[ntp:questions] Protocol exchange

skendric skendric at fhcrc.org
Fri May 4 15:30:15 UTC 2012


I'm trying to match what I see on the wire with what I read in
http://www.ietf.org/rfc/rfc5905.txt

The Server's response to the Client contains exactly the same values
for Reference Timestamp, Origin Timestamp, Receive Timestamp, and
Transmit Timestamp.

That doesn't make sense to me.

OK, I buy the idea that Reference and Origin Timestamp would be the
same in both the Request and Response packets ... but I would have
predicted that:
(a) The Client would leave the Receive and Transmit Timestamps blank,
rather than invent some numbers to put there
(b) The Server would do more than just echo back the Client's choice
for Receive and Transmit Timestamps ... like ... perhaps it would /
fill in/ its idea of time for both.

>From RFC 5905:
[...]
Reference Timestamp: Time when the system clock was last set or
   corrected, in NTP timestamp format.

   Origin Timestamp (org): Time at the client when the request
departed
   for the server, in NTP timestamp format.

   Receive Timestamp (rec): Time at the server when the request
arrived
   from the client, in NTP timestamp format.

   Transmit Timestamp (xmt): Time at the server when the response left
   for the client, in NTP timestamp format.

What I see on the wire:

NTP CLIENT (ntpd v4.2.4p8)
[...]
Network Time Protocol (NTP Version 4, server)
  Flags:  0x24
    00           = Leap Indicator:  no warning (0)
      10         = Version number:  NTP Version 4 (4)
           100  = Mode:  server (4)
  Peer Clock Stratum:  secondary reference (3)
  Peer Polling Interval:  10 (1024 sec)
  Peer Clock Precision:  0.000001 sec
  Root Delay:  0.0022 sec
  Root Dispersion:  0.0511 sec
  Reference ID:  foo.company.com
  Reference Timestamp:  May 3, 2012 19:43:56.186981000 UTC
  Origin Timestamp: May 3, 2012 19:52:55.069223000 UTC
  Receive Timestamp: May 3, 2012 19:52:55.071776000 UTC
  Transmit Timestamp: May 3, 2012 19:52:55.071805000 UTC

SERVER (v4.2.2p1):
[...]
Network Time Protocol (NTP Version 4, server)
  Flags:  0x24
    00           = Leap Indicator:  no warning (0)
      10         = Version number:  NTP Version 4 (4)
           100  = Mode:  server (4)
  Peer Clock Stratum:  secondary reference (3)
  Peer Polling Interval:  10 (1024 sec)
  Peer Clock Precision:  0.000001 sec
  Root Delay:  0.0022 sec
  Root Dispersion:  0.0511 sec
  Reference ID:  foo.company.com
  Reference Timestamp:  May 3, 2012 19:43:56.186981000 UTC
  Origin Timestamp: May 3, 2012 19:52:55.069223000 UTC
  Receive Timestamp: May 3, 2012 19:52:55.071776000 UTC
  Transmit Timestamp: May 3, 2012 19:52:55.071805000 UTC

i.e. Request and Response contain identical values for Receive and
Transmit ... this seems hard to believe to me.  Yes, Client and Server
are separated by a campus network which introduces <1ms of latency ...
but still, I would have expected these time stamps to vary.

What am I missing?

--sk

Stuart Kendrick
FHCRC



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