FTP [26] is one of the most useful and powerful TCP/IP utilities for
the general user. FTP allows users to upload and download files
between local and remote hosts. Anonymous FTP, in particular, is
commonly available at file archive sites to allow users to access
files without having to pre-establish an account at the remote host.
TELNET might, in fact, be used for this purpose but TELNET gives the
user complete access to the remote system; FTP limits the user to
file transfer activities.
The general form of the FTP command is:
ftp [IP_address|host_name]
An FTP session can be initiated in several ways. In the example shown
below, an FTP control connection is initiated to a host (the Defense
Data Network’s Network Information Center) by supplying a host name
with the FTP command; optionally, the host’s IP address in dotted
decimal (numeric) form could be used. If neither host name nor IP
address are supplied in the command line, a connection to a host can
be initiated by typing open host_name or open IP_address once the FTP
application has been started.
The remote host will ask for a username and password. If a bona fide
registered user of this host supplies a valid username and password,
then the user will have access to any files and directories to which
this username has privilege. For anonymous FTP access, the username
anonymous is used. Historically, the password for the anonymous user
(not shown in actual use) has been guest, although most systems today
ask for the user’s Internet e-mail address (and several sites attempt
to verify that packets are coming from that address before allowing
the user to login).
The “help ?” command may be used to obtain a list of FTP commands and
help topics available with your software; although not always shown,
nearly all TCP/IP applications have a help command. An example of the
help for FTP’s type command is shown in the sample dialogue. This
command is very important one, by the way; if transferring a binary
or executable file, be sure to set the type to image (or binary on
some systems).
The dir command provides a directory listing of the files in the
current directory at the remote host; the UNIX ls command may also
usually be used. Note that an FTP data transfer connection is
established for the transfer of the directory information to the
local host. The output from the dir command will show a file listing
that is consistent with the native operating system of the remote
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