On Mon, Nov 29, 2004 at 05:30:10PM -0800, Jan Brittenson scratched on the wall:
>
> The problem with the question is: if the client managed to connect to
> the web server, why does it need to ask for an address? A cgi-bin
> to figure out a local address to send back to the client that's
> already connected to it is somewhat pointless.
It isn't pointless because you're assuming those addresses are the
same, and that's a very bad assumption because of NAT. In fact,
there are several web servers that offer the opposite service-- you
connect, and they say "you came from THIS address." If the client
is behind a NAT box, the reported address may or may not be different
than what your local machine thinks its own address is. In fact, if
you need to register a "client" with a dynamic DNS service or something
like that, an external reverse probe like this is essential to getting
the correct globally-routed address.
I'm not sure what the original poster is trying to do, but I assume
they know what they are doing. I'll make the standard soap-box
speech that network protocol design is very very difficult-- even at
the application layer-- and you should really know what you're doing
if you are trying to roll your own; that includes the standard
warning that unless you are specifically trying to do some type of
NAT discovery system, encoding end-point IP addresses in an
application protocol stream is usually a Bad Idea, not the least of
which is because it is easy for the system to lie.
That said, there are still reasons why you might want to do this,
especially in a NAT environment. It's just too bad they can't use a
standard server like Apache. This could be solved with a dozen line
script that simply returns the CGI env var "SERVER_ADDR". It's also
worth pointing out that this _is_ a standard CGI env var, meaning
somebody somewhere thought it was important enough to provide.
-j
--
Jay A. Kreibich | Comm. Technologies, R&D
email@hidden | Campus IT & Edu. Svcs.
<http://www.uiuc.edu/~jak> | University of Illinois at U/C
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Darwin-dev mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
http://lists.apple.com/mailman/options/darwin-dev/email@hidden
This email sent to email@hidden
