I have a weird problem with iptables seemingly denying FTP traffic from some FTP clients if the transfer rate is too high...
I have an SME7 server acting as server and gateway between a LAN and the internet. I've done a lot of testing with two FTP clients on the LAN attempting to upload a file to an external FTP server:
- FTP client A can upload without problems.
- FTP client B invariably stops uploading after transferring 200 Kb.
Both are attempting to upload the same file to the same server with active FTP. As far as I can glean from iptraf, there are no differences in how client A and B connects to the server.
The iptables logfile shows that when I test with FTP client B, some traffic coming back from the FTP server is blocked by a denylog rule. The iptables setup is the SME7 out-of-the-box setup with no custom templates.
The wierd mystery is that if I set FTP client B to limit its transfer rate, it can upload sucessfully, without being cut off after 200 Kb... However, FTP client A can always upload sucessfully without limiting the transfer rate, so why FTP client B has trouble with iptables when its transfer rate isn't limited is completely beyond my comprehension.
Anyone have any ideas what the cause might be?
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