LDAP Port 389 for User Authentication in N10-009
Short answer
B Port 389 is LDAP, the directory service port whose bind operation validates user credentials, making it the option most directly associated with user authentication.
Question
Key Takeaways
It tests mapping well-known ports to service roles; the trap is choosing 443 because browsers handle login pages, even though LDAP is the directory protocol directly tied to credential validation.
This N10-009 port question asks which service is most likely used for user authentication. The answer is B, LDAP over TCP 389, because its bind operation validates directory credentials.
Common mistake: A common wrong choice is C (443), because HTTPS often fronts a login page; however, 443 is generic web transport, while LDAP on 389 is the listed service whose bind operation directly validates user credentials.
Expert Analysis
The authentication path starts with a directory bind. In an LDAP-based login, the client opens TCP 389 to the directory server and sends a BindRequest containing a distinguished name and password. The directory server checks that credential against its directory data and returns a bind result. Only after a successful bind does the application treat the user as authenticated and evaluate authorization. That request-and-response exchange is exactly the user-authentication role being tested, so B (389) is the strongest match.
Why the other ports fail the role check. Port 123 is NTP, which synchronizes clocks and does not authenticate users. Port 587 is SMTP submission, which can carry SMTP AUTH when a client submits mail, but it is a mail-transfer role rather than a directory authentication service. Port 443 is HTTPS; it can protect a browser login form, but the port itself is generic encrypted web transport. Any credential check on 443 is performed by the application behind it, not by the service definition of the port.
What the supplied comment adds. The supplied comment correctly links 389 to LDAP and describes using directory queries for authentication, authorization, and user information. That matches the bind mechanism: authentication happens when the directory validates credentials, while authorization is a later decision based on attributes or group membership. The mention of authorization should not blur the question; the credential-check step is the authentication event.
Trace the alternative to expose the trap. With 443, the client first negotiates TLS, then sends an HTTP request to a web application. That application might query an LDAP directory or a local database behind the scenes. The actual authentication could still occur over 389, but the question asks which listed port is most likely used with user authentication—the service port directly associated with validating user identity. Port 587 similarly allows SMTP AUTH for mail submission, and 123 only synchronizes time.
Exam takeaway. Map each number to its service before choosing: 123=NTP, 389=LDAP, 443=HTTPS, 587=SMTP submission. When the stem says user authentication without describing a browser or mail client, LDAP is the direct directory-authentication answer.
Official Reference
- https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml
- https://www.rfc-editor.org/rfc/rfc4511
- https://www.rfc-editor.org/rfc/rfc4513
These links open the official vendor documentation in a new tab.
Exam Strategy
When a port question mentions authentication, map every option to its service before reading the scenario: 123=NTP, 389=LDAP, 443=HTTPS, 587=SMTP submission. Eliminate services that perform time synchronization or mail transfer, then decide between generic secure web traffic and a directory access protocol. If the stem says user authentication without mentioning a browser, prefer LDAP because its bind operation validates credentials in directory services. Memorize port/protocol pairs as role definitions, not just numbers.
Frequently Asked Questions
Why does LDAP port 389 count as user authentication?
Could HTTPS on port 443 be the answer because web logins use HTTPS?
What are ports 123 and 587 used for in this context?
Discussion 1 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 1
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ERB14 👍 1 Answered BPort 389 (LDAP): This port is used for the Lightweight Directory Access Protocol (LDAP), which is widely used for querying directory services to handle user authentication, authorization, and managing user information within an organization.
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