FileZilla FTP server works intermediately

I have installed FileZilla FTP server, v .9.34 beta. For the past two weeks since I installed it, I've been having constant problems, it somes works and sometimes doesn't.  It always works internally, on my LAN, but from the internet, it just sometimes works and sometimes it doesn't.
Any thoughts of what it can be?
DanNetwork EngineerAsked:
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is it setup for Active or Passive FTP? How is it connected to the Internet (NAT over a DSL connection, dedicated link, etc)

The FTP connectivity depends a lot on how you set it up, the ports opened, and the internet connection topology.

Best regards.
DanNetwork EngineerAuthor Commented:
I just left the default, which I think is passive.
I have a 50mb always on connection, it's 5mb/sec download. (fiber)
I have a Cisco router and then a firewall behind that.

I have opened up the necessary ports that the filezilla server uses, and created the necessary NAT rules and everything.  The strange thing is that it somestimes works and sometimes it doesn't externally. Internally, it always works, so it leads me to believe it's something with the firwall, perhaps there's a port conflict?
How are clients connecting? Are they using filezilla? Check the active/passive settings on the clients also.
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DanNetwork EngineerAuthor Commented:
Yes, I instructed everyone to use filezilla client and most are set to default, but if that didn't work, I just informed them to use the passive setting, and that has been working fine until it decides not to work.
So sometimes it works fine and sometimes it doesn't, the weiredest thing.
DanNetwork EngineerAuthor Commented:
I worked with the support of my firewall co. and they said that the client is coming on different ports, so i changed the port range on the ftp server to a smaller range and now it's working, so I'm curiuos to see how long it's going to work for.  
O.K, the client SHOULD come in on different ports.

With passive ftp the server will choose a random high port and tell the client to connect to it on that port.  Most FTP servers will allow you specify a range of high ports to use, which it seems you have setup.

If your firewall is not "ftp aware", then you will need add rules to allow the port range you specified and to forward the port range you specify to your ftp server.

Now, if some of your clients are using active ftp, in which case the client picks a random high port and tells the server.  The server then initiates a connection from port 20 to the port the client told it to use.  If their firewall is not setup to allow this, then the transfer will fail.

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DanNetwork EngineerAuthor Commented:
Thanks everyone for your help.  On the FTP server, I had a port range of 100, so now when I changed it to a range of only 20, it seems to be working fine now.
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