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?

1 Answer 1


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.
    – grawity
    Commented Nov 27, 2013 at 12:20

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