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  • #2297697

    FTP big file


    by bytj ·

    I have some files, which are often as big as more than 1,000 MB. I need to ftp these files regularly to another company. The first file can be sent successfully and the targeted company can receive it. However, the second file will fail to be sent for some reason. It just stuck there. What may be wrong for this? The two or three files must be sent together by our application instead of separately.


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    • #2672077

      Reply To: FTP big file

      by mshavrov ·

      In reply to FTP big file

      It sounds like your FTP Control Session expires somewhere on the way.

      Usually FTP session consists of 2 separate streams. First, you establish “control” connection on TCP port 21 (it’s your interaction with FTP server). Then, when you start transfering data, FTP protocol opens another TCP session, on TCP port 20 on one side and random TCP port number on client side (“data” connection”). It’s background…

      Now let’s talk about possibilities may happen on these two streams along the way between client and server. Usually Firewalls (security devices), monitor for IDLE sessions. For example, if you have nothing on “TCP session on TCP port 21” for 30 minutes, this session will be terminated by firewall. Every piece of information, transfered in this session will reset “30-minutes timer”.

      And now what can you do to prevent this. All you need to keep your “control” session alive. Simpliest thing you can do – use “hash” command before you start uploading file. What it does, it prints “#” sign for each transfered block of data. This will keep your “control” session alive. Only thing you should be sure, how your application will handle this “additional” traffic.

      Another way is in using something like “download manager” to upload files. But you have to evaluate it. I can’t advice one…

      Good luck,

      Michael Shavrov
      MCSE W2K, Sun SCSA, Security+, CCNP, CCDP, CCSP.

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