Subject: AD review of draft-ietf-6man-flow-update

From: Jari Arkko <[email-masked]>
Date: Mon, 20 Jun 2011 08:12:31 +0300

I have reviewed this specification. It is well written and ready to move 
forward; I have asked for an IETF Last Call.

I did have two very minor editorial comments, and one personal opinion:

> In this case too, the word
> "alone" is to be interpreted precisely - a router is allowed to
> combine the flow label value with other data in order to produce a
> uniformly distributed hash.
>   

I think this would be simpler if you had just said "But the word "alone" 
needs to be taken into account - a router is allowed ..."

(There is nothing precise or imprecise about this. You just can't bypass 
the key word from the rule.)

> The main novelty is that a forwarding node (typically a first-hop or
> ingress router) may set the flow label value if the source has not
> done so, according to the same recommendations that apply to the
> source.  This might place a considerable processing load on ingress
> routers, even if they adopted a stateless method of flow
> identification and label assignment.
>   

I'd prefer to replace the second sentence with "This might place a 
considerable processing load on ingress routers that choose to do so, 
even ..."

Finally, the personal opinion was that I'd probably have left four bits 
from the flow label as reserved values (set to zero on send; included as 
flow label bits for all other processing). I'm not asking you to change 
the approach or the draft, just stating that I would have left some room 
for future developments.

Jari

---

From: Brian E Carpenter <[email-masked]>
Date: Tue, 21 Jun 2011 01:01:26 +1200

Jari,

No problem with your editorial comments - they are small enough that
I suggest holding them until after the LC.

> four bits from the flow label as reserved values 

There was a pretty clear consensus against having any special bits, when
this sort of idea was discussed last year.

Thanks
   Brian

---

From: Jari Arkko <[email-masked]>
Date: Mon, 20 Jun 2011 21:14:29 +0300

Brian,

> this sort of idea was discussed last year.

Ok. Was there a rationale, e.g., that it would be impossible to do so 
for some reason, or that the bits could not be used?

Jari

---

From: Brian E Carpenter <[email-masked]>
Date: Tue, 21 Jun 2011 09:53:03 +1200

> for some reason, or that the bits could not be used?

I'd have to trawl the archive to find all the arguments, but the main issue
was that any attempt to include semantics in the bits of the flow label
leads to complexity that probably can't be handled at line speed in a scaleable
way. Also 16 bits might make it too easy for a malicious party to predict
flow label values.

   Brian