I have ftped between two i's in a room many many times, no problem.  I have an i over in germany I needed to ftp to, and sometimes I could do it and some times I could not. Both machines are on V7R1, so that wasn't the issue.

I knew it had to do with "passive" (actually extended passive), and while sendpasv will toggle passive on and off, it does not toggle extended passive, that command is sendepsv  and as soon as I turned off extended passive, the two machines talked to each other like two women gossiping.

So I present this in case you have had issues using the FTP command on the i in that "sometimes it will put or get and sometimes not". I knew I was connected because I could set the remote directory, etc. but as soon as I would do a put, it would enter "extended passive mode" and well.