Re: GIST Q/D-mode issue

On Wednesday 10 September 2008 17:53:48 Hancock, Robert wrote:
> first, a couple of general points:
>
> - at the conceptual level, i think we should distinguish
> between (a) whether a message is sent in Q- or D-mode, and
> (b) whether a message has to be interpreted when received
> in the absence of routing state. in the current spec, either
> of these classify messages the same way, but the concepts
> are distinct: (a) is about sender behaviour [mainly, formatting
> the message to follow a data path] and (b) is about
> receiver behaviour [knowing how to decode what you get].
...
> in another mail:
> > Max Laier proposed option 4):
> > use a different magic number for Q-Mode and D-Mode messages.
> > Any opinions?
>
> i don't really like this. i have generated the appropriate
> random number (4d62 8fa0), but it still seems like a hack.
> and the same issues about extensibility apply.

I agree and after reading the above realize that my idea would better serve as 
a solution for your point (b) above.  Without the RAO as a simple indication 
when to break the forwarding fast path and hand the packet up the stack for 
more careful inspection it can get really expensive - i.e. you have to hand 
every single D-mode packet all the way up to userland just to figure out that 
you are not interested.  If we were to use a magic number to differentiate 
case (b) it becomes much simpler to perform the interception decision at a 
lower level (e.g. with a bpf filter rule or the like).

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