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Difficulty: MediumCommon Ports and Protocols

An enterprise network administrator notices that user authentication attempts using Kerberos are failing across multiple branch offices due to time skew between client workstations and domain controllers. To ensure automated clock synchronization across the network, which transport protocol and destination port must be permitted on the network firewalls?

  1. UDP port 123Answer
  2. B
    TCP port 123
  3. C
    UDP port 161
  4. D
    TCP port 514

Answer

UDP port 123 is required to allow Network Time Protocol (NTP) traffic for network-wide time synchronization.
Network Time Protocol (NTP) uses UDP port 123 to maintain accurate time synchronization across systems, which is essential for time-sensitive protocols such as Kerberos authentication.

Step-by-Step Solution

1
Identify the required network service based on the symptom of time skew causing Kerberos authentication failures.
The necessary service is Network Time Protocol (NTP), which provides clock synchronization across devices.
Kerberos relies on accurate timestamps (typically within 5 minutes) to prevent replay attacks.
2
Determine the transport protocol and standard port number used by NTP.
NTP operates over UDP on port 123.
UDP is chosen for its minimal protocol overhead and low latency, which are critical for precise timing.

Key Concept

Network Time Protocol (NTP) operates over UDP port 123 to synchronize system clocks across network devices.
Estimated Time:1m 0s
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Topics

Common Ports and Protocols

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