Using UDP Checksum Trailers in the Network Time Protocol (NTP)

Document Type Replaced Internet-Draft (candidate for ntp WG)
Last updated 2014-07-31 (latest revision 2014-04-15)
Replaced by RFC 7821
Stream IETF
Intended RFC status (None)
Expired & archived
pdf htmlized (tools) htmlized bibtex
Stream WG state Call For Adoption By WG Issued
Document shepherd No shepherd assigned
IESG IESG state Replaced by draft-ietf-ntp-checksum-trailer
Consensus Boilerplate Unknown
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Responsible AD (None)
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


The Network Time Protocol (NTP) allows clients to synchronize to a time server using timestamped protocol messages. To faciliate accurate timestamping, some implementations use hardware-based timestamping engines that integrate the accurate transmission time into every outgoing NTP packet during transmission. Since these packets are transported over UDP, the UDP checksum field is then updated to reflect this modification. This document proposes an extension field that includes a 2-octet Checksum Trailer, allowing timestamping engines to reflect the checksum modification in the last 2 octets of the packet rather than in the UDP checksum field. The behavior defined in this document is interoperable with existing NTP implementations.


Tal Mizrahi (

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