are there any diagnostic tools to help me figure out how the system is trying (and failing) to do DNS resolution? Ideally something that says "I'm using systemd-resolved or dnsmasq or whatever, and I'm trying to contact server x.x.x.x"

Bonus points for telling me if we're trying to do IPv4 or IPv6 resolution.


So here's the problem I'm trying to solve:

chris@mu:~$ dig dl.google.com

; <<>> DiG 9.11.3-1ubuntu1.1-Ubuntu <<>> dl.google.com
;; global options: +cmd
;; connection timed out; no servers could be reached

What I'm trying to figure out here is:

  1. What service is being asked to resolve the DNS lookup for me. It seems that it could be systemd-resolved, or dnsmasq or resolvconf (and I'm not even sure if that last one is a DNS resolver). This is important because it would tell me what configurations I should be looking at.
  2. What "upstream" DNS servers are being queried. That should come out of the configuration stuff, but I'd like to be able to confirm.

Hello I think this may be half of your question,

plutes@plutes-Lenovo-G50-30:~$ dig https://askubuntu.com

; <<>> DiG 9.11.3-1ubuntu1.1-Ubuntu <<>> https://askubuntu.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 35615
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

; EDNS: version: 0, flags:; udp: 65494
;https://askubuntu.com.     IN  A

;; Query time: 176 msec
;; WHEN: Sun Jun 17 20:21:07 BST 2018
;; MSG SIZE  rcvd: 50

when I issue the dig command this seems to be on the right track. also you could try a whois with the domain name or this browser tool, https://mxtoolbox.com/.

if you do command man dig there is plenty more options with dig.

Hope this helps you out. I think if you use wireshark you can record the packets of the DNS query's

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