[ntp:questions] ntp server pool advice

Terje Mathisen "terje.mathisen at tmsw.no" at ntp.org
Thu Dec 22 11:44:07 UTC 2011


ben slimup wrote:
>
> Thank for prompt answer Chris,
>
> Unfortunately, this ntp network should give time to specific clients
> devices and not anyone on the public network.
>
> according to your advice, better not using load balancer, thats good
> how to load balance between ntp server if i do not use round robin?
> if all client choosing the same server then the ntp server will be
> overload. is it a problem if for example client 1  poll or synch with
> server 1 , and then with server 2 , etc...? or udp roundtrip comes
> each time from different ntp server? how many ntp servers should be
> needed to handle that much request knowing that each card handle
> 10,000 request per sec?

First, each client should have at least 4 configured servers, so you can 
use the same ntp.conf file for all of them.

Second, if you really can handle 10K requests/second per card, then that 
means that you can handle 640K clients per card, with worst-case polling.

I.e. servers capable of 10K/second should handle your expected load just 
fine, even though a proper (FreeBSD-based) 1U server with a GPS will 
serve even more clients with better time performance.

Terje
>
> much appreciate your expertize
>
> cheers
>
>> From: albertson.chris at gmail.com Date: Wed, 21 Dec 2011 19:43:53
>> -0800 Subject: Re: [ntp:questions] ntp server pool advice To:
>> slimup78 at hotmail.com
>>
>> On Wed, Dec 21, 2011 at 5:07 PM, ben slimup<slimup78 at hotmail.com>
>> wrote:
>>>
>>> Dear all,
>>>
>>> Thank you very much for support,
>>>
>>> i do not have 1000,000 client, i need those ntp servers to serve
>>> a load  between 100000 to 1000000 clients over a public network
>>> with an accuracy of 100ms
>>>
>>> those clients will use dns round robin to resolve 4 external ip,
>>> 2 IPs on each site. i have 4 servers with 4 ntp server slot card
>>> each ( meinberg M900) 1 ntp server card can support 10,000
>>> request.
>>
>> First off the good news.  100ms is an "easy" spec to meet you can
>> do this without a lot of effort.
>>
>> Don't let the outside world "see" your meinberg servers.    Build
>> out a layer of "statum 2" servers and expose those to your clients.
>> 1M clients is a lot for the little 386 class CPU that is in the
>> meinberg box.
>>
>> I still don't understand, Why do all those NTP clients need to go
>> to your NTP servers. Why can't they use any they like?    Are your
>> servers doing something special?
>>
>> Also know that EACH client needs to be configured to see multiple
>> NTP servers.  practically three servers is a minimum but others
>> will argue for more for five
>>
>> A would not use load balancing for NTP servers.    With NTP it
>> does not matter at all if a server crashes.  The clients are all
>> configure to use five servers and if one crashes they will do fine
>> using four. If you expose four, large robust servers one on each of
>> your four IP addresses then you will be fine, even if one fails you
>> will be fine. The clients will notice the failure and continue on
>> using the remaining three.
>>
>>
>> I technical question for the list:  Would Round Robin load
>> balancing even work.  I think it would introduce so much jitter the
>> server would be  usless.  I think you have to be sure that each
>> time a client pools a server at a given IP address it polls the
>> same physical server.
>>
>> Chris Albertson Redondo Beach, California


-- 
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"



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