We noticed intermittent DNS resolution issues. Roughly every second DNS request returned not found for DNS entries on our internal .lan zone. After checking that /etc/resolv.conf indeed contains the correct DNS settings provided by the DHCP server, we suspected it is some kind of caching.

It turns out that openSuse Leap does DNS caching using nscd by default.

Other people have already reported issues with it: https://www.reddit.com/r/openSUSE/comments/s0oq4e/wierd_dns_caching_issue/

The problem was resolved by disabling DNS caching:

1. Set enable-cache hosts no in /etc/nscd.conf
2. Relaunch the nscd daemon sudo systemctl restart nscd