Access to ftp server seems random / iptable errors

Posted on 2009-04-22
Last Modified: 2013-12-02
I have a local ftp server (Freecom FSG-3) running on Linux 2.6 based on Snapgear. I offer users access to images on the local ftp server (anonymous login) through a html page on a non-local webserver. When I browse to the webpage in Firefox 3.0.8, some 8 thumbnails (instead of 38) are randomly shown. I get a lot of error messages (see attachment) on iptables (also randomly). When I click all massages away, I am able to manually show each thumbnail. I can also access the real image by clicking on the thumbnail.
When I browse with Internet Explorer 7.0.6, I do not see any thumbnail. Choosing show picture doesn't help. Clicking on a non-existing thumbnail returns the error "Internet Explorer cannot display the webpage". "Enable FTP folder view" checked gives the same result. If I uncheck "use passive FTP" I get a login window when clicking on a non-existing thumbnail. No matter what I fill in, I don't get access to the image.
I tried to access the ftp files locally and using an unprotected wireless access point nearby: no difference...
Question by:LDantuma
    LVL 16

    Accepted Solution

    If I understand correctly you have on some web server a HTML page that contains images such as:
    <img src="ftp://...

    I would say that this is a very wrong way to be doing things. Clients may have problems connecting to the ftp - ftp protocol may be blocked by corporate firewalls,  web browsers may have issues as you are experiencing etc.

    Additionally the ftp server may limit the number of connections (usually more strict than http server). This could be a problem because when parsing a page the browser opens a lot of new connections - for each image a new connection.

    Author Comment

    I see. What I want is to show a thumbnail sheet to people (from a webserver), to get access to my images (on my ftp server). Indeed using "<img src="ftp://....".
    What you're saying is that using a ftp server is wrong anyway, anyhow. Correct?
    Is the only way putting the images on a webserver? Or is there an other way? I am hesitant using my FSG as a webserver, because I need a DNS-sevice and I think it is less secure.
    LVL 16

    Expert Comment

    I'm not saying that it's forbiden. Just not very common and people might not see it properly (depending on browsers, their network firewalls etc.).

    There are some solutions:
    1. Copy the images on the server. This can be done with an automated script (cron job).
    2. Create a (php or similar) script that forwards the image
    For example you could call a script like:
    The script would connect to ftp server and returns the contents of the image.

    Personally I would copy at least the thumbnails to the web server.

    Author Comment

    I fully understand. I'm not very good at programming in php, so I opted to use the web server function of my FSG. It's online and working perfectly.
    As far as security is concerned, I found no difference between ftp and http, except the fact that it doesn't matter how I protect the folder I give access to. With ftp I have to specifically give anonymous access, and the other folders are secure. With http it doesn't matter if the folder is username/password protected. Mmm, I guess I do not have a choice if I do not want to program in php.

    Author Comment

    By the way, the error messages mentioning target problem were due to the fact that the html-page directed to thumbnails written with lower case. So the thumbnails were not found.
    I still do not understand why Firefox works better with ftp (showing me at least some thumbnails) and IE not at all.

    Author Closing Comment

    The question of different behavior in IE opposed to Firefox was not answered. Blaz did convince me that I had to use a webserver (al teast for thumbnails). It worked perfectly.

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