Connection timeout on large files

[Brian Cross]

Serv-U 10.3
Using Filezilla, Smart FTP and SLX Sync Client.

Transferring small files works fine, but any files above 1 MB, the
connection times out, requiring a reconnect to finish the transfer, or
disconnects completely.

Also file transfer is extremely slow (have 4MBit symmetrical
connection) and have sustained speeds of 20 to 30 kbps.

Using Passive Mode (as active mode will not work with the SalesLogix
FTP client yet).

Any ideas I can look at?

[FTPServerTools]

Some ftp clients have a so called keep alive signal, you could try
using that.
I know servu can easily handle high speeds. So it is unclear why it is
slow for you. Maybe the server is set to wrok slow. I assume you do
run the latest 10.3 version. I myself do not have problems even if I
download files of several GBytes. But I know some providers clamp ftp
port 21 as well as bittorrent ports, so you may want to try using a
different port number.
You may want to try ftp voyager as well or alternatively flashfxp
(that one has the keep alive signal).