NAT etc. (was: Spam Control Considered Harmful)

Sat Nov 1 22:11:25 UTC 1997

> 	Jumping through all those hoops to make NATs work "seamlessly"
> 	is a glittering bauble.  Lots of interesting knots to go untangle
> 	as folks rework and undo one of the basic assumptions behind IP
> 	which is a single, common addressing space.  And its really an
> 	admission of failure.  

> 	Buying into NATs dooms people to live in thier private hells.

Bill's comments are dramatically on point. If you lived through the DECNET
Phase 4 address translators of the day (HEPNET et al), you will recall the
massive splintering of the DECNET world that resulted from a violation of
one simple assumption: predictible end to end connectivity resulting from
a single, semantically consistent address space. Area boundary translators
of the day (now called NATs) are and were at best stopgaps. Many of us who
aggressively eliminated phase 4 from the backbones of the day did so due
to the massive operational headaches resulting from the NAT's violation of
the end to end reachability and least surprises principle. In fact, I
often thought the death of phase 4 was dramatically accelerated by this
very issue. 

Trying to find ways to better automate these translators is just yet
another constraint to the application developer and network operator,
similar to unusual or unexpected proprietary application gateways. 
Eventually, it becomes too costly or complicated. And something else is
put into place.

Looking practically at this problem, many voices have called out loudly
about the issues of developing routers capable of simpling switching the
current and future traffic levels. Now, we hear suggestions of inter-ISP
NATs that must look at every single packet, transform it without error,
regenerate security, routing, transport and checksum information, and do
it all at wire speed. These views are incompatible and irreconcilable.

I would suggest that address renumbering technology is not identically
equal to the protocol conversion problem. Renumbering is a triggered event
whose administration can be automated at any layer of the topology. 
Protocol conversion happens for potentially every packet, all the time. 
Its impact is widespread across all facets of architecture, application
and infrastructure. And I personally have never seen it work seamlessly,
despite multitudes of generations of attempts. Protocol conversion is the
ugly child of the datacom world. Lets not build it into the design of the
Internet by intent.

I believe the end to end argument has driven much of the success and
value of the global Internet. Its worth preserving as an architectural
principle.

Eric Carroll
Tekton Internet Associates