Internet Core Protocols: The Definitive Guide

Name

Timestamp Request and Timestamp Reply

Synopsis

The ICMP Timestamp Request and Timestamp Reply query messages provide the ability to determine the length of time that ICMP query messages spend in transit, which is extremely useful for measuring the latency across a specific network.

ICMP Message Type

The Message Type for Timestamp Request is 13. The Message Type for Timestamp Reply is 14.

ICMP Message Codes

Neither the Timestamp Request nor Timestamp Reply query messages use any Codes, and this field must be zero.

Defined In

RFC 792.

Additional Fields

Both the Timestamp Request and Timestamp Reply query messages use the same message structure. The additional fields used by these messages are shown in Table 5.13.

Table 5.13. Additional Fields in Timestamp Request and Timestamp Reply

Field	Bytes	Description
Identifier	2	Provides a “session identification number” for the request and reply messages.
Sequence Number	2	Provides a “counter” for requests and replies, allowing multiple messages to be used with a single Identifier.
Originate Timestamp	4	The exact time that the Timestamp Request query message was sent.
Receive Timestamp	4	The exact time that the Timestamp Request was received by the final destination system.
Transmit Timestamp	4	The exact time that the Timestamp Reply was sent back.

These fields are explained below:

• The Identifier field provides a kind of “session identification number” for the Timestamp Request and Timestamp Reply query messages being passed between various hosts. For example, if ...