Re: RFC 2434 term "IESG approval" (Re: IANA Action: Assignment of an IPV6 Hop-by-hop Option)

[Jeffrey Hutzelman <jhutz at cmu.edu>]

On Friday, July 01, 2005 07:58:42 AM +1000 grenville armitage 
<garmitage at swin.edu.au> wrote:

> Brian E Carpenter wrote:
>
> > Hans Kruse wrote:
> > ...
> >
> > > but otherwise I _cannot_ see how the _content_ of the option could
> > > harm a device that does not want to deal with it.
> >
> >
> > If it interferes with congestion management elsewhere along the path, it
> > can potentially damage
> > every other packet stream. This is a *very* complex discussion of course.
>
> I can see it interfering for two reasons. (a) The option codepoint clashes
> with the codepoint used by another congestion management mechanism
> (thereby
> confusing routers handling packet streams using the same codepoint
> differently),
> or (b) IPv6 option handling is flawed in so far as an unknown option
> turning
> up in a packet stream can totally mess with 'congestion management
> elsewhere
> along the path'.
>
> Scenario (a) would seem to be solved by assigned a non-conflicting option
> codepoint and then hoping the competing protocol dies of irrelevance.
> Scenario (b) suggests we have bigger problems. I'm honestly hoping it
> isn't
> scenario (b), and that there's an scenario (c) I'm just not seeing.



Have you read the spec in question?

The issue is not that the presence of an unknown option interferes with 
congestion control.  The problem is that when the endpoints _do_ implement 
the option, they can sometimes decide to disregard TCP congestion control 
procedures such as slow-start, which while implemented on an end-to-end 
basis nonetheless affect congestion control on all intervening segments.

Now, it's possible that, in the circumstances in which this spec allows 
endpoints to punt on slow-start, it is actually safe to do so without 
risking causing problems for the rest of the network.  But I haven't read 
the document in enough detail to know that, and the potential for problems 
if it is not is quite large.  I'd be much happier if any proposal along 
those lines were reviewed by the IETF (particularly, experts in IPV6, QOS, 
TCP, congestion control, etc) before being unleashed on the Internet.


-- Jeffrey T. Hutzelman (N3NHS) <jhutz+ at cmu.edu>
  Sr. Research Systems Programmer
  School of Computer Science - Research Computing Facility
  Carnegie Mellon University - Pittsburgh, PA


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