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Difficulty: HardCommon Ports and Protocols

A network security administrator is configuring internal perimeter firewall rules to enforce compliance for user directory queries between web application servers and a central domain controller. Company policy mandates that all authentication requests across network segments must be cryptographically encrypted over SSL/TLS, and cleartext directory protocol traffic must be dropped. Which of the following port and transport protocol combinations must be explicitly permitted on the firewall to allow compliant directory services traffic?

  1. TCP port 636Answer
  2. B
    TCP port 389
  3. C
    UDP port 636
  4. D
    TCP port 3268

Answer

TCP port 636 must be permitted on the firewall to allow encrypted LDAP (LDAPS) traffic.
Lightweight Directory Access Protocol Secure (LDAPS) uses TCP port 636 to establish an encrypted TLS/SSL tunnel for directory queries and user authentication. This satisfies the requirement to encrypt all identity queries and block unencrypted traffic.

Step-by-Step Solution

1
Identify the service and security requirements
The scenario requires directory access services (LDAP family) protected by SSL/TLS encryption.
Compliance policy mandates encrypted authentication queries and prohibits cleartext directory communications.
2
Differentiate unencrypted vs. encrypted directory port assignments
Standard cleartext LDAP uses TCP port 389, while Lightweight Directory Access Protocol Secure (LDAPS) uses TCP port 636.
Port 636 is the default port reserved for LDAP session negotiations wrapped within TLS/SSL.
3
Determine the appropriate transport layer protocol
TCP is selected over UDP because TLS/SSL encryption handshakes require reliable, connection-oriented communication.
Connection-oriented TCP guarantees packet delivery and state tracking required for secure session management.

Key Concept

Lightweight Directory Access Protocol Secure (LDAPS) Port and Transport Identification
Estimated Time:1m 30s
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Topics

Common Ports and Protocols

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