DNS Cheatsheet / Resolveping

For Ubuntu Linux

DNS Check

http://www.intodns.com

Get DNS Configuration / Show nameservers

• systemd-resolve --status --no-pager

• cat /etc/resolv.conf

• nslookup orf.at

Flush DNS Cache

• systemd-resolve --flush-caches

DNS Traceroute

• dig -trace xxx.example.com

Query a nameserver

• dig @192.168.0.10 somehost.example.com

Test for closed DNS UDP port (53)

With dig, and mrt (mtr combines the functionality of the traceroute and ping programs in a single network diagnostic tool)

• UDP (default)
  • dig @your.nameserver a-host.in.your.zone
  • mtr -n -r -c 10 -u -P 53 1.2.3.4
• TCP
  • dig @your.nameserver a-host.in.your.zone +tcp
  • mtr -n -r -c 10 -T -P 53 1.2.3.4

Zone TTLs

• 2022052500 serial

  10800 time to refresh 3h

  3600 time to retry

  604800 time to expire
  
  28800 minimum ttl   7,7h