FTPS and timeout after transferring many small files

Having an odd problem. I have the VSFTPD ftp server up and running on a Redhat 5 server. It's configured to encrypt logons via SSL (Verisign), has a large range of ports open for the PASV connections (over a thousand at the moment). Our DNS zone is split (meaning we manage the zone for internal users and we also manage it for the external world separately). Our Cisco firewall has everything NAT'd so I can use the public ip address of the server both internally and externally.

All works fine for the most part. However, I recently tried to download about 200 very small files (500k average). It bombed out at 150 files (50 MB or so).

Cyberduck says "connection forcibly closed by remote host". The server logs indicate a "421 Timeout" (which is odd as it was cranking away just fine when it stopped). No other errors on the server side.

I can happily transfer a 3GB file with no problems. It's only when I try to download large amounts of files that I get th errors. I can't see a limit on number of files anywhere? Anyone have any ideas? I'd like to roll out this server over the weekend but I'm hesitant with this issue?

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Aaron TomoskyConnect With a Mentor Technology ConsultantCommented:
What's your number of connections per user set to? I use filezilla not cyberduck and it defaults to 10 concurrent connections. If it's goin to fast I've gotten the same error. Dropping filezilla down to 5 connections usually works or me, but sometimes I have to go to 1 if the server is configured that way.
timmr72Author Commented:
Thanks for the quick response. The default on Cyberduck is 5 concurrent sessions (min 1, max 9). When set to the detault of 5, it pulls down 46.8 MB each and every time (about 5 to 6 attempts) before "forcibly disconnecting" me. When set to 1, I got 17MB and 2 got me 47MB. If I click the "resume" button, it will pull down another chunk (200 MB total with 268 files).

The VSFTPD server has unlimited connections (unlimited everything actually).

Filezilla worked fine for me earlier, but I have to support every FTP client known to man on every OS available (including a java ftp client that also bombs out around the same place). Frustrating.
Aaron TomoskyTechnology ConsultantCommented:
I wonder if the cisco is cutting you off for some reason. Too many connections from one ip in x time.
timmr72Author Commented:
Thanks for your help. I think you were on the right track. I've had no problems since increasing my maximum threads from one to five on my java ftp client. Filezilla has been perfect (and fast so far). Cyberduck hasn't been great when I have lots of small files (hundreds). Modifying concurrent connections hasn't helped. I think I'll just recommend a different FTP client if they won't be using the browser based java client we provide.

Thanks for the help.
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