clockdiff [ -o] [ -o1] destination
clockdiff Measures clock difference between us and destination with 1 msec resolution using ICMP TIMESTAMP  packets or, optionally, IP TIMESTAMP option  option added to ICMP ECHO. 
|-o||Use IP TIMESTAMP with ICMP ECHO instead of ICMP TIMESTAMP messages. It is useful with some destinations, which do not support ICMP TIMESTAMP (f.e. Solaris <2.4).|
|-o1||Slightly different form of -o, namely it uses three-term IP TIMESTAMP with prespecified hop addresses instead of four term one. What flavor works better depends on target host. Particularly, -o is better for Linux.|
|o||Some nodes (Cisco) use non-standard timestamps, which is allowed by RFC, but makes timestamps mostly useless.|
|o||Some nodes generate messed timestamps (Solaris>2.4), when run xntpd. Seems, its IP stack uses a corrupted clock source, which is synchronized to time-of-day clock periodically and jumps randomly making timestamps mostly useless. Good news is that you can use NTP in this case, which is even better.|
|o||clockdiff shows difference in time modulo 24 days.|
 ICMP ECHO, RFC0792, page 14.
 ICMP TIMESTAMP, RFC0792, page 16.
 IP TIMESTAMP option, RFC0791, 3.1, page 16.
clockdiff was compiled by Alexey Kuznetsov <email@example.com>. It was based on code borrowed from BSD timed daemon.
clockdiff requires CAP_NET_RAWIO capability to be executed. It is safe to be used as set-uid root.
clockdiff is part of iputils package
and the latest versions are available in source form for anonymous ftp