Subject: RE: I-D ACTION:draft-ietf-ipv6-default-addr-select-08.txt

From: "Richard Draves" <[email-masked]>
Date: Thu, 20 Jun 2002 20:23:44 -0700

> > The default is still to use public addresses not temporary 
> addresses, 
> > although implementations MAY reverse this default if they want to 
> > emphasize privacy over application compatibility.
> 
> 
> I'm wondering why having an escape clause that only apply
> to that particular rule.

First, note that most of the source address slection rules are SHOULD
requirements. (The "prefer matching scope" rule being an exception -
it's MUST.) An implementation can violate a SHOULD requirement - from
RFC 2119:
3. SHOULD   This word, or the adjective "RECOMMENDED", mean that there
   may exist valid reasons in particular circumstances to ignore a
   particular item, but the full implications must be understood and
   carefully weighed before choosing a different course.

So even without the explicit escape clause, an implementor could decide
given their implementation's particular circumstances to prefer
temporary addresses over public addresses.

Second, note that this escape clause has been there for more than a year
(since version 04) and already passed WG & IETF last calls.

The reason for having the explicit escape clause is that this rule has
been the subject of much discussion in the WG & IESG; some feel that
privacy is the overriding concern and some feel that application
compatibility is more important. We have a rough consensus to favor
application compatibility by default. But as a member of the privacy
camp, I think it's helpful to remind implementors that if in their
particular circumstances privacy is more important than app
compatibility, then they can prefer temporary addresses by default.

Rich

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From: Keith Moore <[email-masked]>
Date: Fri, 21 Jun 2002 00:08:19 -0400

> compatibility, then they can prefer temporary addresses by default.

the point is that the host implementation is almost the worst possible
place to override that default.    the app knows what kind of addresses
it needs, so it is in a good position to make such decisions.  the 
user understands his own need for privacy, but he probably doesn't 
understand the implications of such a decision for his apps,  so he's
not in the best position.  the host implementor knows even less than
the user - unless you are talking about appliance hosts cannot be
programmed by the user.  in the latter situation the app implementor
and the host implementor can be considered the same, and it's as easy
for the app to select the proper kind of address than for the host
implementor to do so.

so I can really find no clear case for having the host implementor
change the default.  

as you say, the SHOULD clause already allows an escape in the case
where the host implementor clearly understands the implications
of the decision - though that tends to require the host implementor
to understand what apps will be run on the host, since the implications
will vary from one app to another.

on the other hand the MAY clause doesn't require the host implementor
to understand those implications.  it would therefore be better to 
remove the MAY clause entirely.

Keith