{{DISPLAYTITLE:mDNS}}
[https://en.wikipedia.org/wiki/Multicast_DNS Multicast DNS] is a protocol that is normally used for the discovery of printers. Avahi is a popular implementation by but more setup is needed for the regular name resolution to see the results.

{{warning|The might be in issue in ipv4/ipv6 dual-setups. [https://github.com/LouisBrunner/avahi2dns/issues/21 Check this issue.]}}

== Setup avahi ==

Install, enable and start avahi with:

{{cmd|doas apk add {{pkg|avahi}}
doas rc-update add avahi-daemon
doas rc-service avahi-daemon start}}

It should now be possible to browse results. To look for a printer, use:

{{cmd|doas apk add {{pkg|avahi-tools}}
avahi-browse --resolve --terminate _ipp._tcp}}

Make note of the hostname, as we will use it afterwards.

== Setup avahi2dns ==

Name resolution is implemented by musl, and it only supports DNS, so we have to map the avahi results to a regular DNS server. This is done by avahi2dns.

{{cmd|doas apk add {{pkg|avahi2dns}}}}

since we will want a full DNS server running at port 53, we need to configure avahi2dns to use another port. This is done by default with {{path|/etc/conf.d/avahi2dns}} containing:

command_args="-p 5354"

Enable and start avahi2dns with

{{cmd|doas rc-update add avahi2dns
doas rc-service avahi2dns start}}

It should now be possible to use DNS to query the address of the printer.

{{cmd|drill -p 5354 @127.0.0.1 <printer_name>.local}}

Where printer_name is the hostname given by avahi-browse.

== Setup Networkmanager ==

If you are already using networkmanager, you can leverage {{pkg|dnsmasq}} as your DNS server which can easily forward mDNS requests to another server.

Install the {{pkg|networkmanager-dnsmasq}} package:

{{cmd|doas apk add {{pkg|networkmanager-dnsmasq}}}}

Configure networkmanager to use dnsmasq as it's dns server by editing {{path|/etc/NetworkManager/NetworkManager.conf}}

[main]
dhcp=internal
dns=dnsmasq

Then we need to tell dnsmasq to forward all mDNS queries to avahidns {{path|/etc/NetworkManager/dnsmasq.d/mdns.conf}}:

# Forward queries for the "local" domain to 127.0.0.1 port 5354
server=/local/127.0.0.1#5354

Restart networkmanager:

{{cmd|doas rc-service networkmanager restart}}

== Without NetworkManager ==

=== Setup DNS resolver ===

If you are not using NetworkManager, you will need to setup a DNS resolver that will forward request of .local domain to avahi2dns and handle other requests normally. There is more than one way to do it, but we document an option that is probably most convenient for a laptop: using the DHCP provided server for the regular DNS requests. We will use unbound as the server and resolvconf to inform unbound about the DHCP results.

Install the programs:

{{cmd|doas apk add {{pkg|openresolv}} {{pkg|unbound}}}}

Create {{path|/etc/resolvconf.conf}}:

name_servers=127.0.0.1
unbound_conf=/etc/unbound/unbound.conf.d/resolvconf.conf

This tells resolveconf to use a local nameserver and pass the DHCP provided DNS server to unbound

Create {{path|/etc/unbound/unbound.conf.d/avahi-local.conf}}:

forward-zone:
name: "local"
forward-addr: 127.0.0.1@5354
server:
do-not-query-localhost: no
domain-insecure: "local"

This reads the information provided by resolvconf, but forwards .local requests to avahi2dns. We also need to disable dnssec for .local and tell unbound that it is OK to query localhost.

Enable and start unbound

{{cmd|doas rc-update add unbound
doas rc-service unbound start}}

=== Using bind(named) as DNS resolver ===

It is assumed that bind(named) is already installed and running, if not, then you can use the instructions[[https://wiki.alpinelinux.org/wiki/Small-Time_DNS_with_BIND9]]

If you already have a bind(named) server configured, then the solution is to set an access "zone" for postfix addresses.local

To do this, add the following lines to the bind configuration file (by default, the /etc/bind/named.conf file is used):

zone "local" {
type forward; # type requests
forward only; # rule to use only forwards
forwarders {
127.0.0.1 port 5354; # Avahi2dns adress and port
};
};

Additionally, you may need to disable dnssec verification for the .local postfix. To do this, add the following lines inside the options configuration:

options {
...
validate-except {
"local";
};
...
};

After adding the configuration, double-check that you have a .local zone. To do this, use the command:

named-checkconf -l # OUTPUT: local IN _default forward

If there were no errors, you can reload the bind(named) service:

rc-service named reload

=== Setup DHCP client ===

How send the DHCP provided DNS to resolvconf depends on the DHCP client being used.

==== udhcpc ====

This is the DHCP client in busybox, and will work for both wired and wireless interfaces.

Create {{path|/etc/udhcpc/udhcpc.conf}}:

RESOLV_CONF="/etc/udhcpc-resolv.conf"

Create {{path|/etc/udhcpc/post-bound/resolvconf}}:

#!/bin/sh
cat /etc/udhcpc-resolv.conf | resolvconf -a $interface

and make it executable

{{cmd|chmod 755 /etc/udhcpc/post-bound/resolvconf}}

An inconvenience of this setup is that udhcpc will not reconfigure the interface when connecting to other wifi networks. For that to happen one has to run

{{cmd|iwctl station wlan0 connect <network_name>
doas kill -USR2 $(cat /run/udhcpc.wlan0.pid)
doas kill -USR1 $(cat /run/udhcpc.wlan0.pid)}}

==== iwd ====

To avoid having to manually reconfigure the wifi interface, we can configure iwd to use DHCP internally and forward DNS server info to resolveconf. To do that create {{path|/etc/iwd/main.conf}}:

[General]
EnableNetworkConfiguration=True

[Network]
NameResolvingService=resolvconf

== Test the setup ==

You should now be able to query for both the printer address and regular addresses with

{{cmd|drill @127.0.0.1 <printer_name>.local
drill @127.0.0.1 alpinelinux.org}}

Your {{path|/etc/resolv.conf}} should also contain

nameserver 127.0.0.1

Printer discovery should now be working.

[[Category:Networking]]