https://bugs.openldap.org/show_bug.cgi?id=9318
--- Comment #1 from Ryan Tandy ryan@openldap.org --- The very same RFC says, in section 1.4 (Applicability):
This document also does not supersede the rules for verifying service identity provided in specifications for existing application protocols published prior to this document, such as those excerpted under Appendix B.
For LDAP, RFC 2830 (excerpted in the appendix as mentioned) is the relevant specification, which 6125 explicitly says it does NOT supersede.