Changes since SOA version
IXFR is a zone transfer request that returns changes since a specific SOA version. Enter the SOA version to request changes since then.
Not an apex domain
The domain auth1.dns.techfak.uni-bielefeld.de is not the root of its zone.
Instead, try zone transfer on techfak.uni-bielefeld.de .
Instead, try zone transfer on techfak.uni-bielefeld.de .