Some months ago I upgraded my CentOS servers from version 5.4 to 5.5. One of these servers were running LDAP Master and LDAP Slave as playground. Although after the upgrade to CentOS 5.5 it was broken, but due to other priorities I didn't had a change to fix it.
On my systems I enabled TLS to communicate to LDAP-servers and also enabled kerberos. So this results in a modified /etc/sysconfig/ldap:
# Enable Kerberos
But I noticed that the RPM installed a new version of that, although with the extension .rpmnew. So after applying the changes that were in the .rpmnew file and when I set SLAPD_LDAPS and SLAPD_LDAPI to "yes" I end up with the following content:
# Parameters to ulimit called right before starting slapd
# - use this to change system limits for slapd
# How long to wait between sending slapd TERM and KILL
# signals when stopping slapd by init script
# - format is the same as used when calling sleep
# By default only listening on ldap:/// is turned on.
# If you want to change listening options for slapd,
# set following three variables to yes or no
And guess what... It works again