[Samba] Joining a samba ad dc domain from another samba installation

[François Legal]

Hello,

I've got a debian Buster machine running samba as AD DC. To upgrade to Bullseye, I installed a new VM, and tried to join the domain as another DC, so that I could then migrate everything using the setup in VM.

Unfortunately, when trying to join the domain, I always get the same error shown below. I tried to increase le log verbosity on both end, but that did not give me a hint on what was going on.

I tried all the authentication options outlined in the wiki with no luck.

Can anybody point me in the right direction.

My samba versions are :
Version 4.9.5-Debian on the current DC [my-dc].[my samba domain]
Version 4.13.13-Debian on the VM that I try to join to the domain.

Oh, I also tried to join the domain as a normal machine, and that failed in the same way.

Thanks in advance

François

samba-tool domain join [my samba domain] DC -k yes --dns-backend=BIND9_DLZ --option='idmap_ldb:use rfc2307 = yes'
INFO 2022-04-25 10:41:04,952 pid:374 /usr/lib/python3/dist-packages/samba/join.py #107: Finding a writeable DC for domain '[my samba domain]'
INFO 2022-04-25 10:41:04,973 pid:374 /usr/lib/python3/dist-packages/samba/join.py #109: Found DC  [my-dc].[my samba domain] 
ERROR(<class 'samba.join.DCJoinException'>): uncaught exception - Can't join, error: 00002020: Operation unavailable without authentication
  File "/usr/lib/python3/dist-packages/samba/netcmd/__init__.py", line 186, in _run
    return self.run(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/samba/netcmd/domain.py", line 661, in run
    join_DC(logger=logger, server=server, creds=creds, lp=lp, domain=domain,
  File "/usr/lib/python3/dist-packages/samba/join.py", line 1536, in join_DC
    ctx = DCJoinContext(logger, server, creds, lp, site, netbios_name,
  File "/usr/lib/python3/dist-packages/samba/join.py", line 121, in __init__
    raise DCJoinException(estr)