NTP packets travelling back in time?

Yes, negative delay in ntpd. Packets travelling back in time when going from the server to your client. Fasten your seat belts people, Captain Kirk is back šŸ˜‰

OK, seriously now. As you can expect, I was quite surprised to see this, but it appears to be expected in certain conditions.

Here's the full story. …One day I ran ntpq -c pe -c as on one of our clients, and I found out that the delay was negative for three out of fours servers (real IPs concealed):

$ ntpq -c pe -c as
      remote           refid      st t when poll reach   delay   offset  jitter
 -     3 m   66   64  376   -3.302    1.517   0.022
 +     3 m   63   64  376   -6.828    0.083   0.025
 +      3 m   54   64  376   -7.786   -0.756   0.035
 *     3 m   50   64  376    0.314    0.609   0.031
 ind assid status  conf reach auth condition  last_event cnt
   1 61991  731a    no   yes   ok    outlyer    sys_peer  1
   2 61992  741a    no   yes   ok  candidate    sys_peer  1
   3 61993  741a    no   yes   ok  candidate    sys_peer  1
   4 61994  761a    no   yes   ok   sys.peer    sys_peer  1

As you can imagine, I was a lot surprised… how could it be?

I posted my question to the relevant list, asking if it was a bug.

I got some contrasting answers. Some think I actually hit a bug. Others are less sure. But the bottom line seems clear: it is… well, "normal", it could happen in a multicast setting.

We'll wait and see if 4.2.8 fixes it.


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