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Difficulty: MediumNTP Client and Server Operations and Configuration

A network router is configured with the global configuration command `ntp master 6`. Additionally, the router has a configured association using `ntp server 172.16.40.10`. The remote NTP server at IP address 172.16.40.10172.16.40.10 is reachable and currently operates at Stratum 3. Assuming time synchronization between the router and the remote server succeeds, what stratum level will this router advertise to its downstream NTP clients?

  1. A
    Stratum 3
  2. Stratum 4Answer
  3. C
    Stratum 6
  4. D
    Stratum 16

Answer

The router will operate at and advertise Stratum 4 because it adds 1 to the stratum level of its active upstream reference source (Stratum 3).
In Network Time Protocol (NTP), stratum levels represent the distance from an authoritative reference clock (Stratum 0). When a router synchronizes with an NTP server at Stratum NN, the router's calculated stratum level becomes N+1N + 1. Since the upstream server is at Stratum 3, the router synchronizes to it and operates at Stratum 4. The `ntp master [stratum]` command configures the router as a master NTP server using its own internal clock only if external NTP sources fail or are unreachable.

Step-by-Step Solution

1
Determine the active NTP source
The router has an active, reachable NTP server at 172.16.40.10 operating at Stratum 3.
An active external NTP server association takes precedence over the internal `ntp master` fallback command.
2
Calculate the local router's stratum level
Stratum level = Upstream Stratum + 1 = 3 + 1 = 4.
NTP stratum levels increment by 1 for each hop away from the authoritative reference clock (Stratum 0).

Key Concept

NTP Stratum Calculation and Fallback Master Precedence
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Topics

NTP Client and Server Operations and Configuration

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