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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.

EDIT/CLARIFICATION:

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.
0

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

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

;; Query time: 176 msec
;; SERVER: 127.0.0.53#53(127.0.0.53)
;; 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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