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FTP uses the services of TCP.

It needs two TCP connections.

The well-known port 21 is usedfor the control connection

and the well-known

port 20 for the data connection.

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Figure 20-1

FTP

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20.1 Connections: The control connection

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The Data Connection

Uses Servers well-known port 20

1. Client issues a passive open on an ephemeralport, sayx.

2. Client uses PORT command to tell the serverabout the port numberx.

3. Server issues an active open from port 20 to

portx.4. Server creates a child server/ephemeral port

number to serve the client

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Creatingthe data

connection

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Figure 20-4

20.2 Communication

Using the control connection

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NVT

FTP FTP

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Format of NVT ASCII characters

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Format of NVT control characters

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Figure 20-5

Using the data connection

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File Type

ASCII or EBCDIC

Nonprint

TELNET

Image

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Data Structure

File Structure

Record Structure

Page Structure

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Transmission Mode

Stream mode

Block mode

Compressed mode

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20.3 Command processing

Access Commands File Management

Data Formatting

Port defining File transfer

Miscellaneous

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20.4 File transfer

Fi 20 8

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Figure 20-8

Example 1

Fi 20 9

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Figure 20-9Example 2

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USERINTERFACE

20.5

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Solution

%ftp challenger.atc.fhda.edu

Connected to challenger.atc.fhda.edu

220 Server ready

Name:forouzan

Password:xxxxxxx

ftp >ls /usr/user/report

200 OK

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Solution

150 Opening ASCII mode

...........

226 transfer complete

ftp >close

221 Goodbye

ftp >quit

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ANONYMOUS

FTP

20.6

S l i

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Solution

% ftp internic.net

Connected to internic.net

220 Server ready

Name:anonymous

331 Guest login OK, send guestas password

Password:guestftp >pwd

257 /is current directory

S l ti

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ll h ll

Solution

ftp >ls

200 OK

150 Opening ASCII mode

bin

ftp> close221 Goodbye

ftp> quit