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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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► Navigate <strong>and</strong> manipulate the directory structure.<br />

► List files available for transfer.<br />

► Define the transfer mode, transfer type, <strong>and</strong> data structure.<br />

► Transfer data to or from the remote host.<br />

► Disconnect from the remote host.<br />

Connecting to a remote host<br />

To execute a file transfer, the user begins by logging in to the remote host. This<br />

is only the primary method of implementing security within the FTP model.<br />

Additional security can be provided using SSL <strong>and</strong> TLS, which we discuss later<br />

in this chapter (see 14.1.9, “Securing FTP sessions” on page 527). Conversely,<br />

this authentication can be bypassed using anonymous FTP (see 14.1.7,<br />

“Anonymous FTP” on page 525).<br />

There are four comm<strong>and</strong>s that are used:<br />

open Selects the remote host <strong>and</strong> initiates the login session.<br />

user Identifies the remote user ID.<br />

pass Authenticates the user.<br />

site Sends information to the foreign host that is used to provide<br />

services specific to that host.<br />

Navigating the directory structure<br />

After a user has been authenticated <strong>and</strong> logged on to the server, that user can<br />

navigate through the directory structure of the remote host in order to locate the<br />

file desired for retrieval, or locate the directory into which a local file will be<br />

transferred. The user can also navigate the directory structure of the client’s host.<br />

After the correct local <strong>and</strong> remote directories have been accessed, users can<br />

display the contents of the remote directory. The subcomm<strong>and</strong>s that perform<br />

these functions are as follows:<br />

cd Changes the directory on the remote host: A path name can be<br />

specified, but must conform to the directory structure of the<br />

remote host. In most implementations, cd .. will move one<br />

directory up within the directory structure.<br />

lcd Changes the directory on the local host. Similar to the cd<br />

comm<strong>and</strong>, a path name can be specified but must conform to the<br />

directory structure of the local host.<br />

516 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong>

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