NTP & Network Time

Configure a Cisco IOS router as an authoritative NTP master at a chosen stratum and point a neighbor at it as a client. Understand how NTP stratum works and verify deterministically using show commands rather than waiting for live synchronization.

Configure two Cisco IOS routers as symmetric-active NTP peers over a single /30 link. R1 is an authoritative clock (ntp master 4) and both routers form a symmetric peer relationship with ntp peer. Learn how peer mode differs from client/server, and how to verify and troubleshoot associations without relying on Internet sources.

Configure NTP MD5 authentication so a client (R2) synchronizes only to a trusted, authenticated master (R1). R1 is already an authoritative clock (ntp master 3). You will enable NTP authentication on both routers, define and trust key 1, and bind the key on R2's ntp server statement. Verification focuses on authenticated associations and status; actual time lock may take minutes and is not graded.

Configure a deterministic NTP broadcast design on a single shared LAN. R1 acts as an authoritative clock (ntp master 3) and broadcasts time on its LAN interface. R2 and R3 act as broadcast clients to scale time distribution without per-client server statements. Verify broadcast associations on the clients and understand the tradeoffs vs. unicast client/server.

Configure a Cisco IOS router as an authoritative NTP master and restrict which clients it will serve using an NTP access-group with a standard ACL. One shared LAN (no routing) connects three routers through a Layer-2 switch. Only R2 is authorized to receive time from R1; R3 is denied. Learners deploy, verify, and troubleshoot the access-group behavior.

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.

Create a deterministic three-tier NTP hierarchy on a single shared LAN. R1 is the authoritative clock (ntp master 2), R2 syncs to R1, and R3 syncs to R2. No routing or additional subnets — all devices share 10.0.0.0/24 via one L2 switch. Verify with show ntp status and show ntp associations.

Two-router /30 point-to-point lab. R1 is an authoritative UTC NTP master (stratum 3). Configure R2 as an NTP client to R1 and display local time in MST/MDT while remaining synchronized to UTC. Reinforces that NTP distributes UTC and the router applies timezone/daylight-saving only to presentation.

Advanced NTP capstone, run as a fault hunt. Two branch routers disagree about the time and neither will sync, despite both being configured for NTP and able to ping each other. You get symptoms and the required end state — no fault list. Faults sit on both devices, and two of them make NTP fail while the configuration reads as though it should work — including a restriction pointing at something that was never created.