NTP era 0 rollover

NTP packets up to version 4 carry an unsigned 32-bit seconds field counted from 1 January 1900. That field wraps at 2036-02-07 06:28:16 UTC. The protocol has an era number; older packets do not transmit it. Clients must infer the era from an approximate local clock. A 32-bit Unix host that later jumps to 1901 in 2038 is more than 68 years off and can lose NTP lock.

This is a wire-format deadline. A 64-bit operating system still speaks 32-bit NTP seconds on the network.

Primary explainers: Mills’ NTP “Year 2036” notes; Meinberg “Time Synchronization and Rollovers”.