Re: [RRG] arguments for map and encap

[Brian E Carpenter <brian.e.carpenter@gmail.com>]

Christian,

On 2008-05-22 07:34, Christian Vogt wrote:
...
> 
> One may even claim that 1-to-1 translation between globally unique
> edge and transit addresses does not break end-to-end semantics (though
> this is clearly a personal opinion).  What is commonly associated with
> "end-to-end semantics" is that the addresses that a packet receiver
> sees are the same as the addresses the packet sender has used.  But
> specifically and architecturally, what advantage does this have?
> (...Other than not confusing protocols that have been build on the
> assumption that addresses do not change in flight.)  Isn't the true
> meaning of end-to-end semantics covered by global host reachability
> and robustness to route changes, as long as there is a working route?

It's true that there has been a historical assumption that "an address
is an address is an address" and that this has become the essential
implement in applying the end-to-end principle (which was written
down in 1984 [Saltzer] and resurrected in RFC 1958). Afaics, the
essential requirement to apply the e2e principle is an identifier
that asserts that a given packet belongs to a given packet stream.
Given that, the end system doesn't care about any aspect of the
network at all. But we can't avoid the fact that the identifier used
by the vast majority of software is the bitstring known as an address
in the socket API. You can do what you like below the transport layer
as long as you deliver that bitstring. In the real world, we can't change
that (which is why NATs are such a mess, of course).

I don't see any realistic way out of the rule of delivering the address
bitwise as sent. You're completely correct that this does not
mathematically require encapsulation (shim6 is a counter-example).

    Brian

[Saltzer] End-To-End Arguments in System Design, J.H. Saltzer,
   D.P.Reed, D.D.Clark, ACM TOCS, Vol 2, Number 4, November 1984, pp
   277-288.


--
to unsubscribe send a message to rrg-request@psg.com with the
word 'unsubscribe' in a single line as the message text body.
archive: <http://psg.com/lists/rrg/> & ftp://psg.com/pub/lists/rrg