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RE: end2end? (was: RE: Where NAT disenfranchises the end-user ...)

  • From: Mike Batchelor
  • Date: Fri Sep 07 15:05:32 2001

Hash: SHA1

> On Fri, Sep 07, 2001 at 10:55:49AM -0700, Mike Batchelor wrote:
> > NAT rewrites certain packet data fields (src addr, src port,
> sometimes mac
> > addr).  So does a ordinary router (ttl decrement).  One breaks
> end2end, the
> > other does not.  What is the difference?
> NAT rewrite more than that, try reading
> 95_pp.htm
> In particular, it rewrites addresses _in the data portion of the packet)
> for the following protocols:
> ICMP, FTP, NetBIOS, RealAudio, CuSeeMe, DNS, Netmeeting, H.323, PPTP and
> several others.
> That's what makes it violate the end2end principal, your _data_ is changed
> by NAT.

Well of course, that was my point.  Where do you draw the line?  The packet
as received is not identical to the packet as it was sent, even when NAT is
not involved.  Along the way, various things get modified, the packet is
encapulated, unwrapped, re-encapsulated, TTLs get decremented, ... all
that are necessary and part of the process of getting the packet to its
destination.  NAT just has more necessary things to change.  I'm not
defending NAT, I dislike it as much as the next clueholder, I am just taking
the devil's advocate position for the sake of discussion.

> --
> Leo Bicknell - [email protected]
> Systems Engineer - Internetworking Engineer - CCIE 3440
> Read TMBG List - [email protected],

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