ntp master [stratum]
Configures the router to act as an NTP master server, providing time synchronization to other devices when no external NTP source is available.
ntp master [stratum]When to Use This Command
- Setting up a small lab or isolated network where no external NTP server is reachable, using the router as the time source.
- Configuring a router as a backup NTP server for a branch office that loses WAN connectivity to the primary NTP server.
- Providing a local NTP source for network devices in a secure environment where external NTP access is blocked.
- Using a router as the NTP master for a network segment to reduce load on external servers and improve time accuracy.
Command Examples
Basic NTP Master with Default Stratum
ntp masterNo output is generated. The command configures the router as an NTP master with default stratum 8. The router will serve time to NTP clients.
NTP Master with Custom Stratum
ntp master 5No output is generated. The command sets the router's NTP stratum to 5, making it appear closer to the authoritative time source (lower stratum is better). Clients will prefer lower stratum servers.
Understanding the Output
The 'ntp master' command does not produce any output upon execution. To verify the configuration, use 'show ntp status' or 'show ntp associations'. In 'show ntp status', look for 'Clock is synchronized' and the stratum level. A lower stratum (e.g., 5) indicates higher accuracy. If the router is not synchronized to any external source, it will serve time at its configured stratum. Ensure that the NTP master is reachable by clients and that NTP is enabled globally with 'ntp enable' if required.
CCNA Exam Tips
Remember that 'ntp master' sets the router as an NTP server; the default stratum is 8, but you can set it from 1 to 15.
In the CCNA exam, know that a lower stratum number means higher priority; a stratum 1 device is directly connected to an authoritative time source.
Be aware that 'ntp master' is used when there is no external NTP source; if an external source is available, use 'ntp server' instead.
The 'show ntp status' command displays the current stratum and synchronization status; a stratum of 16 means unsynchronized.
Common Mistakes
Forgetting to enable NTP globally with 'ntp enable' on some platforms, causing the master to not respond to clients.
Setting the stratum too low (e.g., 1) without an actual reference clock, misleading clients about time accuracy.
Using 'ntp master' on a router that is also configured as an NTP client with 'ntp server', which can cause conflicts.
Related Commands
ntp server [ip]
Configures the router to synchronize its system clock with an NTP server, ensuring accurate time for logging, authentication, and network protocols.
show ntp associations
Displays the status of NTP associations configured on the device, used to verify NTP synchronization and identify time sources.
show ntp status
Displays the current NTP synchronization status, including clock stratum, reference clock, and synchronization state, used to verify NTP operation and clock accuracy.
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