Subject: Re: Flow Label

From: Margaret Wasserman <[email-masked]>
Date: Thu, 03 Jan 2002 14:51:00 -0500

Hi George,

Yes, we are "humming" in agreement to the proposal that we
replace section 6 of RFC 2460 with the following text:

 > The 20-bit Flow Label field in the IPv6 header MAY be set by a 
 > source to label sets of packets. Nodes that do not support 
 > the Flow Label field MUST set the field to zero when originating a 
 > packet, and MUST ignore the field when receiving a packet. All routers 
 > MUST pass the field on unchanged when forwarding a packet. 
 > 
 > This specification does not further define the meaning of the 
 > Flow Label. 
 > 

And that we delete Appendix A from RFC 2460.

Actually, we probably won't update RFC 2460.  We'll probably
just publish a separate RFC that updates 2460.

Margaret

At 02:01 PM 1/3/02 , [email-masked] wrote:
>Just a quick question from an interested lurker: Are these hums of
>acquiescence in response, specifically, to the idea that an originating
>node may set the flow label to any value, and that nodes forwarding
>packets will leave that value alone?              -- George Mitchell
>
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---

From: Randy Bush <[email-masked]>
Date: Fri, 04 Jan 2002 07:35:50 -0800

> And, truth in advertising, we have heard two dissenting
> views:
> 
> a) that the field should be defined as MUST BE ZERO, i.e.
> the MAY clause below gets deleted

fwiw, i withdraw my dissent

randy

---

From: Keith Moore <[email-masked]>
Date: Thu, 03 Jan 2002 14:51:30 -0500

> packets will leave that value alone?              -- George Mitchell

not quite.  if we someday define how the flow label is to be used, 
originating nodes can follow that spec.  that's not the same thing 
as saying that originating nodes can set the flow label field to 
whatever value they like.

Keith

---

From: Brian E Carpenter <[email-masked]>
Date: Fri, 04 Jan 2002 11:41:50 +0100

b) that the 3rd MUST should be SHOULD, i.e. immutability should
be default instead of mandatory.

   Brian

---

From: "Charles E. Perkins" <[email-masked]>
Date: Fri, 04 Jan 2002 09:40:45 -0800

Typo alert in my last message:

"Charles E. Perkins" wrote:

>    ...   So I would hope for a MUST here.  Language suggesting that
> it is merely the default would allow for a tunable know in the user
                                                     knob
> interface labeled thusly:
           ...

Regards,
Charlie P.

---

From: [email-masked]
Date: Thu, 3 Jan 2002 11:01:41 -0800 (PST)

---

From: Robert Elz <[email-masked]>
Date: Fri, 04 Jan 2002 20:17:56 +0700

Date:        Fri, 04 Jan 2002 11:41:50 +0100
    From:        Brian E Carpenter <[email-masked]>
    Message-ID:  <[email-masked]>

  | b) that the 3rd MUST should be SHOULD, i.e. immutability should
  | be default instead of mandatory.

I'm not sure I believe the 100% immutable argument, but I certainly
wouldn't deviate from it that far.  That is, I'd keep it at MUST
with just a very precise exception (which amounts to when the sender
has specifically notified the router that the field may be changed).

I'm pretty sure I'd never want to actually use the exception, except
possibly to explicitly say "Do what you like" (or if you like, "this
field isn't being used") - but I can't see what harm would be done
by leaving that small exception available.   In practical cases,
explicitly notifying routers about specific flows where the label
may be altered is most likely too difficult to ever happen, so this would
probably just amount to allowing a single router to change the field
from a sender's explicit "I don't care" into some other value.

kre