[Tsvwg] Re: [e2e] e2e principle..where??....
David P. Reed
dpreed at reed.com
Sat Jun 2 16:43:28 PDT 2001
At 03:50 PM 6/2/01 -0700, Randy Bush wrote:
> > As long as the intermediaries preserve protocol semantics while changing
> > headers (adding cookies for instance) or perform actions (load balancing)
> > that are transparent to the end points, there should be no violation of
> > principles, correct?
>as long as we are careful when we paint your car pink, change the doors
>and seats, and convert the fuel injection to an su carb, there should be
>no violation of the warranty and you should not care or notice.
>end to end is pretty literal.
To be more specific, tinkering with the content does NOT preserve the
semantics in most cases. Let me be very specific.
HTTP is a protocol that is used for a variety of applications. The vast
majority of those applications involve a "browser" and a "server" of the
sort you expect. However, HTTP is used to support other types of apps
(e.g. RPC calls between clients, such as SOAP & XML-RPC, and remote control
of certain devices). In these other apps, one *cannot assume* that the
endpoint device understands all the potentially rich set of operations that
HTTP understands. So, for example, assuming that the remote endpoint that
is normally a "browser" can always handle cookies is a bad assumption -
using the cookie facility because it "is transparent to the semantics" in
normal browsers may in fact cause a non-browser application to
malfunction. It's the same mistake as assuming that an intermediary on a
telnet connection knows the character set that can be displayed on the
Yet this is exactly the kind of intervention that fraudulently-advertised
transparent middleboxes are promoted for.
WWW Page: http://www.reed.com/dpr.html
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