It would seem like ICMP timestamping is quite a useful feature for troubleshooting networks with asymmetric paths.

Replies to icmp(4) timestamp requests are generated by the kernel:

  • On OpenBSD, the feature is controlled by sysctl net.inet.icmp.tstamprepl, which is enabled by default.

  • FreeBSD even has no option to disable only the timestamp feature of ICMP (see case ICMP_TSTAMP in icmp_input())

On OS X, the respective setting is net.inet.icmp.timestamp, which is specifically disabled by default. Why?


The ICMP timestamp response contains the remote host's date and time. This information could theoretically be used against some systems to exploit weak time-based random number generators in other services

  • But most modern systems have clocks set to the same time within a few seconds -- and I think Mac OS X even synchronizes using NTP by default. – user1686 Nov 27 '13 at 12:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.