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Difficulty: MediumNTP Client and Server Operations and Configuration

An administrator executes the `show ntp associations` command on a Cisco IOS router to verify system time synchronization. The command output is displayed below:

text
address ref clock st when poll reach delay offset disp
~172.16.50.2 10.1.1.1 2 42 64 377 12.45 1.120 0.45
*192.168.20.5 10.1.1.1 2 15 64 377 4.10 0.210 0.15

Based on this output, which statement accurately describes the NTP operational status of the local router?

  1. The router is synchronized to 192.168.20.5 and will operate as a Stratum 3 NTP server for downstream clients.Answer
  2. B
    The router is synchronized to 172.16.50.2 because the tilde (~) prefix signifies the active master reference source.
  3. C
    The router is synchronized to 192.168.20.5 and will operate as a Stratum 2 NTP server for downstream clients.
  4. D
    The router is unsynchronized because both configured upstream servers report identical reference clock IP addresses.

Answer

The router is synchronized to 192.168.20.5 and will operate as a Stratum 3 NTP server for downstream clients.
In Cisco IOS `show ntp associations` output, the asterisk (`*`) denotes the server with which the router is currently synchronized. Since the server at 192.168.20.5 has a stratum level of 2 (`st = 2`), the local router increments this value by 1, operating as a Stratum 3 NTP server when serving downstream clients.

Step-by-Step Solution

1
Analyze the symbol prefix in the `show ntp associations` output.
The asterisk (`*`) symbol next to `192.168.20.5` indicates that this IP address is selected as the current synchronized reference clock. The tilde (`~`) symbol indicates a configured association.
Cisco IOS uses symbol codes in CLI outputs to distinguish between candidate peers, configured servers, and the actively chosen time source.
2
Determine the stratum level of the upstream time server.
The `st` column for `192.168.20.5` displays a stratum value of 2.
Stratum measures the distance from a high-precision reference clock (Stratum 0).
3
Calculate the stratum level of the local router.
Local Stratum = Upstream Stratum + 1 = 2 + 1 = 3.
An NTP client/server increments the stratum number by 1 relative to its synchronized server.

Key Concept

NTP Output Verification and Stratum Hierarchy Calculation
Estimated Time:1m 15s
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Topics

NTP Client and Server Operations and Configuration

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