Clear install 4.3.2 system's (Master+Slave), join not work (TLS)

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little addendum …

I check the possible sources of error here:

Requirements for a successful join into the UCS domain

After the installation of a (non-master) UCS system the next step is to join the system into the UCS domain. There are several requirements in order to successfully join a system. All these requirements are checked before the actual join during the installation/setup or the manual join via the Univention Mangement Console (UMC). If these checks fail, the join is aborted. Normally a re-installation is not necessary, just fix the problem and try to join again (as root via the UMC → “Domain Join”…

root@saturn:~# host -t SRV "_domaincontroller_master._tcp.peka.lan"
_domaincontroller_master._tcp.peka.lan has SRV record 0 0 0 tux.peka.lan.

oot@saturn:~# ssh Administrator@tux.peka.lan
Password: 
Univention DC Master 4.3-2:

root@saturn:~# ucr search --brief nameserver
nameserver/external: <empty>
nameserver/option/timeout: 2
nameserver1: 192.168.100.11
nameserver2: <empty>
nameserver3: <empty>