+1 - this articulates my concerns and what I'd like to see done to resolve.

Wes George

-----Original Message-----
From: ipv6-boun...@ietf.org [mailto:ipv6-boun...@ietf.org] On Behalf Of John 
Leslie
Sent: Monday, May 09, 2011 7:27 PM
To: Brian E Carpenter
Cc: ipv6@ietf.org; RJ Atkinson
Subject: Re: Flow label drafts updated

Brian E Carpenter <brian.e.carpen...@gmail.com> wrote:
> On 2011-05-10 01:02, RJ Atkinson wrote:
>  
>> A much more reasonable approach would be to say (edit to taste):
>> 
>>      "The Flow Label SHOULD NOT be changed in transit." 
> 
> The authors really need to hear that from more than one person, or to 
> hear from the WG Chairs that it's a consensus, because it goes against 
> several months of discussion.

   I agree with Ran that SHOULD NOT is more appropriate for this case where the 
horse has long since left the barn. Middleboxes
_are_ going to clear it (or worse).

   OTOH, I don't actually _object_ to MUST NOT -- in the narrow sense that any 
node that disobeys the MUST NOT isn't speaking the
protocol as defined.

   I do believe we should, regardless, excise all use of the word "immutable" 
for the Flow Label. That word isn't helping.

> I suggest squaring this circle by retaining the MUST NOT (which IMHO 
> is the present consensus) but making it clear in the security 
> considerations that there will be exceptions. The problem here is that 
> the RFC 2119 language doesn't provide MUST NOT UNLESS..., which is 
> what we really need. SHOULD NOT is not perceived as strong enough.

   I could live with that; but I really do suggest wordsmithing the
3 uses of "immutable".

   Additionally, I'd like to see some treatment of what may go wrong if 
middleboxes change the Flow Label. If I understand, it will
partly break load-balancing. Middlebox designers probably don't understand this 
issue. (Even if they did, they'd likely say, "some
users are entirely willing to accept that tradeoff.")

--
John Leslie <j...@jlc.net>
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