17.1 Protocol Principle

The LDAP is of the client-server protocol type. The client connects to the server (a well-known port is 389/TCP) and then sends requests in Protocol Data Units (PDU) that have ASN.1 syntax and are encoded in BER (Basic Encoding Rules). The server accepts the request, performs the requested operation, and returns results. Communication between the server and the client need not be synchronous, and the client and the server must be able to work in asynchronous mode (for example, the client does not have to wait for a reply for a sent request before sending further requests). The processing of a pending request can be terminated by the abandon command. The LDAP protocol also allows client authentication.

Note

The communication protocols described earlier were communicating in a text form. This is why we have been able to simulate the communication with the help of the Telnet program. In contrast, the LDAP’s protocol data units are binary (BER encoded). Hence...