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Difficulty: HardNTP Client and Server Operations and Configuration

An administrator inspects the output of the `show ntp associations` command on router Core-R1:

text
address ref clock st when poll reach delay offset disp
*~192.168.50.2 10.1.1.1 2 15 64 377 2.12 0.18 0.45
~192.168.60.2 127.127.1.1 16 - 64 0 0.00 0.00 16000.

Core-R1 is also configured with the `ntp master 6` command. Router Branch-R2 is configured to synchronize its clock with Core-R1 using the command `ntp server 192.168.10.1` (Core-R1's IP address).

Which statement accurately describes the resulting NTP operational status and stratum hierarchy for both devices once synchronization is fully established?

  1. Core-R1 operates at Stratum 3, and Branch-R2 operates at Stratum 4.Answer
  2. B
    Core-R1 operates at Stratum 6, and Branch-R2 operates at Stratum 7.
  3. C
    Core-R1 operates at Stratum 2, and Branch-R2 operates at Stratum 3.
  4. D
    Core-R1 operates at Stratum 16, preventing Branch-R2 from synchronizing.

Answer

Core-R1 operates at Stratum 3, and Branch-R2 operates at Stratum 4.
In Cisco IOS NTP operation, an asterisk (`*`) in `show ntp associations` designates the current synchronized time source. Because 192.168.50.2 is at Stratum 2, Core-R1 becomes Stratum 3 (2+1=32 + 1 = 3). The `ntp master` command acts only as an authoritative clock fallback when no synchronized upstream clock is present, so `ntp master 6` is inactive. Consequently, Branch-R2 synchronizing to Core-R1 receives Stratum 3 time and becomes Stratum 4 (3+1=43 + 1 = 4).

Step-by-Step Solution

1
Analyze the output of `show ntp associations` on Core-R1.
The asterisk `*` next to `192.168.50.2` indicates that Core-R1 is actively synchronized to this server. The `st` column shows that this server operates at Stratum 2.
An NTP client increments the stratum value of its configured reference clock by 11.
2
Evaluate the impact of the `ntp master 6` command on Core-R1.
Core-R1's effective stratum is 2+1=32 + 1 = 3. The `ntp master 6` setting is ignored.
The `ntp master` command serves as a fallback clock source only when no active, valid external NTP server is synchronized.
3
Calculate the stratum level for Branch-R2.
Branch-R2 synchronizes to Core-R1 (Stratum 3), resulting in a stratum level of 3+1=43 + 1 = 4 for Branch-R2.
Each hop down the NTP distribution tree adds 11 to the stratum level.

Key Concept

NTP Stratum Hierarchy and Precedence
Estimated Time:2m 0s
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Topics

NTP Client and Server Operations and Configuration

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