architected shim layers [was Re: threats ID]

[Brian E Carpenter <brc@zurich.ibm.com>]

Masataka, please moderate your language. I understand layering
well enough to know that the layers in the OSI model are very
abitrary choices, and a better model would have been a recursive
one, with no predefined number of layers. Since that's not the
model the industry chose to adopt, we can approximate it by
inserting shim layers when we need to. 

NAT is indeed a defective shim layer, but what this WG has been
mainly talking about is architecturally designed shims.

   Brian

Masataka Ohta wrote:
> 
> Brian;
> 
> > Masataka, you conclude by saying
> >
> >
> >>However, TCP is not IP, which is the point of my presentation
> >>at Vienna.
> >
> >
> > We can hardly disagree. But TCP is not SCTP, UDP, DCCP or ICMP either.
> 
> That's why TCP is not IP.
> 
> > The systems level argument for a layer 3.5 solution
> 
> There is no such thing as layer 3.5.
> 
> Network layer solutions are at layer 3, transport layer solutions are
> at layer 4. PERIOD.
> 
> > is that it can cover
> > all cases, including ones we have not invented yet.
> 
> UDP, which we already invented, can not be covered by network
> layer solutions.
> 
> > You are correct that a layer 3.5 solution requires cached state, probably
> > with timeouts
> 
> Anything with wrongly guessed timeout is no solution.
> 
> > There is a classical
> > solution to that, which is for the ULP to send a keepalive signal to prevent
> > the cache from timing out.
> 
> That is a modification to the ULP, including application ones and
> is substantial.
> 
> That you must modify something above layer 4 gives a very convincing
> evidence, even for those who don't understand layering enough to dream
> of layer 3.5, that layer 3.5 is a fallacy.
> 
> > That would indeed be a ULP enhancement, but a very
> > minor one and not essential.
> 
> That is a well known argument for NAT.
> 
> However, it is not an enhancement but a restriction.
> 
> It is the essential reason why NAT is not acceptable.
> 
>                                                         Masataka Ohta