Transcript Meyers_CompTIA_4e_PPT_Ch09x

Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
TCP/IP Applications
Chapter 9
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Objectives
• Describe common Transport and Network
layer protocols
• Explain the power of port numbers
• Define common TCP/IP applications such as
HTTP, HTTPS, Telnet, SSH, e-mail (SMTP, POP3,
and IMAP4), and FTP
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Historical/Conceptual
Transport Layer and Network
Layer Protocols
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Transport Layer and
Network Layer Protocols
• TCP over IP consists of many other things
– HTTP
– DHCP
– POP
– 500 more terms over TCP
– UDP over IP
– ICMP over IP
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
How People Communicate
• Connection-oriented communication
– Acknowledgement between two people beginning
a conversation
– Conduct the communication
– Close the communication
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
How People Communicate (cont’d.)
• Connectionless communication (UDP)
– No opening acknowledge
– Short message is shouted across a room
– No closing
• Session
– Any single communication between computers
– All sessions must begin and end
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Test Specific
TCP
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Transmission Control Protocol (TCP)
• Enables connection-oriented communication
• Most common type of session in a TCP/IP
network
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Three-Way Handshake
Communication Process
• Client sends a SYN (synchronize) packet to the
Web server
• One computer (Server) returns a single SYN,
ACK (synchronize/acknowledge) packet
• Client sends a single ACK packet and requests
that Server begin sending the Web page
• After the Web page is sent, Server sends a FIN
(finished) packet
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Three-Way Handshake
Communication Process (cont’d.)
• Client responds with ACK and sends its own
FIN packet
• Server responds with ACK
• Both parties consider the session closed
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.1 A connection-oriented session starting
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.2 A connection-oriented session ending
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
User Datagram Protocol (UDP)
• Used by very few applications
• Requires much less overhead than TCP
– No start, no acknowledgement, no end
• Example of application using UDP: DHCP
– Each step of a DHCP session sends information
without any confirmation
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.3 DHCP steps
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
NTP/SNTP
• Network Time Protocol (NTP)
• Simple Network Time Protocol (SNTP)
• Both synchronize the clocks of devices on a
network
• Uses port 123
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Trivial File Transfer Protocol (TFTP)
•
•
•
•
•
Uses UDP
Transfers files between computers
Does not have any data protection
Never use it over the Internet
Best use: between computers on the same
LAN
• Uses port 69
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Internet Control Message Protocol
(ICMP)
• Works at layer 3 to deliver connectionless
packets
• Handles issues such as disconnect messages
• Ping is an ICMP application
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
ping
• Sends a single ICMP packet called an echo
request to a specified IP address
– All computers (unless blocked by a firewall)
respond with echo reply
– Responses
• Destination host unreachable
• Request timed out
– Early version had a bug that allowed ‘ping of
death’ to crash the recipient computer
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.4 ping in action
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Internet Group Management Protocol
(IGMP)
• Used for multicasts
– Routers use to determine a group membership
• Multicast
– Uses a small subnet of the Class D range
– Does not assign IP addresses
– Group assigned 224.0.0.0/4 address
– Those who wish to receive multicast must join the
IGMP group
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.5 IGMP in action
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
The Power of Port Numbers
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
The Power of Port Numbers
• Every TCP/IP application requires a server and
a client
• Clearly defined port numbers exist for popular
and well-known applications
• Well-known port numbers from 0 to 1023
reserved for specific applications
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.6 HTTP ACK packet
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.7 Dealing with the incoming packet
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
The Power of Port Numbers (cont’d.)
• The Web client’s source port number is
generated by the Web client computer
• Ephemeral port numbers
– Operating systems assign values 1024 to 5000
– IANA recommends using only ports 49152 to
65535
• Dynamic or private port numbers
– Values 49152 to 65535
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.8 A more complete IP packet
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.9 Returning the packet
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Registered Ports
• 1024 to 49151
• Less-common TCP/IP applications register
their ports with IANA
• Most operating systems avoid registered port
numbers for ephemeral ports
– Dynamic/private ports are used instead
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
0-1023
Well-known port numbers
1024-49151
Registered ports
49152-65535
Dynamic or private ports
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Using Ports in a Session
• Both computers keep track of the status of the
communication
– Session information is held in RAM
– Socket or endpoint: one side’s session information
– Socket pairs or endpoints refer to data each
computer stores about the connection
– Session or connection refers to the connection in
general
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Endpoint Information
• Source and destination for one session
• Many simultaneous sessions
• Use netstat –n to see sessions
– Usually shows many connections
– TCPView for Windows: dynamic
– Net Activity Viewer for Linux
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.10 Two open windows
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.11 TCPView in action
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.12 Net Activity Viewer in action
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Connection Status
• Connection states change continually
• Open port or listening port
– Socket prepared to respond to any IP packets
destined for that socket’s port number
• Every serving application has an open port
• A Web server will have open port 80
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Connection Status (cont’d.)
• netstat –an shows all listening ports on a
computer
• Results of running netstat -an
– Active connections
– Protocol
– Local address
– Foreign address
– State
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Process ID (PID)
• Assigned to every running program on a
computer
– The –o switch with netstat shows the PID
• Used by the OS to track running programs
• Commands to provide program name
– netstat –b (Windows) and ps (Linux)
• Windows Task Manager shows all running
processes
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.13 Process Explorer
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Rules for Determining
Good vs. Bad Communications
• Memorize a bunch of common ports
• Learn how to use netstat
• Learn the ports and processes that normally
run on your operating system
• Research unrecognized processes
• Get rid of bad processes
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Common TCP/IP Applications
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
The World Wide Web
• Web servers
– Store HTML documents
– Latest version: HTML5
• Web browsers request HTML pages from Web
servers and open them
– Can use IP address or text address
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.14 My wireless access point’s Web interface
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.15 HTML5 source code
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Hypertext Transport Protocol (HTTP)
• Underlying protocol of the Web
– Runs by default on TCP port 80
– Places http:// at beginning of Web server address
• A general weakness of HTTP
– Relays commands without reference to any
previous commands
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
HTTP (cont’d.)
• Other technologies that enhance HTTP
– JavaScript/AJAX
– Server-side scripting
– Adobe Flash
– Cookies
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Publishing Web Pages
• A Web server will “host” an HTML document
• Methods
– Self-host
• Install Web server software and acquire a public IP
address
• Time-consuming and challenging
– Host through an Internet Service Provider (ISP)
– Use a Web hosting service company
– Free Web hosting (nothing is free)
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Web Servers and Web Clients
• A Web server delivers Web pages to client
computers
– Listens on port 80 for HTML requests
– Fetches and sends requested HTML pages
• To create a Web server
– Install Web server software
– Connect the computer to the Web
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Web Server Software
• Microsoft Internet Information Services (IIS)
– 20-connection limit on client versions of Windows
– IIS only runs on Server versions of Windows
• Apache HTTP Server
– Used by the majority of UNIX/Linux systems
– Approximately 50 percent of Internet Web servers
– Free
– Add-on GUIs (e.g., Webmin) are available
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.16 IIS in action
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.17 Webmin Apache module
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Web Server Software (cont’d.)
• Web server software market share
– Apache is the most common on the Internet
– nginx ranked second for active sites
– IIS has about 11 percent share
– Google Web Server (GWS)
• Only used by Google servers
– Hundreds of other Web servers primarily for small
personal Web sites
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Web Client Software (Browsers)
• Request and display Web pages
• Many have multiple functions
• Most popular:
– MS Internet Explorer (IE)
– Mozilla Firefox
– Apple Safari
– Opera
– Google Chrome
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Secure Sockets Layer (SSL) and HTTPS
(Hypertext Transfer Protocol over SSL)
• HTTP is not secure
• Requirements for secure Internet applications
– Authentication
– Encryption
– Nonrepudiation
• SSL and HTTPS offer security
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Secure Sockets Layer (SSL)
•
•
•
•
•
•
•
Developed by Netscape
Uses public key to encrypt information
Sends encrypted data over an SSL connection
The receiving end decrypts using a private key
Supported by Web browsers and servers
Many Web sites use SSL for confidential data
Look for HTTPS or a small lock icon in browser
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
HTTP Over SSL (HTTPS)
• Uses TCP port 443
• Being replaced by Transport Layer Security
(TLS)
– Functionally the same with Web pages
– TLS is covered more in Chapter 11
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.18 Secure Web page
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Telnet and SSH
• Telnet allowed dumb terminals to connect to
more than one mainframe
• Run commands as if sitting at the mainframe
• Uses port 23
• Telnet server access requires logon with user
name and password, but has no encryption
• Secure Shell (SSH) replaced Telnet providing
data encryption and authentication
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.19 WANG dumb terminal
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.20 Telnet client
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Telnet/SSH Servers and Clients
• telnetd: oldest Telnet server
• Windows comes with a basic Telnet server
– Disabled by default
• Third-party server example: freeSSHd
• All popular, modern Telnet servers are also
SSH servers
• Third-party Telnet/SSH client example: PuTTY
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.21 freeSSHd
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.22 OS X Telnet
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.23 PuTTY
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Configuring a Telnet/SSH Client
• When configured, you must provide:
– The host name
– A valid login name
– The password
• Open systems provide the password when the
login name is given or require no
login/password
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
SSH and the Death of Telnet
• With SSH, both logins and data transmittals
are encrypted
– Must have permission to access the server
• SSH uses port 22
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Electronic Mail (E-mail)
• Major part of the Internet revolution
– Has streamlined the junk mail industry
– Provides a quick way for people to communicate
– Sends messages and attachments
– Normally offered as a free service by ISPs
• Most e-mail clients have simple text editors
– Many can be configured to use more sophisticated
editors
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
E-mail (cont’d.)
• Incoming messages are stored on the e-mail
server
– Most e-mail clients notify you when new message
arrives, or download automatically
– You manage messages (archive, forward, print,
delete, and more)
– Most e-mail programs delete downloaded
messages from the server
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
E-mail Application-level Protocols
• SMTP
• POP3
• IMAP4
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Simple Mail Transfer Protocol (SMTP)
• Used to send e-mail
• Travels over TCP port 25
• Used by clients to send messages
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Post Office Protocol Version 3 (POP3)
• One of two protocols used to retrieve e-mail
from SMTP servers
• Uses TCP port 110
• POP3 use is declining in favor of IMAP4
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Internet Message Access Protocol
Version 4 (IMAP4)
•
•
•
•
Alternative to POP3
Retrieves e-mail from an e-mail server
Uses TCP port 143
Supports features not supported by POP3
– Search messages by keyword
– Select messages before download
• Supports folders on IMAP4 servers
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Alternatives to SMTP, POP3,
and IMAP4
• Web-based e-mail
– Access your e-mail from anywhere
– Free
– Handy for throw-away accounts
• Proprietary solutions
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.24 Gmail in action
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
E-mail Servers
• The e-mail server market is fragmented
• Sendmail for UNIX/Linux is leader (SMTP only)
– No GUI interface; third-party interfaces (Webmin)
– Controls about 20 percent of e-mail servers
– Must use a POP3 or IMAP server program to
support e-mail clients
• Eudora’s Qpopper sends mail to POP3 e-mail
clients
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.25 Webmin with the sendmail module
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
E-mail Servers (cont’d.)
• Microsoft Exchange Server (both SMTP
and POP3)
– Only runs on Windows
• Mailboxes: holding areas on mail server for
each user’s messages
– Server arranges incoming messages
– Server returns messages with unknown recipient
– Difficult to manage
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.26 Microsoft Exchange Server
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
E-mail Client
• Enables you to send, receive, and organize
e-mail
• Communicates with:
– SMTP server to send
– IMAP or POP3 server to download messages
• Hundreds of e-mail client programs
– Microsoft Outlook
– Mozilla Thunderbird
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.27 Microsoft Outlook
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Configuring an E-mail Client
• Obtain the server’s domain name and your
mailbox user name and password
• Enter the POP3 or IMAP4 server’s domain
name and the SMTP server’s domain name
• Enter the user name and password of the
e-mail account
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.28 Entering server information in Microsoft Outlook
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
File Transfer Protocol (FTP)
•
•
•
•
•
The original Internet file transfer protocol
Faster and more reliable than HTTP
Includes security and data integrity
TCP ports 20 and 21, by default
Anonymous or secured sites
– Some are both
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
FTP Servers
•
•
•
•
•
•
Store files
Accept incoming connections
Verify user names and passwords
Transfer files
Easy to set up
Most versions of Linux/UNIX have built-in FTP
servers; many third-party servers offer better
solution
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.29 FileZilla Server
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
FTP Is Not Very Secure
• Data transfers are not encrypted by default
– Add usernames and passwords to provide some
level of protection
• Determine the number of clients you wish to
support
– Most anonymous FTP sites limit the number of
users to 500
Copyright © 2015 by McGraw-Hill Education. All rights reserved.
Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
FTP Clients
• You can access FTP servers many ways
– Web site
– Command line
– FTP client applications
• Some Web browsers support FTP, but lack
features
• Dedicated FTP clients work best
– FileZilla client; Mozilla FireFTP add-on to Firefox
Copyright © 2015 by McGraw-Hill Education. All rights reserved.
Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.30 FTP in a Web browser
Copyright © 2015 by McGraw-Hill Education. All rights reserved.
Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 9.31 Author’s FireFTP hard at work
Copyright © 2015 by McGraw-Hill Education. All rights reserved.
Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Active versus Passive FTP
• Traditional FTP uses active process
– Clients send an FTP request on TCP port 21
– Server responds on an ephemeral destination port
with TCP port 20 as the source port
• Passive FTP server works with NAT
– Client sends an FTP request on TCP port 21
– Server sends back a random listening port
number; client sends data to that port
Copyright © 2015 by McGraw-Hill Education. All rights reserved.
Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Copyright © 2015 by McGraw-Hill Education. All rights reserved.