Cant honestly see what the problem was...

Passive FTP is a well established mode, and is router/firewall (at the
client) friendly as they only ever make outgoing connections.

The only advantage I can see with this, is that the server side
router/firewall only needs one port forwarded.

Disadvantage?  How do you handle multiple users and data streams with
everything trying to get through one port?  The IETF link didn't work
for me, even after unwrapping it (and removing the >) I get a 404 error.

Mind you, how would you handle simultaneous connections to one port
anyway...    At present, I don't think it's possible without alterations
to everyone's TCP/IP stack?  Unless someone knows better.

As above, what's wrong with Passive (or PASIV) mode?


Dave B

> -----Original Message-----
> From: Angus Robertson - Magenta Systems Ltd 
> [mailto:[EMAIL PROTECTED] 
> Sent: 16 September 2008 18:11
> To:
> Subject: [twsocket] Single port FTP
> We all know of the problems caused by the FTP data connection 
> with NAT routers, firewalls, etc, so it's interesting someone 
> has come up with an RFC proposal that allows the data 
> connection to also run on port 21.  
> ort-04.txt
> Essentially, a second connection is opened to port 21, with a 
> simple logon process to tie it to the initial 21 connection, 
> then the real data sent after a 200 DATA response.  
>    - The control connection ("--1-->") is established.
>      S--1-->C   220 FTP server ready<CRLF>
>      C--1-->S   USER u001<CRLF>
>      S--1-->C   331 Enter password<CRLF>
>      C--1-->S   PASS xyz<CRLF>
>      S--1-->C   230 You are logged in<CRLF>
>      C--1-->S   SPSV<CRLF>
>      S--1-->C   227 Entering single-port mode (xYab1234)<CRLF>
>    - The data connection ("---2->") is established
>      S---2->C   220 FTP server ready<CRLF>
>      C---2->S   SPDT xYab1234<CRLF>
>      S---2->C   200 DATA<CRLF>
>      C--1-->S   RETR contents.txt<CRLF>
>      S--1-->C   150 Transmitting data<CRLF>
>      S---2->C   (Contents of contents.txt)
>    - The server closes the data connection ("---2->")
>      S--1-->C   226 Data transferred<CRLF>
>      ...
> Angus
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