Network Time Protocol (NTP)

What is NTP Stratum?

Stratum is a term that means different things depending on the context.  In the world of NTP, stratum is defined in RFC 1305.  NTP uses a hierarchical structure in which Stratum 0 is the reference clock, linked via a time signal, to a reliable source of UTC.  Stratum 1 is the time server with a direct link to the reference clock.  Stratum 2 is a client that receives time over a network connection from a Stratum 1 clock.  Stratum 3 is a client that receives time from a Stratum 2 clock.  And so on, up to Stratum 15.  For more details on strata in the NTP world, click here.


How accurate is NTP?

Over WANs (Wide Area Networks), up to 100 milliseconds is typical.  It depends on how far away the public time server is, or more specifically, how many hops between you and the server.  Within a LAN (Local Area Network) using a dedicated NTP Time Server, 0.5 to 2 milliseconds is typical.  The internal accuracy of the CDMA Network Time Server is on the order of 10 microseconds.  It can easily keep all clients on a LAN synchronized to typically within 0.5 to 2 milliseconds.


Where can I get NTP client software?

Client software is widely available as freeware and shareware.  Setting up an NTP or SNTP client is relatively simple once you have installed the software on your workstation and communicated with the time server over the network.  For a list of NTP client software click here.


How long will the NTP Server deliver Stratum 1 performance if the signal is lost?

Exclusive EndRun oscillator-control algorithms provide extended Stratum 1 holdover performance when the unit is not locked to the synchronization signal (GPS or CDMA).  Typical NTP Stratum 1 holdover periods are:
    24 hours - TCXO (standard)
    35 days - OCXO (upgrade)
    140 days - Rubidium (upgrade)


Why do I need a time server?

When two or more computers are involved, accurate time keeping is difficult, especially if they are not in the same physical location.  A dedicated time server inside your network perimeter is the most accurate, reliable and secure way to ensure accurate timekeeping for all computers on your network.  Accurate timekeeping is necessary to support eBusiness and other applications such as Stock Trades, Logs, B2B Transactions, File Operations, Packet Time Stamps, Software Configuration Management, Database Accuracy, Telecommunication Call Billing, etc.  For a more detailed response to this question click here.


Why not use the time servers available over the Internet?

There are many public time servers available over the Internet.  Access to these public time servers is free of charge.  While public time servers are certainly less costly - accurate, reliable and secure time is best provided by a dedicated time server that resides under your control inside your network security perimeter.  Using public time servers available over the Internet is not recommended for the following reasons:

1.  Setting up your firewall to accept NTP packets (which is based on UDP/IP) introduces a security risk that many Network Administrators are not willing to take.

2.  Time accuracy degrades because of indeterminate network latency, up to 100 milliseconds is typical.


Is there a command to tell me the Stratum level of my NTP Server?

Yes.  For current models (Sonoma, Meridian II, Tycho II, RTM3205) use Linux command:

   ntpq -c sysinfo

For legacy models use Linux command:

   ntpdc -c sysinfo


How many clients can a time server handle?

For a detailed answer to this question click here.

Is support for NTS4NTP on your product roadmap?

Yes.  NTS4NTP is in the draft standard level and when released we expect it will be integrated into the NTP distribution.  The Time Servers are periodically upgraded with the latest distribution so when NTS4NTP is supported, then it will also be supported in our products.  The standards process is lengthy so there is no telling when this capability will be in the NTP distribution.

Are the EndRun NTP Servers compliant with STIG ID: NET0813, Rule ID: SV-15326r5?

EndRun NTP Servers are compliant with STIG ID: NET0813,  Rule ID: SV-15326r5,  Vuln ID:  V-14671.  The time servers support a FIPS-approved message authentication code and NIST-approved HMAC algorithms.

How do I restart the NTP daemon without rebooting?

For our third generation units such as Sonoma, Meridian II, Tycho II, Ninja, RTM3205 and e-Series Distribution, run the command:

   /etc/rc.d/rc.ntpd restart

For older models, the only way to restart the daemon is to reboot.