[dns-operations] A strange DNS problem (intermittent SERVFAILs)

[Stephane Bortzmeyer]

Several users on Twitter reported problems accessing Banque Populaire
(a French bank) https://www.banquepopulaire.fr
https://www.ibps.loirelyonnais.banquepopulaire.fr
https://www.ibps.bpaca.banquepopulaire.fr
https://www.ibps.mediterranee.banquepopulaire.fr/

>From the limited reports, all errors point to a DNS issue. (For one
user, adding the IP address in /etc/hosts solved the problem.)

But testing with existing resolvers and with the RIPE Atlas probes do
not show a widespread outage.

The existing DNS configuration is clearly very questionable, such as a
zone delegated to just one name server, and a broken one, replying
REFUSED for NS and SOA queries.

The question is "how did this incorrect setup can produce *sometimes*
a resolution failure?"

Details in french, plus dig outputs (not in french) are at
<http://shaarli.guiguishow.info/?F7a6EA>.