Network Time Protocol Version 4 (NTPv4) Extension Fields

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Last updated 2017-05-17 (latest revision 2016-11-13)
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Network Time Protocol version 4 (NTPv4) defines the optional usage of extension fields. An extension field, as defined in RFC 5905 [RFC5905], resides after the end of the NTP header, and supplies optional capabilities or information that is not conveyed in the standard NTP header. This document updates RFC 5905 [RFC5905] by clarifying some points regarding NTP extension fields and their usage with legacy Message Authentication Codes (MACs). With the adoption of this update, the authors recommend rescinding [Err3627].


Tal Mizrahi (
Danny Mayer (
Harlan Stenn (

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)