Re: mech-v2-05pre

[Fred Templin <osprey67@yahoo.com>]

Pekka,

--- Pekka Savola <pekkas@netcore.fi> wrote:

> On Thu, 26 Aug 2004, Fred Templin wrote:
> > --- Pekka Savola <pekkas@netcore.fi> wrote:
> > > Of course, if there's another spec down the road which modifies 
> > > proto-41 configured tunnels behaviour somehow so that other IP 
> > > protocols than just "6" are OK, that's fine as well.  The question is 
> > > just about whether unmodified configured tunnels could support 
> > > protocols other than "6", which doesn't seem to be the case..
> > 
> > As far as I can tell, no one is suggesting *support* for protocols
> > other than "6".
> > 
> > The suggestion is for the specification to declare as out-of-scope
> > the behavior for packets discovered to have version other than "6"
> > after the encapsulating IPv4 header is discarded.
> 
> Right, and in such a case there'a very little difference to just
> specifying drop here (and specifying the other protocols elsewhere),
> or declaring it out of scope (and implying a drop and specification
> elsewhere).

Drop silently? Drop and send an ICMPv4 error? Drop and send
an ICMPv6 error? Drop and do something else? By specifying
drop here, the behavior needs to be clearly spelled out to
avoid interoperability issues.

It seems both unambiguous and correct to say that if the version
is "6" and the payload is not at least 40 bytes, the packet MUST
be silently discarded. (Reason: there is no error from the IPv4
perspective, and there is not enough information to construct an
ICMPv6 error.) The same cannot be said for versions other than
"6", which argues for declaring out of scope.

Suggest re-wording the text as follows:

   "If the version encoded in the first 4 bits of the encapsulated packet
   is "6", and the payload is not at least 40 bytes in length (i.e., the
   minimum IPv6 packet), the packet MUST be silently discarded.  Further
   processing for packets with version other than "6" is out of scope."

Fred L. Templin
osprey67@yahoo.com