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Home > Archive > Unix administration > January 2007 > Active FTP PORT command - port number
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Active FTP PORT command - port number
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| allab@sympatico.ca 2007-01-28, 1:27 am |
| Hello All,
The PORT request has a parameter in the form
h1,h2,h3,h4,p1,p2
meaning that the client is listening for connections on TCP port
p1*256+p2 at IP address h1.h2.h3.h4.
Where p1 and p2 numbers are coming from? Are there any ftp
configuration files?
Thanks,
Alona
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| Barry Margolin 2007-01-28, 1:18 pm |
| In article <1169954472.299107.148130@v33g2000cwv.googlegroups.com>,
allab@sympatico.ca wrote:
> Hello All,
>
> The PORT request has a parameter in the form
>
> h1,h2,h3,h4,p1,p2
>
> meaning that the client is listening for connections on TCP port
> p1*256+p2 at IP address h1.h2.h3.h4.
>
> Where p1 and p2 numbers are coming from? Are there any ftp
> configuration files?
The FTP server normally asks the stack to find an unused port number and
bind the socket to it. It will change from connection to connection.
--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***
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| allab@sympatico.ca 2007-01-29, 1:33 am |
| Barry,
The question was regarding PORT command in ACTIVE FTP mode.
In active mode FTP the client connects from a random unprivileged port
(N > 1023) to the FTP server's command port, port 21. Then, the client
starts listening to port N+1 and sends the FTP command PORT N+1 to the
FTP server. The server will then connect back to the client's
specified data port from its local data port, which is port 20.
Where does the number of a random unprivileged port come from?
Thanks,
Alona
On Jan 28, 9:42 am, Barry Margolin <bar...@alum.mit.edu> wrote:
> In article <1169954472.299107.148...@v33g2000cwv.googlegroups.com>,
>
> a...@sympatico.ca wrote:
>
>
>
>
> bind the socket to it. It will change from connection to connection.
>
> --
> Barry Margolin, bar...@alum.mit.edu
> Arlington, MA
> *** PLEASE post questions in newsgroups, not directly to me ***
> *** PLEASE don't copy me on replies, I'll read them in the group ***
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