Ftp gettting disconnected

All,

Trying to ftp to a remote ftp server.

See following output:

ftp -dv xx.xx.xx.xx
Connected to xx.xx.xx.xx (xx.xx.xx.xx).
220 Microsoft FTP Service
Name (xx.xx.xx.xx:username): ftpuser
---> USER ftpuser
331 Password required for ftpuser.
Password:
---> PASS XXXX
230 User logged in.
---> SYST
215 Windows_NT
Remote system type is Windows_NT.
ftp> passive
Passive mode off.
ftp> ls
---> PORT xx,xx,xx,xx,xx,xx
200 PORT command successful.
---> LIST
125 Data connection already open; Transfer starting.
02-20-12  09:55AM       <DIR>          113129
08-28-12  10:03AM       <DIR>          115058
09-10-12  12:53PM       <DIR>          115143
09-13-12  02:43PM       <DIR>          115265
09-24-12  06:51PM       <DIR>          115334

226 Transfer complete.
ftp> ls
---> PORT xx,xx,xx,xx,xx,xx
421 Service not available, remote server has closed connection

This is from RHEL5.8 using ftp 0.17-37.el5

Every connection is successful, there is a timeout set but does not seem to be affecting this. As soon as we connect we run an ls command which is successful and less than a second later you run the ls command again and getting the message that you have been disconnected from the server.

This happens after any/every data transfer whether it is ls/dir/put/get, you only get a single data transfer and then you are disconnected.

Using HP-UX previously there was no issue, there has been no change to the ftp server, windows desktops can connect and do not get disconnected, i am also getting the same issue with OEL5.5 servers.

This is not a network/firewall issue as all the network settings are the same for every client we use. It is not an issue with active or passive mode as both modes show the exact same symptoms. However testing ftp from the linux client we can connect to every other ftp site without issue both within and external to the firewall and do not get the same error.

Can anyone suggest why this may be happening? Could it be due to the version of ftp we are using?

windows 7 - Command-line FTP function does not work - Super User