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Difficulty: Very hardNTP Client and Server Operations and Configuration

A network engineer is configuring a new Cisco IOS router (R1) to synchronize its system time with a primary enterprise NTP server operating at Stratum 2. R1 is also expected to act as an NTP server for downstream switches once synchronized. Arrange the operational steps in the exact chronological sequence in which R1 processes NTP synchronization from initial CLI configuration to serving downstream clients.

  1. 1The administrator executes the global configuration command 'ntp server 10.10.10.1' on R1.
  2. 2R1 generates and transmits NTP request packets to IP 10.10.10.1 using UDP destination port 123.
  3. 3R1 receives an NTP response packet from 10.10.10.1 carrying a Stratum level of 2 and server reference timestamp data.
  4. 4R1 validates the reference clock and calculates its own local Stratum level as 3 by adding 1 to the received server stratum.
  5. 5R1 transitions its internal clock state to 'synchronized' and begins answering NTP requests from downstream devices at Stratum 3.

Answer

The correct sequence starts with entering the NTP server configuration command, followed by sending UDP port 123 query packets, receiving the Stratum 2 response, calculating the local Stratum 3 value, and finally transitioning to synchronized state while serving downstream clients.
The operational sequence moves logically from CLI command execution, outward network request over UDP 123, inbound response processing, mathematical stratum calculation (2+1=32 + 1 = 3), to local state synchronization and downstream service activation.

Step-by-Step Solution

1
Identify the initial configuration trigger
Execution of 'ntp server 10.10.10.1' initializes the local NTP daemon polling timer.
NTP operations cannot begin until a server association is defined in configuration.
2
Determine initial packet transmission details
R1 sends outgoing NTP client polling messages using UDP port 123.
NTP uses UDP port 123 for all client/server communications.
3
Process server response details
R1 receives packet payload containing Stratum 2 marker from 10.10.10.1.
The upstream server reports its own stratum distance from reference clock (Stratum 2).
4
Perform Stratum level mathematical calculation
Local stratum is evaluated as Server Stratum+1=2+1=3\text{Server Stratum} + 1 = 2 + 1 = 3.
Every network hop down the NTP hierarchy increments the Stratum level by exactly 1.
5
Establish synchronized state and downstream server role
System clock updates to synchronized state, enabling R1 to answer downstream queries at Stratum 3.
A Cisco router will not serve authoritative time to downstream clients until its own clock is synchronized to an upstream source.

Key Concept

NTP Client-Server Synchronization Workflow and Stratum Calculation
Estimated Time:2m 0s
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Topics

NTP Client and Server Operations and Configuration

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