Turning routers into hosts (Re: Death by extension header (was:RE: New Version Notification for draft-li-6man-hbh-fwd-hdr-00.txt))

On Tue, 14 Jul 2020 at 06:02, Toerless Eckert <tte@cs.fau.de> wrote:
>
> On Mon, Jul 13, 2020 at 03:00:44PM -0300, Fernando Gont wrote:
> > On 10/7/20 15:32, Toerless Eckert wrote:
> > > IMHO: See my email earlier in the thread about punting stuff to slow-path, especially when/before
> > > you figure out that you should have just ignored something at linerarte.
> > >
> > > Aka: not sufficiently prescriptive RFCs + bad implementations == extension header based features killed in deployments.
> >
> > Indeed. And add to that that the EH structure itself seems to be rather
> > unfriendly with some popular hardware architectures. (unless with "not
> > sufficiently prescriptive RFCs" you are meaning to set the maximum EH-header
> > chain length to some sane value that folks might agree to comply with).
>
> I think we might want to start with a draft collecting what we think to
> kow about the problem and figure out if we can structure it accordingl
> to make sense out of it to make progress that is not just incrementally fixing
> one single bit.
>

I think one of the first sections needs to be titled:

"Turning Routers into Hosts"

because in-flight processing of packets' EHs, payloads etc, rather
than just dumb, fast and simple forwarding them, is host processing of
packets.

How to tell it's host processing?

- processing of packets requires going past the IPv6 fixed header

- in-flight processing would fail if everything but the fixed header
was encrypted

- processing beyond the fixed (forwarding) header is occuring at a
node that *doesn't* hold the packet's destination address:

RFC8200:

router       a node that forwards IPv6 packets not explicitly
                addressed to itself.  (See Note below.)

   host         any node that is not a router.  (See Note below.)

(Note is about a node's interfaces being forwarding or not)

In this discussion and similar, people are really discussing paths
between a packet's original source and a final destination constructed
of a set of packet host processing hops.

Regards,
Mark.

> Cheers
>     Toerless
>
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