FTP-server in passive mode "sort of working"



  • I figured I should try to finally make our public FTP server work also for passive FTP as most of our clients accesing it are using IE or Firefox that defaults to passive.

    We have our FTP server on OPT1 with a NAT forward of a public WAN address to port 21 to the opt1 FTP local address. "FTP helper" seems to work as I don´t even have to tell the FTP server to reply with the external IP for it to work in passive mode. Everything in regards to active FTP are working flawlessly with no problems what so ever. Passive are also working, but only for a certain number of requests and then it stops working. If I use IE I can get between 5 to 75 files and then it times out. Filezilla can get more files due to that the client login again when it times out, but even then the FTP server will not allow it to have more than 10 concurrent logins. So even with Filezilla in passive mode the server will deny any new logins when the number of logings for a single user are exeeded.

    I´m just guessing that there are a lot of open connections making this happen.

    We got about 10000 jpg´s on the FTP server that customers are downloading for their web shops, so a lot of small files. It´s never a problem downloading large files, just many files in passive mode.

    So basically it seems that FTP-helper are working, but not very well in passive mode. Is this a known problem and is there a simple way of fixing this?