This is a patch to the current ADT (Aminet Download Tool) source code, so
that you can choose to use "passive FTP".

Installation:
- download misc/unix/adt.c from Aminet (currently version 2.6)
- run "patch -p0 < adt-passive.patch"
- compile and install adt as usual
- delete your ~/.adtrc file if you have one
- run adt and pick the new "Passive FTP" mode

Background:

FTP is an old protocol. To recieve a file from an FTP server, an FTP client
like ADT normally has to act as a "server" itself, and offer a port for the
FTP server to "connect back" to.

However, many people get internet connectivity by going through a firewall,
and while firewalls usually let any connections through if they're from
inside the wall connecting to the outside, the reverse is not true. To a
firewall, an FTP server's attempt to "connect back" is an unrequested
intrusion, so it is blocked.

However, there is a way around this. The client can request a "passive"
data connection, where the server opens another port and the client
connects to that for the data connection. The dumb firewalls see this as
yet another outgoing connection from the client, and don't block it. An FTP
server isn't required to offer passive FTP, but most do.

 PERMSSN    UID  GID    PACKED    SIZE  RATIO     CRC       STAMP          NAME
---------- ----------- ------- ------- ------ ---------- ------------ -------------
[generic]                 1468    3193  46.0% -lh5- bc97 May 28  2002 adt-passive.patch
[generic]                  680    1351  50.3% -lh5- f4ad May 28  2002 adt-passive.readme
---------- ----------- ------- ------- ------ ---------- ------------ -------------
 Total         2 files    2148    4544  47.3%            May 28  2002