[ntp:questions] Re: Peer configuration question?

Richard B. Gilbert rgilbert88 at comcast.net
Fri Jan 30 22:47:20 UTC 2004


Well, I'm less certain of my ground here but here goes.

 I believe that stratum takes precedence over preference.  (someone 
please correct me gently if I'm wrong).  A server with a lower stratum 
will be used before a higher stratum that is preferred.

Peers and servers within the same stratum start out as equals.  The 
selection algorithms will be applied equally to all of them.  Remember 
that the only difference between peers and servers is symmetry or 
asymmetry in their relationship with you.

Read RFC1305 or as much of it as you can understand.  Read the 
documentation for the reference implementation, and observe your servers 
and clients in action.  When you see behavior you don't understand, ask.

Nicholas Garfield wrote:

>Richard,
>
>Thanks for such a concise reply.  You have summed up nicely what I wanted
>confirming about peers.....
>so how does the "prefer" statement effect this scenario?  Suppose you have a
>preferred "server" and a non-preferred "peer".
>Will the server always win?  Suppose neither are "preferred", will the
>"peer" always take precedence over a server?
>I realize this is probably just pedantic, but I really want to understand
>the dynamics of such a system.
>
>Thanks
>
>Nick
>
>
>"Richard B. Gilbert" <rgilbert88 at comcast.net> wrote in message
>news:OcednU09jIRVAITdRVn_iw at comcast.com...
>  
>
>>The difference between peers and servers is very simple!
>>
>>Peers have a symmetric association; either one can supply time to the
>>other.  If two peers have different opinions as to what time it is, they
>>will try to determine who has the more accurate time and both will use
>>that time.
>>
>>Servers are asymmetric; a server can supply time to you but will not
>>accept time from you.
>>
>>For maximum reliability, you would have your two stratum 1 servers
>>configured as peers.  If everything is working properly, these two
>>servers should track each other and the "correct" time within a few
>>microseconds.  If either GPS receiver fails, the server it is connected
>>to will obtain the correct time from its peer and continue to serve its
>>clients.  If you have a network neighbor who also operates stratum 1
>>servers you might wish to peer with his servers as well.  A setup like
>>that gives you both a defense in depth against failures of reference
>>clocks, or servers.
>>
>>Configure your stratum 2 servers to peer with each other and to be
>>served by both stratum 1 servers.  All clients should be served by the
>>stratum 2 servers.
>>
>>Your single point of failure would be the GPS satellite system itself.
>>Highly unlikely but the DOD could just pull the plug on all those
>>satellites. . . .
>>
>>
>>Nicholas Garfield wrote:
>>
>>    
>>
>>>Hi All,
>>>
>>>I have two stratum 1 servers which are each connected to Trimble Accutime
>>>GPS receivers.  Then two more servers use these sources as stratum 2
>>>servers.
>>>I have been reading the NTP FAQ Section 6.2. Advanced Configuration,
>>>      
>>>
>however
>  
>
>>>I am unsure of the configuration.
>>>
>>>(1) For the stratum 1 servers, should there be a peering relationship
>>>between them?
>>>
>>>ie on server 1 config is
>>>
>>>server 127.127.29.0 prefer minpoll 4 maxpoll 4 #ACCUTIME
>>>peer 192.168.17.69 version 4 minpoll 4 maxpoll 4 #SERVER 2
>>>
>>>On server 2 config is
>>>
>>>server 127.127.29.0 prefer minpoll 4 maxpoll 4 #ACCUTIME
>>>peer 192.168.18.69 version 4 minpoll 4 maxpoll 4 #SERVER 1
>>>
>>>Also, would someone be kind enough to clarfiy whether or not the "prefer"
>>>keyword is necessary here.  I figure (probably incorrectly) that I would
>>>prefer the time to come from the accutime, but how would this work with
>>>      
>>>
>the
>  
>
>>>idea of selecting the "best" clock.
>>>
>>>(2) Similarly the config for the stratum 2 servers uses peering.
>>>
>>>I am not 100% clear what the difference between a "server" declaration
>>>      
>>>
>and a
>  
>
>>>"peer" declaration is.  When a server and a peer is specified how does
>>>      
>>>
>ntp
>  
>
>>>choose which is preferred?
>>>
>>>Thankyou in advance to anyone who can explain clearly when/where the peer
>>>and prefer statements should/should not be used.
>>>
>>>Regards
>>>
>>>Nick
>>>
>>>
>>>
>>>
>>>      
>>>
>
>
>  
>



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