[RRG] A Late Response to Questions on Six/One Router

[Christian Vogt <christian.vogt@nomadiclab.com>]

Comrades,

previous discussions around tunneling vs. address rewriting have shown
that some of the concepts of Six/One Router are unclear in the
community.  This is, of course, my fault because the papers that I
have so far published on Six/One Router do not go into sufficient
detail to dispel these unclarities.  I have done my homework now and
would like to point you to the following paper, which motivates and
explains the design of Six/One Router more thoroughly:

http://users.piuha.net/chvogt/pub/2008/vogt-2008-six-one-router-design.pdf

I would like to especially thank Robin Whittle, who has posed a number
of excellent questions that helped me understand what is unclear about
Six/One Router, and thus address these unclarities in the above paper.

Before responding to Robin's question more carefully in a separate
email, let me here just emphasize two main concepts of Six/One Router.
Likely, this will resolve most of the existing vagueness:

- Mapping between edge addresses and the transit addresses from a
  given provider is one-to-one.  This is why no packet encapsulation
  is necessary:  The edge/transit address after rewriting is
  unambiguously determined by the transit/edge address prior to
  rewriting.  This also makes Six/One Router function without
  per-host state, like tunneling, but unlike NAT boxes.

- Six/One Router has two components, which are independent of each
  other even though they both use address rewriting:  The first
  component uses bilateral address rewriting for communications
  between two upgraded edge networks; the second component uses
  unilateral address rewriting on the border of an upgraded edge
  network for communications with a legacy edge network.  Since
  these components are independent, it is possible to replace either
  of them with a corresponding component from tunnel-based
  approaches:  Bilateral address rewriting can be combined with
  proxies for backwards compatibility.  Tunneling can be combined
  with unilateral address rewriting for backwards compatibility.

I will follow up with a more careful response to Robin's previous
questions about Six/One Router.

- Christian



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