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Difficulty: MediumNTP Client and Server Operations and Configuration

A network administrator is configuring time synchronization on a newly installed Cisco IOS router. Arrange the following operational events in the correct chronological order, from initial CLI configuration to serving downstream clients.

  1. 1The administrator configures the global command `ntp server 10.1.1.50` to establish an association with an upstream Stratum 2 server.
  2. 2The local router exchanges NTP poll packets with 10.1.1.50 to measure network latency, dispersion, and time offset.
  3. 3The router updates its local system clock using the offset calculated from the server response data.
  4. 4The router updates its internal operational state to synchronized and sets its local stratum to Stratum 3.
  5. 5The router answers incoming time requests from downstream LAN switches as an authoritative NTP server.

Answer

The correct operational sequence is: 1) Executing `ntp server 10.1.1.50` on the router, 2) Exchanging NTP polling messages to calculate delay and offset, 3) Adjusting the local system clock, 4) Transitioning to a synchronized state at Stratum 3 (upstream + 1), and 5) Responding to downstream client requests at Stratum 3.
The NTP operation sequence begins with establishing the peer/server relationship via `ntp server`. Polling packets are then exchanged to calculate offset and dispersion. Once metrics are validated, the local clock synchronizes, allowing the router to assign itself Stratum 3 (upstream Stratum 2 + 1). Finally, the router serves downstream clients accurately.

Step-by-Step Solution

1
Identify the initial configuration trigger
The command `ntp server 10.1.1.50` creates the server association.
No NTP message exchange can take place until the target IP server is defined in the configuration.
2
Analyze the packet exchange sequence
The router initiates NTP polling requests over UDP port 123.
Timestamped control packets must be exchanged to filter dispersion and compute clock offset.
3
Determine system clock adjustment
The system clock synchronizes to the upstream reference time.
Clock offset calculation must be completed before the router can adjust its internal clock.
4
Calculate the local stratum level
Stratum level becomes Stratum 2 + 1 = Stratum 3.
NTP protocol rules state that a device takes on the stratum level of its reference server plus one.
5
Identify downstream server operation
The router acts as an authoritative time source for internal network devices.
A Cisco router only advertises valid, authoritative time to clients after its own clock is synchronized.

Key Concept

NTP Synchronization Sequence and Stratum Propagation
Estimated Time:1m 30s
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Topics

NTP Client and Server Operations and Configuration

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