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[DeleGate-En] Re: Transparent Proxy
26 Mar 2008 08:50:55 GMT (Yutaka Sato)
The DeleGate Project


I'm reminded of this message from you :)

On 11/17/07(21:14) you "Kevin Richter" <> wrote
in <_A3903@delegate-en.ML_>
 |other proxies like Squid or frox can detect the destination address
 |from the IP header with
 |getsockopt(fd, SOL_IP, SO_ORIGINAL_DST, ... )
 |This is for a transparent proxy mode. Means: The users dont have to
 |change their local configurations in the ftp program, browser,
 |mail program, ...
 |The POP or FTP protocol do not tell you the destination - normally.
 |The only chance would be to change the username to "username@server.."
 |But sometimes the username is "username@mydomain.." and the
 |POP server is Delegate connects to
 |There is no POP server listening. It does not work.

In such case, you should say "" to the
DeleGate for POP proxy.

 |The analyse of the IP header is the only chance to get the real
 |destination IP.
 |Would it be possible for you to implement such transparent proxy
 |mode feature for ftp, pop, imap?

It might be useful as the "virtual hosting" or "reverse proxy" at
server-side rather than as the "transparent proxy" at the client-side,
since there is no way to recognize or utilize the DeleGate as a proxy
from the client-side in the former case.

I supported SO_ORIGINAL_DST in DeleGate/9.8.2-pre19 in which you can
specify as follows:


If the original address is xx.xx.xx.xx:10021, the DeleGate with the
above specification will act as:


You can make offset the port-number as following configurations:

  SERVER=ftp://odst.-         -->  any input to 21
  SERVER=ftp://odst.-:8021    -->  any input to 8021
  SERVER=ftp://odst.-:-10000  -->  100021 to 21
  SERVER=ftp://odst.-:+10000  -->  100021 to 20021

This will work for any application protocols over TCP supported by DeleGate.


I think "Server Name Indication" of extended TLS might also useful for this

  9 9   Yutaka Sato <>
 ( ~ )  National Institute of Advanced Industrial Science and Technology
_<   >_ 1-1-4 Umezono, Tsukuba, Ibaraki, 305-8568 Japan
Do the more with the less -- B. Fuller

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