RuggedCom RuggedRouter RX1100 - Manual (Page 256)

29. Configuring NTP
Revision 1.14.3 256 RX1000/RX1100™
29. Configuring NTP
29.1. Introduction
This chapter familiarizes the user with:
• Enabling/Disabling NTP
• Setting servers and peers
• Setting generic NTP options
• NTP Tools
29.1.1. 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 (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,
• 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.