dns.txt

resolve name to IP

port 53

             zones
       /      /     /
bob.sales.example.com
 |    |      |     +-- top-level domain (on root nameservers)
 |    |      +-- subdomain of com
 |    +-- subdomain of example
 +-- resource record (RR) part of the sales.example.com domain

Zones are defined in zone files on primary nameservers. They contain RRs such as bob.

Authoritative nameservers answer to resource records that are part of their
zones only. Recursive nameservers offer resolution services, but they are not
authoritative for any zone (ie. they don't have direct answers).

BIND
* named: nameserver
* rndc: admin utility
* dig

AWS: cli53

The mechanism for name resolution is decided in:
/etc/nsswitch.conf
hosts files DNS
        |    +-- use DNS servers declared in /etc/resolv.conf (often overwitten by NetworkManager or DHCP)
        +-- /etc/hosts

gotcha: the host command doesn't respect /etc/nsswitch.conf, thus not /etc/hosts either

www.example.com -> 12.34.56.78
web.example.com -> CNAME to www.example.com (~symlink, target must be A/AAAA + not zone apex)
    12.34.56.78 ->   PTR to web.example.com (~reverse link)