Enlisting fails due to it trying to use external DNS servers instead of maas-internal

I am trying to get several servers enlisted into MAAS. It boots, finds ens1f0 and continues loading stuff. After downloading some packages it tries to connect to http://.maas-internal:5248/MAAS/api/2.0/machines/?op=is_registered… But this fails because it is trying to use the upstream DNS servers configured in MAAS instead of the internal DNS server of MAAS.

Any idea what is wrong in my configuration?

Looking at that DHCP configuration, I see:

option domain-name-servers,,;

Comparing this to the tcpdump, I never see the enlisting image trying to access (MAAS) when querying for