Setting Router Clocks in Cisco Devices

Nerd Caf

In this lesson, I'll guide you step by step on how to set the clock on a Cisco router. This is an essential task in networking, as an incorrect time setting can impact logging, authentication protocols, and network synchronization.

Step 1: Understand the Importance of Router Clock

Before we start configuring, let's understand why setting the correct time on a router is important:

• Accurate Logging: Ensures that logs have the correct timestamps.

• Security Protocols: Some authentication mechanisms depend on synchronized clocks.

• Network Management: Helps in troubleshooting and performance monitoring.

Cisco routers do not have a built-in battery-backed clock like computers. They lose their time setting when rebooted unless a Network Time Protocol (NTP) server is used.

Step 2: Check the Current Clock Setting

To check the router's current date and time, use:

Router# show clock

Router#show clock
*14:30:33.211 UTC Mon Mar 31 2025
Router#

The asterisk (*) indicates the clock is not set.

Step 3: Manually Set the Clock

You can manually set the clock using the following command:

Router#clock set ?
  hh:mm:ss  Current Time

Router#clock set 18:01:00 ?
  <1-31>  Day of the month
  MONTH   Month of the year

Router#clock set 18:01:00 31 ?
  MONTH  Month of the year

Router#clock set 18:01:00 31 March ?
  <1993-2035>  Year

Router#clock set 18:01:00 31 March 2025
Router#
*Mar 31 18:01:00.000: %SYS-6-CLOCKUPDATE: System clock has been updated from 14:32:20 UTC Mon Mar 31 2025 to 18:01:00 UTC Mon Mar 31 2025, configured from console by console.
Router#

Breakdown of the command:

• 14:30:00 → Time in 24-hour format.

• 31 → Day of the month.

• Mar → Three-letter abbreviation for the month.

• 2025 → Year.

Step 4: Verify the Clock

After setting the clock, verify it using:

Router#show clock
18:02:27.855 UTC Mon Mar 31 2025
Router#

Step 5: Set the Time Zone

By default, the router uses UTC (Coordinated Universal Time). To set your local time zone, use:

Router(config)#clock timezone ?
  WORD  name of time zone

Router(config)#clock timezone IRST ?
  <-23 - 23>  Hours offset from UTC

Router(config)#clock timezone IRST 3 ?
  <0-59>  Minutes offset from UTC
  <cr>

Router(config)#clock timezone IRST 3 30 ?
  <cr>

Router(config)#clock timezone IRST 3 30
Router(config)#
Mar 31 18:05:10.123: %SYS-6-CLOCKUPDATE: System clock has been updated from 18:05:10 UTC Mon Mar 31 2025 to 21:35:10 IRST Mon Mar 31 2025, configured from console by console.
Router(config)#

Step 6: Save the Configuration

Since Cisco routers lose time when rebooted, you need to configure NTP or manually reset the clock after every restart.

To save the configuration:

Router#write memory
Warning: Attempting to overwrite an NVRAM configuration previously written
by a different version of the system image.
Overwrite the previous NVRAM configuration?[confirm]
Building configuration...
[OK]
Router#

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