Lab Objective
Manually set the clock on one router and configure it as an NTP server, configure a second router as an NTP client pointing to the first, and verify the client's clock synchronizes to match the server.
Lab Purpose
Accurate, synchronized time across every network device is essential for correlating log timestamps during troubleshooting and for certain security features like certificate validation. NTP is the standard protocol that keeps every device's clock aligned automatically rather than relying on manual clock-setting on each device individually.
Lab Topology
R1 (NTP server) ---- Serial0/0/0 ------ Serial0/0/0 ---- R2 (NTP client)
R1: 10.15.15.1/30
R2: 10.15.15.2/30Task 1: Manually Set R1's Clock
Set R1's clock to a specific known date and time.
Task 2: Configure R1 as an NTP Master
Configure R1 to act as an authoritative NTP time source.
Task 3: Verify R2's Clock Is Different Before Syncing
Check R2's current clock and confirm it does not match R1's, since no synchronization has occurred yet.
Task 4: Configure R2 as an NTP Client
Point R2 to R1 as its NTP time source.
Task 5: Verify Synchronization
Confirm R2's clock converges to match R1's, and check the NTP association status.
Solution and Verification
R1# clock set 14:00:00 15 June 2026R1(config)# ntp master 3
-- The "3" sets R1's stratum level -- stratum
-- indicates distance from an authoritative
-- reference clock, with lower numbers being
-- more authoritative; "ntp master" makes R1
-- itself the authoritative source for this labR2# show clock
*10:42:18.123 UTC Mon Jan 12 2026
-- R2's clock is completely different from
-- R1's manually set time, confirming no
-- synchronization has occurred yetR2(config)# ntp server 10.15.15.1R2# show ntp associations
address ref clock st when poll reach delay offset
*~10.15.15.1 127.127.1.1 3 12 64 17 4.2 0.891
-- The asterisk (*) indicates R2 has selected
-- this as its synchronized time source
R2# show clock
14:03:22.456 UTC Mon Jun 15 2026
-- R2's clock now matches R1's, confirmed
-- synchronized rather than in a free-running
-- state (shown without the leading asterisk
-- that indicates an unsynchronized clock)Key Takeaway
The asterisk in show ntp associations output is the definitive confirmation that synchronization has actually succeeded — a configured NTP server with no asterisk next to it means the client has not yet synced with that source, which is the first thing to check when device clocks remain mismatched despite NTP appearing to be configured correctly.