Internet Core Protocols: The Definitive Guide

Timestamp Request and Timestamp Reply query messages

Another pair of ICMP query messages that can be useful for testing the network is the Timestamp Request and Timestamp Reply query messages, which allow a sender to determine the amount of latency that a particular network is experiencing. This gives good insight into the performance characteristics of the network.

As can be imagined, this information also provides more insight than most people want to provide, at least to users outside the local network. For this reason, RFC 1122 states that the Timestamp Request and Timestamp Reply query messages are entirely optional. Indeed, there are only a few TCP/IP implementations that support them.

Timestamp works by having one system send a Timestamp Request query message to another host, with the current time in the Timestamp Request message’s Originate Timestamp field. The recipient then creates a Timestamp Reply query message that contains the Originate Timestamp field from the original message, along with new Receive Timestamp and Transmit Timestamp fields.

Once the Timestamp Reply query message is received by the querying device, the different timestamps can be examined, allowing the system to determine the amount of time that it took for the remote system to process the Timestamp Request query message. This data can then be subtracted from the round-trip delivery time, allowing the system to calculate the length of time that it took for the datagrams to travel across the network. ...