2025-09-28:
Local decentralized DNS without DNS: Multicast DNS (mDNS)
Entering
You have two linux items (others will also work, but you'll need to google why) that you want to communicate between.
The simplest way is to use ip, but only once. Tommorow the item will get a different ip, you can't win it.
The simplest way is to add an alias into /etc/hosts
192.168.0.48 destination
And use the alias everywhere:
$ scp kitty.gif user@destination:
But the ip will change anyway. But you will update it in a single place. But you will update it.
The simplest way to fix is install local DNS server on the server, make it the main server in the network, and proxy DNS queries throught it there is no.
Wouldn’t it be a breeze to avoid editing by hand?
Multicast DNS (mDNS)
In 2025 year 25 years ago was invented Multicast DNS (mDNS) which via brodcast request creates a local dynamic decentralized DNS that you shouldn't care about. But only within the single network. And only single host per item.
How Multicast DNS (how mDNS)
In linux when it converts word-names into numbers, it uses service Name Service Switch. This service has /etc/nsswitch.conf where it was shown where to how to look:
> cat /etc/nsswitch.conf
# Name Service Switch configuration file.
# See nsswitch.conf(5) for details.
passwd: files systemd
group: files [SUCCESS=merge] systemd
shadow: files systemd
gshadow: files systemd
publickey: files
hosts: mymachines resolve [!UNAVAIL=return] files myhostname dns
networks: files
For "hosts" it says to check first in local containers (mymachines)
Then it go to the (systemd-resolved) dns resolver which replaced nss-dns. If DNS returns unavailable, it quits.
Then it checks /etc/hosts, local hostname, and legacy DNS.
Engaging fact: we can add another service to the list. What if we will add the Multicast DNS (mDNS)?
Multicast DNS installation (mDNS installation)
Oviously, for literaly everyone we will have both and server, and client parts. We will do belows everywhere for harmony.
https://wiki.archlinux.org/title/Avahi
Install package libnss-mdns in deps of which is avahi (we will add into NSS hosts as service):
# pacman -Sy nss-mdns
# emerge -av sys-auth/nss-mdns
# sudo apt-get install libnss-mdns avahi-daemon avahi-utils
Next add to /etc/nsswitch.conf following string mdns_minimal [NOTFOUND=return]:
# hosts: mymachines resolve [!UNAVAIL=return] files myhostname dns
hosts: mymachines mdns_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] files myhostname dns
# hosts: mymachines mdns_minimal resolve [!UNAVAIL=return] files myhostname dns
[NOTFOUND=return] tells not to look for domains*.local anymore, this will break entries in /etc/hosts so you can remove it to keep everything work as before, but better.
You can also catch domains beyond *.local, but we don't need it. We'll use /etc/hosts for it.
Set local domain in the file /etc/avahi/avahi-daemon.conf and reload and check:
$ cat /etc/avahi/avahi-daemon.conf | grep host-name
host-name=source
$ systemctl enable avahi-daemon.service # add to autorun
$ systemctl restart avahi-daemon.service # run
$ avahi-browse --all --verbose --resolve --terminate
$ avahi-resolve-host-name source.local
source.local 192.168.100.101
$ ping source.local
PING source.local 56 data bytes
64 bytes from source.local : icmp_seq=1 ttl=64 time=0.031 ms
64 bytes from source.local : icmp_seq=2 ttl=64 time=0.067 ms
64 bytes from source.local : icmp_seq=3 ttl=64 time=0.056 ms
^C
The problem is that we can have only one domain per item. If you want to have multiple local domains like:
git.local
server.local
You can easily do this via /etc/avahi/hosts, but there you also have to hardcode the ip.
The simplest way to fix it would be to run multiple instances of there is no simple way live with the single domain on it's all better anyway.avahi-publish & per each domain each time calcuting dynamic local ip
Enable sftp/ssh
$ cp /usr/share/doc/avahi/sftp-ssh.service /etc/avahi/services/
$ cp /usr/share/doc/avahi/ssh.service /etc/avahi/services/
$ systemctl restart avahi-daemon.service
Second item
Quickly repeat on the second item, then check from both they aren't alone. Configure an ssh connection by ip between two items. Then in ssh just replace ip to the local domain:
$ ssh my_user@destination.local -i ~/.ssh/my_key
When eveything works we add to ~/.ssh/config magic words:
Host destination
HostName destination.local
IdentityFile ~/.ssh/my_key
User my_user
An alias for ssh was magically created and fully configured:
$ ssh destination
That's all, we can now exchange files and remotely execute commands
$ cd /tmp/
$ date > temp_file
$ echo "source" >> temp_file
$ scp temp_file destination:
$ ssh destination 'echo destination >> ~/temp_file'
$ ssh destination 'cat ~/temp_file'
Uru ru ru, we can now exchange files and remotely execute commands. And now we can use domains not tied to ip!
Leaving
There is no multidomaning on the single item, but I can live with it.
You can apply the same to NFS and rsync and git!!!
And also mDNS the base of IoT and other home assistant networks!