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NTP — one trusted clock for the whole network
Enterprise Beginner 3 devices 3 checked tasks 100 points Free lab
Logs from devices with different clocks cannot be lined up, certificates fail, and Kerberos breaks. Make one router the authoritative time source (stratum 3) and the others synchronise to it, then check the association shows as synchronised, not just configured. You build it in a browser, type real commands at each device, and every task below is
checked against the running configuration — so you find out it is wrong before anybody else does.
Open this lab in the simulator
The simulator runs in your browser with nothing to install. This is a free lab: it stays open on the free plan. It needs an account, which keeps your progress.
The scenario
Logs from devices with different clocks cannot be lined up, certificates fail, and Kerberos breaks. Make one router the authoritative time source (stratum 3) and the others synchronise to it, then check the association shows as synchronised, not just configured.
Your role: a network engineer on the enterprise team. Level: Beginner Done when: all 3 goals show as passed (100 points).
Network status
Devices: 3 routers, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. R-Master starts with addresses (G0/0 10.0.1.1/30, G0/1 10.0.2.1/30). R-A starts with addresses (G0/0 10.0.1.2/30). R-B starts with addresses (G0/0 10.0.2.2/30). Known problems
The network worked and now does not: the scenario above says what users report. The cause is a configuration fault, not a cable. Find it with show commands (interfaces, routes, neighbours, running-config) before you change anything; fix only what is wrong. Goals
R-Master is the authoritative time source (30 pts) R-A synchronises to R-Master (35 pts) R-B synchronises to R-Master (35 pts) The activity, in order
R-Master is the authoritative time source Why: This is the task that checks your configuration directly: the line must really be there, not just look right. Verify with: show running-config R-A synchronises to R-Master Why: Each goal is a state the lab can check on the running device. Verify with: show running-config R-B synchronises to R-Master Why: Each goal is a state the lab can check on the running device. Verify with: show running-config Tips
Work in the order given: later goals depend on the earlier ones. After every change, run the verify command before moving on; do not guess. Stuck? Read the verify output first. It names the interface, neighbour or route that is wrong. Common mistake: Expecting instant synchronisation Common mistake: No route to the NTP server Common mistake: Setting the clock by hand on a client and wondering why it drifts Why this matters
Logs from devices with different clocks cannot be correlated and certificate validation fails. NTP builds a hierarchy of strata from a trusted source.
What you will be able to do
Make one device an authoritative source
Synchronise clients to it
Distinguish “configured” from “synchronised”
The network
ISR 2911 — 3 devices in all, already cabled.
Gi0/0 10.0.1.1/30 Gi0/0 10.0.1.2/30 Gi0/1 10.0.2.1/30 Gi0/0 10.0.2.2/30 R-Master R-A R-B Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
R-Master ISR 2911 configure it R-A ISR 2911 configure it R-B ISR 2911 configure it
Cabling
R-Master Gi0/0 ↔ R-A Gi0/0 R-Master Gi0/1 ↔ R-B Gi0/0
What is configured at the start
These are already configured when the lab opens — including, where this is a troubleshooting lab, the fault itself:
R-Master interface g0/0
ip address 10.0.1.1 255.255.255.252
no shutdown
exit
interface g0/1
ip address 10.0.2.1 255.255.255.252
no shutdown
exit R-A interface g0/0
ip address 10.0.1.2 255.255.255.252
no shutdown
exit R-B interface g0/0
ip address 10.0.2.2 255.255.255.252
no shutdown
exit Tasks, and how each one is checked
Every task is decided by reading the live network — a neighbour in FULL, a ping that succeeds, a line in the running configuration — not by looking for a keyword you typed. The same command shows you what the lab sees.
# Task Pts How to verify it yourself
1 R-Master is the authoritative time source 30 On R-Master: show running-config contains the line(s) matching ntp master. 2 R-A synchronises to R-Master 35 On R-A: show ntp status says synchronized. 3 R-B synchronises to R-Master 35 On R-B: show ntp status says synchronized.
Stuck? Ask the coach
Tell the coach what you see or what you tried. It gives you a hint, not the answer, the way a senior engineer would. Included with a free trial or any plan.
Ask the coach
Common mistakes
Expecting instant synchronisation
No route to the NTP server
Setting the clock by hand on a client and wondering why it drifts
Reference solution
Try it yourself first — the lab checks your work either way. This is one configuration that makes every task pass, device by device:
R-Master ntp master 3 R-A ntp server 10.0.1.1 R-B ntp server 10.0.2.1 Where this is examined
CCNA (IP services), Network+ (NTP), Security+ (logging).
This lab practises these topics in the zNetLaB certification courses:
Related labs
Where to start
The lessons all guided labs plans
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