NTP

NTP (Network Time Protocol) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in current use.

NTP is intended to synchronize all participating computers to within a few milliseconds of UTC. It uses the intersection algorithm, a modified version of Marzullo’s algorithm, to select accurate time servers and is designed to mitigate the effects of variable network latency. NTP can usually maintain time to within tens of milliseconds over the public Internet, and can achieve better than one millisecond accuracy in local area networks under ideal conditions. Asymmetric routes and network congestion can cause errors of 100 ms or more.

The protocol is usually described in terms of a client-server model, but can as easily be used in peer-to-peer relationships where both peers consider the other to be a potential time source. Implementations send and receive timestamps using UDP on port number 123.

NTP supplies a warning of any impending leap second adjustment, but no information about local time zones or daylight saving time is transmitted.

The current protocol is version 4 (NTPv4), which is a proposed standard as documented in RFC 5905. It is backward compatible with version 3, specified in RFC 1305.

Configuration

set system ntp server <address>

Configure one or more servers for synchronisation. Server name can be either an IP address or FQDN.

There are 3 default NTP server set. You are able to change them.

  • 0.pool.ntp.org
  • 1.pool.ntp.org
  • 2.pool.ntp.org
set system ntp listen-address <address>
Setup VyOS as an NTP responder, you must specify the <address> and optionally the permitted clients. Multiple listen addresses can be configured.
set system ntp allow-clients address <address>
List of networks or client addresses permitted to contact this NTP server. Multiple networks can be configured.