I found log in ldap.log file
Apr 12 14:20:54 abc slapd[3136]: => access_allowed: auth access to
"uid=bobliu,ou=it,dc=abc,dc=com" "userPassword" requested
Apr 12 14:20:54 abc slapd[3136]: => slap_access_allowed: backend default
auth access granted to "(anonymous)"
Apr 12 14:20:54 abc slapd[3136]: => access_allowed: auth access granted
by read(=rscxd)
Apr 12 14:20:54 abc slapd[3136]: => access_allowed: backend default
write access denied to "uid=bobliu,ou=it,dc=abc,dc=com"
why access granted to anoymous not bobliu.