Subject: [ntpwg] I-D Action: draft-ietf-ntp-extension-field-04.txt

From: [email-masked]
Date: Sat, 15 Aug 2015 23:35:03 -0700

A New Internet-Draft is available from the on-line Internet-Drafts directories.
 This draft is a work item of the Network Time Protocol Working Group of the IETF.

        Title           : The Network Time Protocol Version 4 (NTPv4) Extension Fields
        Authors         : Tal Mizrahi
                          Danny Mayer
	Filename        : draft-ietf-ntp-extension-field-04.txt
	Pages           : 7
	Date            : 2015-08-15

Abstract:
   The Network Time Protocol Version 4 (NTPv4) defines the optional
   usage of extension fields. An extension field, defined in RFC5905, is
   an optional field that resides at the end of the NTP header, and can
   be used to add optional capabilities or additional information that
   is not conveyed in the standard NTP header. This document updates
   RFC5905 by clarifying some points regarding NTP extension fields and
   their usage with Message Authentication Codes (MAC).

The IETF datatracker status page for this draft is:
https://datatracker.ietf.org/doc/draft-ietf-ntp-extension-field/

There's also a htmlized version available at:
https://tools.ietf.org/html/draft-ietf-ntp-extension-field-04

A diff from the previous version is available at:
https://www.ietf.org/rfcdiff?url2=draft-ietf-ntp-extension-field-04

Please note that it may take a couple of minutes from the time of submission
until the htmlized version and diff are available at tools.ietf.org.

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/

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From: Miroslav Lichvar <[email-masked]>
Date: Thu, 27 Aug 2015 15:12:59 +0200

> 	Filename        : draft-ietf-ntp-extension-field-04.txt

In the new text for the section 7.5. there is a sentence that is a bit
confusing to me:

   Note that
   in the presence of an unknown extension field any MAC that may be
   present may be misinterpreted as an unknown extension though in this
   case the apparent extension length will be inconsistent with the
   total length of the rest of the packet.

Wouldn't it be more clear if it said something like "any MAC longer than
24 octets thay may be present with the extension field may be
misinterpreted" ?

Also, the length in the misinterpreted extension field may happen to
be correct by chance, so maybe rather "the apparent extension length
will likely be inconsistent" ?

-- 
Miroslav Lichvar

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From: "Ulrich Windl" <[email-masked]>
Date: Thu, 27 Aug 2015 15:37:38 +0200

>>> Miroslav Lichvar <[email-masked]> schrieb am 27.08.2015 um 15:12 in
>    total length of the rest of the packet.

Terrible sentence! (an "if", two "may", one more restriction ("in case"))

> 24 octets thay may be present with the extension field may be

Still terrible! (two "may")

"MAC fields only work reliable with known extension fields due to a bad design decision that can't be undone without breaking compatibility."?