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 dcn-colo-251-35.dcn.davis.ca.us is not the root of its zone.
Instead, try zone transfer on dcn.davis.ca.us .
Instead, try zone transfer on dcn.davis.ca.us .