RuggedCom RX1000, RX1100 manual Configuring NTP, NTP Fundamentals

RuggedRouter™ User Guide

Chapter 22 – Configuring NTP

Introduction

This chapter familiarizes the user with:

∙Enabling/Disabling NTP

∙Setting servers and peers

∙Setting generic NTP options

∙NTP Tools

NTP Fundamentals

NTP (Network Time Protocol) is an Internet protocol used to synchronize the clocks of computers to some time reference. Variants of NTP such as SNTP (Simple NTP, a reduced functionality NTP) and XNTP (Experimental NTP) exist. NTP itself is available in versions 3 and 4 (the RuggedRouter includes version 4).

NTP is a fault-tolerant protocol that allows an NTP daemon program to automatically select the best of several available time sources, or reference clocks, to synchronize to. Multiple candidates can be combined to minimize the accumulated error. Temporarily or permanently wrong time sources are detected and avoided.

The NTP daemon achieves synchronization by making small and frequent changes to the router hardware clock.

The NTP daemon operates in a client-server mode, both synchronizing from servers and providing synchronization to peers.

If NTP has a number of servers to choose from, it will synchronize with the lowest stratum server. The stratum is a measure of the number of servers to the (most highly accurate) reference clock. A reference clock itself appears at stratum 0. A server synchronized to a stratum n server will be running at stratum n + 1.

You will generally configure lower stratum NTP hosts as servers and other NTP hosts at the same stratum as peers. If all your configured servers fail, a configured peer will help in providing the NTP time. It is generally a good idea to configure one at least one server and peer.

The NTP daemon will know about the NTP servers and peers to use in three ways.

∙It can be configured manually with a list of servers to poll from,

∙It can be configured manually with a list of peers to send to,

∙It can look at advertisements issued by other servers on multicast or broadcast addresses.

Note that if multicasting or broadcasting is used, it is strongly recommended to enable authentication unless you trust all hosts on the network.

NTP uses UDP/IP packets for data transfer because of the fast connection setup and response times UDP offers. The NTP protocol uses port UDP port 123. Note that if your router employs a firewall and acts as a client it must open UDP port 123.

Additionally, if the router acts as a server the firewall must allow connection requests on port 123 as well.

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