Home Bundles NTP & Network Time Redundant Time Sources with prefer Intermediate Published 2026-07-04
Redundant Time Sources with prefer Bundle lab · $29.99
Build a small LAN with two IOS routers acting as NTP masters at different strata and a client that lists both as time sources, preferring one using the prefer keyword. All routers share a single broadcast domain via a Layer-2 switch, with no routing configured. You will deploy deterministic NTP, verify associations, and understand redundancy selection behavior.
Learning objectives Configure two IOS routers as authoritative NTP masters at different strata Configure a client router to use multiple NTP servers and prefer one source Verify NTP associations and system peer selection with show commands Explain how prefer biases selection when multiple usable sources exist Troubleshooting focus Wrong or missing ntp master on a server prevents client selection Incorrect server IP or interface down on the client Prefer keyword on the non-existent or unreachable server has no effect Clock sync requires time; do not misinterpret transient output What's included in the package Work / baseline CML import — lab-work.yaml Topology diagram — topology.svg Print-ready topology diagram (PDF) — topology.pdf Step-by-step learner guide (Markdown — for Obsidian/VS Code) — lab-guide.md Branded PDF lab guide — open in any viewer (Adobe/Preview) — lab-guide.pdf Getting-started README — README.md Verification checklist — verification-checklist.md How this lab is graded Build it your way. Where a lab lets you choose a value — a VLAN name, an interface description — grading checks that you configured it, not which name you picked. Names that another line has to reference, like an ACL applied with access-class, are stated in the guide and do have to match.Addresses, modes and protocol keywords are exact. An IP address, a subnet mask, switchport mode trunk, an encapsulation — these carry the meaning of the lab, so they are graded as written in the guide.Grading reads your saved configuration. Export the lab from CML after you have configured it, and make sure anything you set is in the running-config — a change that only exists in a terminal session never reaches the grader.You can submit as many times as you like. Your best score stands, and each attempt tells you which checks passed so you can work the gaps.Scored something you believe is correct? Use Report an issue on this page — that is exactly how the grading fixes in the changelog got found. Download access New here? See how the download → build in CML → grade loop works.
This lab is part of the NTP & Network Time bundle — own every lab in it permanently for a one-time $29.99.
Create a free account, then own the NTP & Network Time bundle for a one-time $29.99 — buy once, keep every lab forever.
Found a problem with this lab? Please sign in to report a problem — tying it to your attempts lets us reproduce and fix it faster.
