LDAP over SSL (LDAPS) uses port 636 to provide secure, encrypted authentication for directory services.
Breakdown of Options:
A). SMTP (Simple Mail Transfer Protocol) - Uses port 25, not 636.
B). Syslog - Uses port 514 (UDP), not 636.
C). TFTP (Trivial File Transfer Protocol) - Uses port 69 (UDP), not 636.
D). LDAPS (Lightweight Directory Access Protocol Secure) - # Correct answer. Uses port 636 for secure directory authentication.
Reference:
CompTIA Network+ (N10-009) Official Study Guide - Domain 3.1: Compare and contrast network protocols.
RFC 4511: Lightweight Directory Access Protocol (LDAP)