ICMP packet with a negative round trip time? I often keep a ping running in my Terminal so that I can pop it up to keep an eye on any network issues in our office. Recently, I ended a long-running ping session and noticed in the summary statistics that the minimum round trip time was -520ms.



Does anyone have any explanations for this bug?
There are several possible explanations for negative ping times:


You are running OS X on a PC with a AMD Athlon™ 64 X2 Dual Core Processor which has a bug in the power management which may not only effect Windows but also OS X installations.
Google is tired of getting pinged 38325 times and is sending erroneous timestamps in the ICMP echo replies - simulating a relativistic twin paradox. The -520.236 ms echo reply packet pretends to come from the fast moving  "younger" twin server and the 7219027.621 ms echo reply is the silver-haired "grandpa" twin server standing still - both behind a misconfigured Einstein-Rosen voodoo load balancer!
ntpd did its work and adjusted the time while a ping was sent. This explains the negative time as well as the two-hour-ping: 7219027.621 ms are two hours and 19 seconds - the most prolonged ping I have ever seen!

You can reproduce it yourself by adjusting the time manually like in this ping listing:

64 bytes from 185.62.237.118: icmp_seq=17 ttl=55 time=290.491 ms
64 bytes from 185.62.237.118: icmp_seq=18 ttl=55 time=310.241 ms
64 bytes from 185.62.237.118: icmp_seq=19 ttl=55 time=-11797.674 ms
64 bytes from 185.62.237.118: icmp_seq=20 ttl=55 time=303.643 ms
64 bytes from 185.62.237.118: icmp_seq=21 ttl=55 time=326.527 ms


I turned the time back for several seconds while ping 19 was sent.