LDAP or Lightweight Directory Access Protocol is a protocol used to provide open and standard access for directory information like users, file shares, permissions, etc. LDAP is created by the IETF as an open standard and different RFCs are created to explain details of the LDAP protocol. The LDAPS is the secured version of the LDAP protocol where the LDAP communication is simply encrypted. The LDAP and LDAPS use different port numbers for the server connection. LDAP uses port number 389 and LDAPS uses port number 636.
LDAP Port Number 389
LDAP uses port number 389 by default where this port number can be changed according to the situation. But by default, most of the LDAP servers or services use port number 389 in order to make the LDAP services available to all users in a standard way.
LDAPS Port Number 636
LDAPS is the secure version of the LDAP protocol where the LDAP connection is encrypted during network transmission. There TLS/SSL protocol is used to encrypt LDAP communication Actually the LDAPv3TLS extension is created and added to the LDAP protocol to make LDAPS compatible with the original LDAP protocol. The LDAPS work on port number 636. Actually, the LDAPS protocol communication starts as LDAP with the port number 389 but after initial stems the StartTLS mode is enabled and the communication is encrypted and transferred to port number 636.