Hi
You have to give more info about the location and method of the ftp
connection and what applications you are using.
Jack (MVP-Networking).

I doubt it's to do with using IP address versus name.

I think it's to do with the FTP mode ( active/PORT or PASV ) which your FTP
client is using.

FTP can operate in one of 2 fundamentally different ways: Active (  PORT )
mode, or PASV mode.  This determines how the data connection is built.  (
either from the outside in ( PORT ), or from the inside out (PASV) ) Active
mode can cause problems if you ( the FTP client ) are behind a NAT router or
firewall, because the inbound data connection may be bolcked as
un-solicited.   PASV mode is designed for clients behind a NAT / firewall.

I suspect the method you are using with IP address is connecting using PASV
mode.  The supplied command-line FTP client is poor, and does not support
PASV mode.   It always uses PORT mode.

All 3-rd party FTP programs will support PASV mode.
Get a better one here:

ftp://ftp.gnu.org/old-gnu/emacs/windows/contrib/ftp-for-win32.zip

Do a ? at ths one, and see there are many more commands.
PASV is the one you need.