mDNS
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.
Setup avahi
Install, enable and start avahi with:
$ doas apk add 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:
$ doas apk add 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. As of now, avahi2dns package is available in the testing repository. It can be safely installed by following the guidelines.
$ doas apk add avahi2dns@testing
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 /etc/conf.d/avahi2dns containing:
command_args="-p 5354"
Enable and start avahi2dns with the command:
$ 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:
$ 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 dnsmasq as your DNS server which can easily forward mDNS requests to another server.
Install the networkmanager-dnsmasq package:
$ doas apk add networkmanager-dnsmasq
Configure networkmanager to use dnsmasq as it's dns server by editing /etc/NetworkManager/NetworkManager.conf as follows
Contents of /etc/NetworkManager/NetworkManager.conf
Then we need to tell dnsmasq to forward all mDNS queries to avahidns by editing the file /etc/NetworkManager/dnsmasq.d/mdns.conf as follows
Contents of /etc/NetworkManager/dnsmasq.d/mdns.conf
Restart networkmanager:
$ doas rc-service networkmanager restart
Without NetworkManager
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.
Setup unbound as DNS resolver
We will use unbound as the server and resolvconf tool to inform unbound about the DHCP results. This option is probably most convenient for a laptop: using the DHCP provided by the server for the regular DNS requests.
Install the programs:
$ doas apk add openresolv unbound
Create /etc/resolvconf.conf as follows:
Contents of /etc/resolvconf.conf
This tells resolveconf to use a local nameserver and pass the DHCP provided DNS server to unbound. Create /etc/unbound/unbound.conf.d/avahi-local.conf as follows
Contents of /etc/unbound/unbound.conf.d/avahi-local.conf
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.
$ doas rc-update add unbound $ doas rc-service unbound start
Using existing bind server as DNS resolver
It is assumed that a bind(named) server is already installed and running, if not, then you can use the instructions Small-Time_DNS_with_BIND9
Once the bind(named) server is up and running, 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 /etc/bind/named.conf as follows
Contents of /etc/bind/named.conf
Additionally, you may need to disable dnssec verification for the .local postfix. To do this, add the following lines inside the options configuration
Contents of /etc/bind/named.conf
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:
$ doas 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 /etc/udhcpc/udhcpc.conf as follows
Create the file /etc/udhcpc/post-bound/resolvconf as follows
Contents of /etc/udhcpc/post-bound/resolvconf
and make it executable
$ doas chmod 755 /etc/udhcpc/post-bound/resolvconf
iwd
When using iwd 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
$ iwctl station wlan0 connect <network_name> $ doas kill -USR2 $(cat /run/udhcpc.wlan0.pid) $ doas kill -USR1 $(cat /run/udhcpc.wlan0.pid)
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 the file /etc/iwd/main.conf as follows
Contents of /etc/iwd/main.conf
Troubleshooting
Test the setup
You should be able to query for both the printer address and regular addresses with:
$ drill @127.0.0.1 <printer_name>.local $ drill @127.0.0.1 alpinelinux.org
Your /etc/resolv.conf should also contain
Contents of /etc/resolv.conf
Printer discovery should now be working.
Failure in parallel query of A and AAAA requsts
An issue with parallel query of A and AAAA requsts was reported to upstream related to ipv4/ipv6 dual-setups and since been resolved in Alpine Linux !82560 by adding a timeout 2.5s.