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Question

Difficulty: MediumNetworking Ports and Protocols

A systems administrator is troubleshooting an issue where domain-joined workstations in a newly created security zone fail to authenticate against the primary domain controller. Further investigation indicates that the clock on the workstation has drifted significantly from the server time, preventing Kerberos authentication ticket generation. Which port and transport layer protocol combination must be permitted through the internal firewall to restore automatic system clock synchronization across the subnet?

  1. UDP 123Answer
  2. B
    TCP 123
  3. C
    UDP 53
  4. D
    TCP 389

Answer

UDP port 123 is used by the Network Time Protocol (NTP) to synchronize system clocks.
Network Time Protocol (NTP) operates on UDP port 123. It ensures all computers on a network maintain synchronized internal clocks, which is a critical requirement for time-sensitive security protocols such as Kerberos authentication.

Step-by-Step Solution

1
Identify the service requested in the scenario.
The issue involves system clock synchronization to resolve Kerberos authentication failures.
Kerberos authentication relies on tight time synchronization (typically within 5 minutes) between client systems and the domain controller.
2
Determine the protocol and port responsible for time synchronization.
Network Time Protocol (NTP) handles time synchronization on UDP port 123.
NTP is defined to use User Datagram Protocol (UDP) on port 123 for low-latency time updates.

Key Concept

Network Time Protocol (NTP) Port and Transport Protocol
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Topics

Networking Ports and Protocols

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