Re: ftp_append suddenly not working in put_block

[jthompson@xxxxxxxxxxx]

Sender: jthompson@xxxxxxxxxxx






Thanks for your reply - I think you've nailed it.
There have been some changes to the firewall recently, and FTP is hanging
only occassionally.

I've switched to passive mode, and it seems to be working ok - though I'll
need to see it run cleanly for a couple of days to be sure.

I suppose I now run the risk of our client randomly picking a port on our
vendor's server and not getting past their firewall?

Regards,
John

jthompson@xxxxxxxxxxx
Ph (09) 372-5010


|---------+---------------------------->
|         |           Scott Klement    |
|         |           <sk@xxxxxxxxxxxxx|
|         |           com>             |
|         |           Sent by:         |
|         |           owner-ftpapi@xxxx|
|         |           e.ods.net        |
|         |                            |
|         |                            |
|         |           21/09/2004 11:23 |
|         |           AM               |
|         |           Please respond to|
|         |           ftpapi           |
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  |       To:       ftpapi@xxxxxxxxxxxxx                                                                         |
  |       cc:                                                                                                    |
  |       Subject:  Re: ftp_append suddenly not working in put_block                                             |
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Sender: Scott Klement <sk@xxxxxxxxxxxxxxxx>


Hi,

> Suddenly, after a year of sending files to one of our vendors several
times
> every day, it has started hanging.
>
> The procedure I'm calling is ftp_append, and the error is occurring with
> the call to 'accept' in procedure 'put_block'.

Sounds like a firewall issue.  Have you tried changing to passive mode?

The way FTP works...  there is one "control" connection where the commands
are transferred, and another connection is made each time data is
transferred.  I.e., file uploads, downloads, appends, directory listings,
etc go on the "data" connection.

When using standard (not passive) FTP, the client initiates a connection
to the server on port 21 for the "control" connection.  The server
connects back to the client on random ports for the "data" connections.

In passive FTP, the control connection is done the same way.  But, the
data connections go the opposite direction -- the client connects to the
server's random port for each data connection.

The accept() API is used to receive a new connection from the server in
standard mode.  If the server's ability to connect is blocked by a
firewall, it would just hang on that accept() API indefinitely.

Frequently, people will block all incoming connections in their firewall,
and this prevents the server's connection request from getting there.
Passive mode often fixes this problem because it's common for client
machines to be allowed to make any outgoing connections they want to, and
only limit incoming connections -- so, if that's the case in your shop, a
passive connection may do the trick.

If not, you'll have to talk to your network admin about allowing FTP to
work properly from your machine. Hopefully he understands how to
configure the firewall properly for that to happen.
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