Chicken and egg problem with NTP and Bind

This a report of a problem I solved but I feel the solution could be useful to other. The problem appeared on a Raspbian 9.13. For some - probably hardware - reasons still to be discovered, my Raspberry pi-based router crashed and could not restart. I found it stuck on the raibow like image displayed when the Pi is just powered up. Anyway, I restarted the Pi and everything worked as usual. The only thing that did not work was Bind 9. The daemon was running but names resolution did not work. I had a look at the following help : https://dnsinstitute.com/documentation/dnssec-guide/ch05s04.html because I found weird logs in /var/log/named/dnssec.log : validating ./NS: verify failed due to bad signature (keyid=60955): RRSIG validity period has not begun One possible solution I found was that, indeed, the time was not right : The pi displayed a time a good five hours in the past. Which explained why it found RRSIG validity in the future. Thing is: it could not set its time right because it could not resolve the NTP servers name. Because name resolution did not work at all, because the time was not right.