A local clock is a router’s internally maintained time source. With ntp master, the router can provide NTP service even without an upstream NTP server, using its own clock as the reference. section 2.3.2
Use external NTP servers first because their reference clocks are more accurate. Configure the local clock as a backup when those servers become unavailable, preserving consistent time across network devices. section 2.3.2
Configure and verify a local-clock fallback
R1(config)# ntp master R1(config)# do show ntp associations The output identifies 127.127.1.1 as the .LOCL. time source. Combine this with ntp server for preferred external synchronization and local-clock backup. section 2.3.2
