[ntp:questions] SNTP server + ntpd 4.2.4 client

Danny Mayer mayer at ntp.isc.org
Sun Mar 23 01:42:48 UTC 2008

Unruh wrote:
> "Richard B. Gilbert" <rgilbert88 at comcast.net> writes:
>> Danny Mayer wrote:
>>> Harlan Stenn wrote:
>>>> David> NTP clients must use NTP servers, not SNTP ones.
>>>> I do not believe this is true.
>>> Correct.
>>>> The problem is one might want to *know* that the SNTP server is actually
>>>> talking to a refclock, or more generally, that the SNTP "instance" is
>>>> playing by the rules.
>>> There is no way to ensure that. Furthermore there is nothing in the 
>>> protocol which allows you to differentiate between the two. This is 
>>> really a non-starter.
>>> Danny
>> I can't say it's worth doing but you could always add some sort of a tag 
>> to the NTP packet that says "I am an NTP server" or "I am an SNTP Server 
>> with a reference clock" or "I am an SNTP leaf node and I'm not supposed 
>> to talk to you"
> Look, an SNTP client is not supposed to act as a server. Period. If it does
> it means whoever programmed it broke the rules. Do you really thing having
> him program in an extra flag saying "I did not break the rules" is going to
> do anything? It is the same person who programmed it in the first place who
> also programs what it sends out in the packet.  
> An sntp client is not supposed to respond to server requests. You want it
> to respond. Why? I would think that the "flag" of no-response is far more
> effective than some bit in the packet.

I'm going to need to point you to the RFC draft for the definition of an 
SNTP server. However, no RFC will prevent anyone from writing code that 
allow an SNTP client also serving that time to other clients. The 
Internet police just aren't up to the task. That's the difference 
between an RFC and reality.


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