RE: NTP Server

[Brandon Kim <brandon.kim () brandontek com>]

Hi Sean:

By local I meant in-house, on-site in our datacenter. As far as what applications could use our NTP service, I would
leave that up to each client and what they are running. For my own personal purposes, it would just be for log 
purposes. 
(error logs, syslogs, etc etc)

I have heard that routers don't make good NTP servers since they weren't designed to keep track of time. This, I have 
read
from a Cisco source. Can't remember where though. Or maybe they were just referring to older less powerful routers like 
2500 series...

Brandon






> Date: Sun, 24 Oct 2010 14:42:24 -0400
> From: sean () donelan com
> To: nanog () nanog org
> Subject: Re: NTP Server
>
> On Sun, 24 Oct 2010, Brandon Kim wrote:
> > 1) How necessary do you believe in local NTP servers? Do you really 
> > need the logs to be perfectly accurate?
> > 2) If you do have a local NTP server, is it only for local internal 
> > use, or do you provide this NTP server to your clients as an added 
> > service?
> > 3) If you do have a local NTP server, do you have a standby local NTP 
> > server or do you use the internet as your standby server?
>
> First terminology.  What do you mean by a local NTP server?
>
> Almost any Cisco/Juniper router, Unix server and some recent Windows 
> servers have NTP server software and can synchronize clocks in your 
> network.  So you may already have a NTP server capable device.  You just 
> need to configure it, and give it a good source of time.  It would be a 
> Stratum 2 or greater NTP server because the good source of time is 
> another NTP server.  Left to itself, NTP is pretty good at keeping clocks 
> in arbitrary networks synchronized with each other. But most people are 
> also interested in synchronizing clocks with some official time source.
>
> The Network Time Protocol doesn't really have the notion of a "standby" 
> server.  It uses multiple time sources together, and works best with about 
> four time sources.  But for many end-systems, the Simple Network Time 
> Protocol with a single time source may be sufficient.
>
> If you are in a regulated industry (stock broker, electric utility, 9-1-1 
> answering point, etc) there are specific time and frequency standards you 
> must follow.
>
> On the other hand, are you are asking about a local clock receiver (radio, 
> satellite, etc) for a stratum 1 NTP server?  Clock receivers are getting 
> cheaper, the problem is usually the antenna location.
>
> Or on the third hand, are you asking about local primary reference clock 
> (caesium, rubium, etc) for a stratum 1 NTP server?  These are still 
> relatively expensive up to extremely expensive.
>
> Or on the fourth hand, are you a time scientist working to improve 
> international time standards.  If you are one of these folks, you already
> know.
>
>
> Most major ISPs use NTP across their router backbone, and incidently 
> provide it to their customers. The local ISP router connected to your 
> circuit probably has NTP enabled.
>
> Required accuracy is in the eye of the beholder. NASDAQ requires brokers 
> to have their clocks synchronized within 3 seconds of UTC(NIST).  9-1-1 
> centers are required to have their clocks synchronized within 0.5 seconds 
> of UTC.  Kerberos/Active Directory requires clocks to be synchronized 
> within 5 minutes of each other.
>
> If your log files have a resolution of 1 second, you probably won't see 
> much benefit of sub-second clock precision or accuracy.  If you are 
> conducting distributed measurements with sub-microsecond resolution, you
> probably will want something more.