DNS delay on first lookup, Ubuntu 19.10 but not earlier versions

[Chris Green]

On Wed, Apr 01, 2020 at 08:51:15PM +1100, Karl Auer wrote:
> On Wed, 2020-04-01 at 10:41 +0100, Chris Green wrote:
> > zbmc.eu is the local domain.  All systems on the LAN register (using
> > DHCP) with the Pi so it knows about all the systems on the LAN.  The
> > bug only affects my two systems running xubuntu 19.10, all other
> > systems (Debian, xubuntu 18.04, MS Windows) work with no delay.
> 
> zbmc.eu is also a real domain in the global DNS.
> 
> What are you doing that causes the lookups? A browser, dig, something
> else?
> 
> It is possible that your newer systems are using DOH (DHCP over HTTP);
> another possibility is that they are using IPv6 a little differently.
> 
> From one old and one new system please post the output of "dig
> esprimo.zbmc.eu"...
> 
No difference (but 'dig' doesn't show a delay), here's a 'dig'
followed by a 'host' immediately after reboot on one of the systems
that shows the delay:-

    chris$ time dig esprimo.zbmc.eu

    ; <<>> DiG 9.11.5-P4-5.1ubuntu2.1-Ubuntu <<>> esprimo.zbmc.eu
    ;; global options: +cmd
    ;; Got answer:
    ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 46141
    ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

    ;; OPT PSEUDOSECTION:
    ; EDNS: version: 0, flags:; udp: 65494
    ;; QUESTION SECTION:
    ;esprimo.zbmc.eu.               IN      A

    ;; ANSWER SECTION:
    esprimo.zbmc.eu.        0       IN      A       192.168.1.3

    ;; Query time: 3 msec
    ;; SERVER: 127.0.0.53#53(127.0.0.53)
    ;; WHEN: Wed Apr 01 11:10:14 BST 2020
    ;; MSG SIZE  rcvd: 60


    real    0m0.013s
    user    0m0.004s
    sys     0m0.005s
    chris$ time host esprimo.zbmc.eu
    esprimo.zbmc.eu has address 192.168.1.3

    real    0m10.018s
    user    0m0.000s
    sys     0m0.010s


... and here's a dig from an Ubuntu 18.04 system:-

    chris at backup$ dig esprimo.co.uk

    ; <<>> DiG 9.11.3-1ubuntu1.11-Ubuntu <<>> esprimo.co.uk
    ;; global options: +cmd
    ;; Got answer:
    ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 32618
    ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

    ;; OPT PSEUDOSECTION:
    ; EDNS: version: 0, flags:; udp: 65494
    ;; QUESTION SECTION:
    ;esprimo.co.uk.                 IN      A

    ;; Query time: 18 msec
    ;; SERVER: 127.0.0.53#53(127.0.0.53)
    ;; WHEN: Wed Apr 01 11:11:09 BST 2020
    ;; MSG SIZE  rcvd: 42



-- 
Chris Green