Hi @Jan
you need to connect to the proper port so please try:
user@debian:~$ ldapsearch -d8 -H ldaps://ucs-master:7636 -D "cn=$(hostname),cn=computers,dc=domain,dc=tld" -W "cn=$(hostname)"
or
user@debian:~$ ldapsearch -d8 -H ldap://ucs-master:7389 -D "cn=$(hostname),cn=computers,dc=domain,dc=tld" -W "cn=$(hostname)"
If it works you might remove the debugging flag -d8
Keep in mind that you can’t access the whole LDAP directory by a restricted account! Often you’re only allowed to access your own entry.