Re: Revision of draft-gont-6man-ipv6-universal-extension-header

["C. M. Heard" <[e-mail]>]

On Mon, 21 Apr 2014, Fernando Gont wrote:
> > The paragraph above does use the word "node" rather than "host" but 
> > in the context of RFC 2460 it does refer specifically to an end 
> > system ("the node [...] identified in the Destination Address field 
> > of the IPv6 header").
> 
> Not really. It could be a router, if the packet used a Routing Header.

True, but that does not change my main point: end systems are 
required by 2460 to discard any extension header they don't 
understand, so a UEH does not help them work better.  The problem it 
solves is that of middleboxes being unable to find the upper-layer 
header.

> > As far as I am aware, there have been no updates to the IPv6 
> > specifications requiring or even suggesting that end systems should 
> > ever try to skip over extension headers that they do not recognize.  
> > The problem exists only for middleboxes that examine and act on 
> > extension headers, so I recommend that this draft drop all 
> > discussion of end systems.
> 
> I understand your point. Me, I think it would be worthwhile to note that
> you cannot really "incrementally deploy" new EHs... at least without an
> Universal Extension Header.

Yes, that's true, since the barrier to incremental deployment is 
that middleboxes can't presently parse past them.

> > Furthermore, I don't see how the extension header problem discussed 
> > in this draft impedes deployment of transport protocols.  To be 
> > sure, here are problems with middleboxes filtering out transport 
> > protocols that they don't know, but that is an issue even without 
> > extension headers.
> 
> Right now, there's the misleading assumption (confusion?) that you *can*
> parse past unknown EHs. I wouldn't be surprised if a middlebox that
> receives a packet with a new transport protocol assumes that the
> corresponding header is really an EH, and tries to parse it according to
> RFC6564, and hence discard th packet.

Point taken.

//cmh