services "just work". Initially it was implemented by Apple as Bonjour, but on Linux the re-implementation [https://en.wikipedia.org/wiki/Avahi_(software) Avahi] is usually used to provide Zeroconf. Although initially intended for discovering networked devices like printers or speakers, it can also be useful..."

2026-02-20T06:27:52Z

Created page with "[https://en.wikipedia.org/wiki/Zero-configuration_networking Zeroconf] consists of a number of related concepts with the common objective of making simple networked services "just work". Initially it was implemented by Apple as Bonjour, but on Linux the re-implementation [https://en.wikipedia.org/wiki/Avahi_(software) Avahi] is usually used to provide Zeroconf. Although initially intended for discovering networked devices like printers or speakers, it can also be useful..."

New page

[https://en.wikipedia.org/wiki/Zero-configuration_networking Zeroconf] consists of a number of related concepts with the common objective of making simple networked services "just work". Initially it was implemented by Apple as Bonjour, but on Linux the re-implementation [https://en.wikipedia.org/wiki/Avahi_(software) Avahi] is usually used to provide Zeroconf. Although initially intended for discovering networked devices like printers or speakers, it can also be useful for accessing other hosts or smart home devices on the local network without hard-coding their address or hosting a name server.

The relevant concept in Zeroconf that makes this work is multicast DNS (mDNS) which can resolve hostnames inside a local network by using multicast broadcasts. The mDNS client sends a multicast broadcast asking for <code><name>.local</code>, and the host with the given name (typically the device's hostname) answers it. My goal was to make various devices on my home network accessible over their mDNS address. This works unreliably out of the box, I've collected the steps I took to get it working more reliably.

MDNS is easily conflated with DNS service discovery (DNS-SD), which allows discovering specific services (e.g. print service, web server, etc.) once a host is known. Both are relevant, however technically these are two separate concepts under Zeroconf.

== Analyzing the Network ==

To get a more or less complete list of DNS-SD services on the network, use the command <code>avahi-browse --resolve --terminate --all</code>. This uses both mDNS and DNS-SD via the Avahi daemon. For more details, see https://askubuntu.com/a/1105895.

To use mDNS to resolve a hostname, use <code>avahi-resolve-host-name <name>.local</code>. This returns only a single resolved address, even if the host has multiple. To at least reliably get an IPv4 or an IPv6 address, pass <code>-4</code> or <code>-6</code>.

== Becoming Discoverable ==

While some devices are easily accessible, some need more work.

=== Avahi (Linux) ===

The Avahi Daemon, as typically configured on Linux distributions, does not answer mDNS queries, because it is not configured to provide any services. To publish a "workstation" service, effectively advertising only that the host exists, a change is required in the config file (probably <code>/etc/avahi/avahi-daemon.conf</code>):

publish-workstation=yes

This [https://superuser.com/a/1311455 supposedly used to be the default] in earlier versions, but was changed for security reasons. Using a firewall on untrusted networks is a good idea anyway!

Restart the Daemon afterwards with <code>sudo systemctl restart avahi-daemon.service</code>.

=== Android ===

https://source.android.com/docs/core/ota/modular-system/dns-resolver#mdns-local-resolution

https://old.reddit.com/r/synology/comments/sk8dzz/cannot_ping_mdns_address_servernamelocal_on/hvk0v5k/

As of Android 12, there is support for mDNS.

== mDNS and IPv6 ==

== mDNS and Android ==

As of Android 12, Android supports mDNS to some extent.

== Sources ==

https://askubuntu.com/a/1105895/254818