DNS

A DNS server allows the client to resolve Internet host names without manually configuring DNS addresses.

This page describes popular open source DNS server with highlighted features

Reset systemd-resolved

1. Update /etc/systemd/resolved.conf
    [Resolve]
    DNS=192.168.1.1 8.8.8.8
    FallbackDNS=8.8.4.4

2. Restart system resolved: service systemd-resolved restart

3. Run systemd-resolve --status (or resolvectl status in newer versions of systemd). The output should look like this:
    Global
             DNS Servers: 1.1.1.1
                          8.8.8.8
    ...
4. Run resolvectl dns
Global: 8.8.8.8
...
Link 2 (interface): 192.168.1.1 8.8.8.8 8.8.4.4

** Make sure right symbolic link /etc/resolv.conf -> /run/systemd/resolve/resolv.conf
5. sudo rm -f /etc/resolv.conf && sudo ln -sv /run/systemd/resolve/resolv.conf /etc/resolv.conf

Teminology in DNS

•   An authoritative name server is for publishing the addresses of public servers. If you have an internet-facing server such as a Web, mail or FTP server, then somewhere there is an authoritative server that advertises their IP addresses and names. This may be an authoritative DNS (domain name services) server on your premises, or managed by a third party like your Internet service provider or a hosting service. You can query any public server with the dig command to see how its name and IP address are matched up:

$ dig +nocmd www.linux.com +noall +answer
www.linux.com.  5276 IN  A  140.211.169.7 

• A dns cache is a local copy of the addresses of sites you have visited. This speeds up your network performance because network applications don’t have to wait for DNS queries to be answered by remote servers
• A recursive name server is the one that looks up the address of sites you want to visit. Recursive and cache functions are often combined in the same server, Google Public DNS and OpenDNS are recursive and caching servers.