Network Time Protocol

The Network Time Protocol (NTP) service on TNSR synchronizes the host clock with reference sources, typically remote servers. It also acts as an NTP server for clients.

NTP Service Example

Configure the NTP Service from configuration mode (Configuration Mode). This example uses pool.ntp.org in pool mode so that multiple DNS results are used as reference servers.

tnsr(config)# ntp server
tnsr(config-ntp)# tos orphan 12
tnsr(config-ntp)# tinker panic 0
tnsr(config-ntp)# logconfig sequence 1 set sync all
tnsr(config-ntp)# logconfig sequence 2 add clock all
tnsr(config-ntp)# restrict default
tnsr(config-ntp-restrict)# kod
tnsr(config-ntp-restrict)# limited
tnsr(config-ntp-restrict)# nomodify
tnsr(config-ntp-restrict)# nopeer
tnsr(config-ntp-restrict)# notrap
tnsr(config-ntp-restrict)# exit
tnsr(config-ntp)# restrict source
tnsr(config-ntp-restrict)# kod
tnsr(config-ntp-restrict)# limited
tnsr(config-ntp-restrict)# nomodify
tnsr(config-ntp-restrict)# notrap
tnsr(config-ntp-restrict)# exit
tnsr(config-ntp)# server host pool.ntp.org
tnsr(config-ntp-server)# operational-mode pool
tnsr(config-ntp-server)# maxpoll 9
tnsr(config-ntp-server)# exit
tnsr(config-ntp)# exit
tnsr(config)# ntp enable
tnsr(config)#

NTP Best Practices

Use a minimum of three servers, either as three separate server entries or a pool containing three or more servers. This is to ensure that if the clock on any one server becomes skewed, the remaining two sources can be used to determine that the skewed server is no longer viable. Otherwise NTP would have to guess which one is accurate and which is skewed.

There are a large number of public NTP servers available under pool.ntp.org. The pool.ntp.org DNS entry will return a number of randomized servers in each DNS query response. These can be used individually or as pools. The easiest way is to use the pool operational mode, which uses all returned servers as if they were specified individually.

When using entries as individual server entries, these responses can be subdivided into mutually exclusive pools of peers to avoid overlap. For example, if a configuration specifies pool.ntp.org multiple times for server entries, the same IP address could accidentally be selected twice. In this case, use 0.pool.ntp.org, 1.pool.ntp.org, 2.pool.ntp.org, and so on. When queried in this way, the responses will be unique for each number.

Furthermore, there are also pools available for regional and other divisions. For example, to only receive responses for servers in the United States, use us.pool.ntp.org as a pool or <n>.us.pool.ntp.org as servers. For more information, see https://www.ntppool.org/en/