[131428] in North American Network Operators' Group
Re: NTP Server
daemon@ATHENA.MIT.EDU (Cutler James R)
Sun Oct 24 13:13:00 2010
From: Cutler James R <james.cutler@consultant.com>
In-Reply-To: <SNT119-W52318F85FDEED78E802989DC400@phx.gbl>
Date: Sun, 24 Oct 2010 13:12:40 -0400
To: nanog group <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
Time Service is more complicated than just having a single NTP server. =
But it can be useful and is not really a luxury.
Two primary reasons for local time service are to reliably serve a =
network that is relatively or completely isolated from the general =
internet, and, to provide a local time source for "dumb" clients that is =
closer (less jitter) in network terms. Other reasons can include policy =
(everything in the network uses the same identical time service), policy =
(the time service is locally controlled), operational simplicity (the =
routers don't need to run NTP), and, separation of functions/operational =
responsibility (your run your servers, they run the backbone, I tell you =
the time.
Implementing a local time service is actually fairly simple, but fewer =
than four servers is wasted effort. I can't explain in just a few words =
how the servers interact and compute delays and jitter to come to an =
"accurate" time. Take my word or ask David Mills for all that. =20
Implementation of an internet-referenced time service involves the =
following:
1. Select a set of stratum one servers - pick open access servers or get =
permission to use limited access servers. Four to six should do.
2. Select a set local hosts on your network - DNS servers, for example. =
These should be well distributed. Four to six should do. The actual NTP =
load is small compared to DNS queries.
3. Configure the local hosts as peers using the stratum one set as =
servers. Use crypto authentication if you feel the need.
4. Add NTP monitoring to your network management process.
5. Advertise the local time servers to your network - DHCP, word of =
mouth, configuration requirements, configuration scripts, standard =
builds, etc.
It is simple enough to do for a five node home network. It is almost =
that simple for a network with hundreds of thousands of client nodes. =
I've done both.
On Oct 24, 2010, at 12:29 PM, Brandon Kim wrote:
>=20
> I guess what I'm trying to understand is, is having your own NTP =
server just a luxury?
>=20
> I personally would like to have my own, I just need to pitch its =
advantages to my company. Unless everyone here on the NANOG group
> clearly spells it out to me that it's a luxury.
>=20
> I can see it as an added service/benefit though to our customers.....
>=20
>=20
>=20
>> Date: Sun, 24 Oct 2010 17:55:22 +0200
>> From: eugen@leitl.org
>> To: nanog@nanog.org
>> Subject: Re: NTP Server
>>=20
>> On Mon, Oct 25, 2010 at 02:51:24AM +1100, Ben McGinnes wrote:
>>=20
>>>> How do you knew that your local NTP server knew what time it is? =
(for sure)
>>>=20
>>> By polling as many stratum 1 and 2 time servers as possible. Having
>>> your own stratum 2 server(s) beats nebulous NTP servers out in the =
big
>>> bad Internet every time.
>>=20
>> For those you care about that:=20
>>=20
>> http://leapsecond.com/time-nuts.htm
>>=20
> =3D
James R. Cutler
james.cutler@consultant.com
