IntermediatePublished 2026-07-04
Redundant Time Sources with prefer
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CCNA exam domain: IP Services
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
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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.
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