[ntp:questions] Re: "Listen on" semantics

Luc Pardon xntp at skopos.be
Thu Sep 21 07:43:55 UTC 2006

Harlan Stenn wrote:

 >>> The client should keep my clock on track. The server should tell all my
 >>> other systems what time it is.
 > As I understand it, that is not the ntp model, that is the timed model.
      My understanding is that timed is a master/slave model, where one 
host on a LAN takes the lead and the others take their time from it. 
When the master dies, the slaves hold an election among themselves and 
the winner becomes the new master.

    What I meant by "client" is a some process that obtains the time 
from another process that provides it. In that sense, the timed slave is 
a client to its master, ntpd (at lest the part that sets the local 
clock) is a client to multiple servers (selecting the best), and sntp is 
a client to a single predefined server.

 > When peering, ntpd exchanges time packets with other ntpd processes 
on other
 > machines.
     True, and when in peer mode ntpd must indeed listen "in server 
mode" for packets from its peers. So, if you're peering across the open 
Internet, you must listen on the public interface. But if all the peers 
are internal, there is - again - no need to listen to the outside world.

 > We can get close to what you want today - run ntpd on your peering/master
 > machines, and sntp on your client/leaf machines.
     Functionally, yes. But that doesn't make me sleep any better. It's 
precisely about ntpd on the master box that I'm concerned. The leafs are 
shielded from the open Internet anyway, I don't mind running (x)ntpd there.


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