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Windows application 'LDAP Admin' fails to connect to OpenLDAP on port 636

mw flag

I run an OpenLDAP server on (2.6.3_2) FreeBSD.

I works fine with FreeBSD/Linux clients like PAM/NSS/NextCloud over LDAPS port 636.(With a Let's Encrypt certificate)

I can't get it to work together with Windows 11 and LDAP-Admin 1.8.3.0 unless I open up for LDAP port 389. (I would prefer to keep this potentially unsafe protocol closed)

If I configure LDAP-Admin to use Simple-auth+TLS over port 389, then it works. In Wireshark I can se it initiates an LDAP-StartTLS and then upgrades to TLSv1.3.

If I configure LDAP-Admin to use Simple-auth+TLS over port 636, then it ping-pongs a handful of TLSv1.3 telegrams, and fails with "LDAP Error: Unwillingly to perform"

I cant get my head around why a StartTLS session works, but a session over a dedicated TLS port does not.

Log on server:

ACCEPT from IP=10.0.0.88:56741 (IP=0.0.0.0:636) TLS established
tls_ssf=256 ssf=256 tls_proto=TLSv1.3
tls_cipher=TLS_AES_256_GCM_SHA384 UNBIND
closed

Edit: I have now set 'security ssf=50 update_ssf=128' this should prevent non startTLS on port 389

cn flag
You should be able to use ldp.exe to establish a connection on tcp/636 and see the console output. You can also enable the Windows CAPI2 event log. This will log any errors with certificate trust or CRL/AIA/CDP access. Could also be an incompatible/problematic protocol/cipher. There are other tools for Windows. The most common is Softerra LDAP Browser. https://www.ldapadministrator.com/softerra-ldap-browser.htm
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