clockdiff(8) -- Linux man page
NAMEclockdiff - measure clock difference between hosts
clockdiff [ -o] [ -o1] destination
- 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).
- 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.
- Some nodes (Cisco) use non-standard timestamps, which is allowed by RFC, but makes timestamps mostly useless.
- 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.
- clockdiff shows difference in time modulo 24 days.
 ICMP ECHO, RFC0792, page 14.
 ICMP TIMESTAMP, RFC0792, page 16.
clockdiff was compiled by Alexey Kuznetsov <firstname.lastname@example.org>. It was based on code borrowed from BSD timed daemon.
clockdiff is part of iputils package and the latest versions are available in source form for anonymous ftp ftp://ftp.inr.ac.ru/ip-routing/iputils-current.tar.gz.