ICMPv4 Timestamp (Request) and Timestamp Reply Messages
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Issues Using Timestamp and Timestamp Reply Messages
In practice, even with three timestamp fields, it is difficult to coordinate system clocks over an internetworkespecially a large one like the Internet. The main problem is that the amount of time it takes to send a datagram between any pair of devices varies from one datagram to the next. And again, since IP is unreliable, it's possible the time for a datagram to be received could be infiniteit might be lost or dropped by a router.
This means that a simple exchange of Timestamp and Timestamp Reply messages is simply not a reliable enough method for ensuring that two devices are synchronized on a typical IP internetwork. For this reason, modern devices often use a more sophisticated method for time synchronization, such as the Network Time Protocol (NTP).
Note that unlike many of the other ICMP message types, support for Timestamp and Timestamp Reply messages is optional, for both hosts and routers.
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Version 3.0 - Version Date: September 20, 2005
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