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NTP Overview

The Network Time Protocol (NTP) provides the mechanisms to synchronize time and coordinate time distribution in a large, diverse network. NTP uses a returnable-time design in which a distributed subnet of time servers operating in a self-organizing, hierarchical primary-secondary configuration synchronizes local clocks within the subnet and to national time standards by means of wire or radio. The servers also can redistribute reference time using local routing algorithms and time daemons.

NTP is defined in RFC 1305, Network Time Protocol (Version 3) Specification, Implementation and Analysis.

For Common Criteria compliance, configure NTP to provide accurate timestamps for system log messages.

Note: NTP does not support VPN routing and forwarding (VRF) requests. The router cannot process these requests properly because NTP uses the inet.0 route table for route resolution to the requestor and thus cannot propagate routes using the routing-instance-name.inet.0 VRF table for the VPN.

When configuring NTP, you do not actively configure time servers. Rather, all clients also are servers. An NTP server is not believed unless it, in turn, is synchronized to another NTP server—which itself must be synchronized to something upstream, eventually terminating in a high-precision clock.

By default, if the time difference between the local router clock and the NTP server clock is more than 128 milliseconds, the clocks are slowly stepped into synchronization. However, if the difference is more than 1000 seconds, the clocks are not synchronized. On the local router, you set the date and time using the set date command. To set the time automatically, use the boot-server statement at the [edit system ntp] hierarchy level, specifying the address of an NTP server.

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