[ntp:questions] server's address in ntp payload?

Danny Mayer mayer at gis.net
Fri Nov 18 14:24:34 UTC 2005


Ulisses wrote:
> Hello Danny
> 
> On Thu, Nov 17, 2005 at 09:29:17PM -0500, Danny Mayer wrote:
> 
>>Ulisses wrote:
>>
>>>Hello all
> 
> [...]
> 
>>No you are not wrong, but why would you want to? 
> 
> 
> The usefulness I wanted with it is to try getting the
> loopback address of ntp servers running on routers
> 

That's confusing me. Do you really mean the loopback addresss -
127.0.0.1 and ::1 or did you mean an address bound to the interface?

> (for good purposes)
> 
> Also It would be useful if I could extract from ntp, any 
> Globally Unique Identifier I could get from NTP protocol that
> could identify the same ntpd process in a multi-homed router.
> 

There nearest thing to an identifier is the refid. Unfortunately it's
flawed in the NTP reference implmentation since you can get different
refid's from different addresses on the machine.

> The only reliable way to achieve it I have figured out is 
> (more or less) to extract the ntp stats and compare them when 
> possible
> 
> 
>>Are you asking about the server sending the packet? 
> 
> 
>  Host A                         Host B (Router)
> 
>                      query
> ntpdc/ntpq/ntpd --------------> ntpd
>                 <-------------
>                      reply
> 
> I want to know from Host A, the address of Host B looking an ntp header
> 

I don't understand. Are you asking that, sitting at Host A, you send a
packet to host B and then you get in the response the address that Host
B sees as receiving the request from?

The answer is that it's the address of the interface receiving the
packet. There was a bug, long since fixed, which resulted in a packet
being returned to a different address.


Danny



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