Subject: RE: I-D ACTION:draft-hinden-ipv6-global-local-addr-01.txt

From: "Peter Barany" <[email-masked]>
Date: Thu, 7 Aug 2003 09:53:42 -0500

Right, but what I am trying to get at is the wording "obtain the current
time of day" in 64-bit NTP format [NTP]. The phrase "current" implies some
degree of accuracy with regard to the notion of a wallclock (absolute date
and time) which is seconds relative to 0h UTC on Jan. 1,1900.

So, if a client has no notion of a wallclock, couldn't it set the current
time of day in 64-bit NTP format to zero? Or maybe it could simply use a
"system-specific" clock such as "system uptime". I haven't done any
simulations, but this would certainly increase the probability of a
collision (at least for locally assigned global IDs) ... granted, there is
probably still a very low probability of non-unique locally assigned global
IDs being generated by the algorithm.

Even if the client has a notion of a wallclock, the accuracy may be limited
to far less than the resolution that the 64-bit NTP format is capable of
representing ... so more zeros perhaps for the 32 bits to the right of the
decimal?

So if the algorithm is dependent upon "current time of day", I should think
that we would want some statement included in the document to the effect
that
(1) access to a wallclock or not
(2) running the Network Time Protocol not being required
(3) other time sources, or none at all, may be used, etc.   

Pete

-----Original Message-----
From: Brian E Carpenter [mailto:[email-masked]]
Sent: Thursday, August 07, 2003 7:01 AM
To: [email-masked]
Subject: Re: I-D ACTION:draft-hinden-ipv6-global-local-addr-01.txt

> Peter Barany wrote:
> 
> Hi,
> 
> Two questions about this I-D:
> 
> (1) In Section 3.2.3 "Sample Code for Pseudo-Random Global ID Algorithm",
step (1) of the algorithm states:
> "Obtain the current time of day in 64-bit NTP format (NTP)"
> Question: Would it be possible to have the I-D specify that "how the
current time of day is obtained is beyond the scope of
> this document"?

What is specified is the format, not the source. It's necessary to specify 
a format in order to specify an algorithm.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Brian E Carpenter 
Distinguished Engineer, Internet Standards & Technology, IBM 

NEW ADDRESS <[email-masked]> PLEASE UPDATE ADDRESS BOOK
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