CUPS synchronizes users from CUCM. CUPS does not sychronize with LDAP.
How about "CUPS Admin > Application > Cisco Unified Personal Communicator > LDAP server"? Well, as the menu inidcated, it's a configuration for CUPC. It's not a configuration for CUPS. CUPC download this configuration upon login and use that to query LDAP (for contact search).
Even though LDAP integration is not configurable on CUPS, it might affect CUPS in an unexpected way.
Scenario 1: CUCM is using LDAP authentication. CUPC user not able to login.
When CUPC users try to login, the username/password was authenticated aginst CUPS (via SOAP). In turn, CUPS will authenticated the username/password against LDAP (because CUCM is using LDAP authentication). If for whatever reason, CUPS having problem with LDAP, authentication would failed.
Reason A: Access-list blocked traffic between CUPS and LDAP. Access-list allow traffic between CUCM and LDAP. Access-list allow traffic between CUPS and CUCM.
In this case, CUPS would synchronize CUCM users over. But those users won't be able to log into CUPC. Because CUPS cannot talk to LDAP.
Reason B: CUCM was configured to use LDAP over SSL (LDAPS). Certificates were uploaded to CUCM but not to CUPS.
In this case, CUPS won't be able to set up the LDAPS connection because the certificates were missing.
Frequently asked questions:
Do I need CUCM/LDAP integration to use CUPS/CUPC?
Answer: No. But there are some catchas. CUCM/LDAP integration is highly recommended.
1) Without LDAP, adding contacts to CUPC would be a pain. Because CUPC cannot search CUCM for contacts. (there's no such a thing called "CUCM native directory")
2) If you use LDAP with CUPC but not CUCM, potential problem is on the way. If you search LDAP from CUPC and add that contact to CUPC contact list, user ID in LDAP would be used as "presence user ID". If the "presence user ID" is different with the user ID in CUCM, you won't be able to see your contact's presence (your contact would always be offline).
1) Make sure the user ID in LDAP matches the user ID in CUCM.
2) If the CUCM ID happens to be the phone extension number. And you happen to have the phone extension number configured in LDAP. You may go to "CUPS Admin > Application > Cisco Unified Personal Communicator > Settings" to map the LDAP phone attribute to the CUPC "user ID" attribute.