Chapter 3:
Network Protocols and
Communications
Introduction to Networks
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Chapter 3
3.1 Rules of Communication
3.2 Network Protocols and Standards
3.3 Moving Data in the Network
3.4 Summary
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The Rules
What is Communication?
Establishing the
Rules
 An identified sender
and receiver
 Agreed upon
method of
communicating
(face-to-face,
telephone, letter,
photograph)
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 Common language
and grammar
 Speed and timing of
delivery
 Confirmation or
acknowledgement
requirements
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Protocol’s duty
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The Rules
Message Encoding
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The Rules
Message Formatting and Encapsulation
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The Rules
Message Size
 Segmenting
MSS – maximum segment size
 Multiplexing
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The Rules
Message Timing
 Access Method
Full duplex
Half duplex
 Flow Control
 Response Timeout
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The Rules
Message Delivery Options
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Protocols
Rules that Govern Communications
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Protocols
Network Protocols
 How the message is formatted or structured
 The process by which networking devices share information
about pathways with other networks
 How and when error and system messages are passed
between devices
 The setup and termination of data transfer sessions
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Protocols
Interaction of Protocols
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Protocol Suites
Protocol Suites and Industry Standards
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Protocol Suites
Creation of Internet, Development of TCP/IP
http://cisco.edu.mn/CCNA_R&S_(Introduction_to_Networking
)/course/module3/index.html#3.2.2.2
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Protocol Suites
TCP/IP Protocol Suite and Communication
http://cisco.edu.mn/CCNA_R&S_(Introduction_to_Network
ing)/course/module3/index.html#3.2.2.3
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Exercise
 http://cisco.edu.mn/CCNA_R&S_(Introduction_to_Networking
)/course/module3/index.html#3.2.2.4
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Network Protocols and Standards
Standards Organizations
• The Internet Society (ISOC)
• The Internet Architecture
Board (IAB)
• The Internet Engineering
Task Force (IETF)
• Institute of Electrical and
Electronics Engineers
(IEEE)
• The International
Organization for Standards
(ISO)
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Standards Organizations
ISOC, IAB, and IETF
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Standards Organizations
IEEE
 38 societies
 130 journals
 1,300 conferences each year
 1,300 standards and projects
 400,000 members
 160 countries
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Standards Organizations
ISO
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Standards Organizations
Other Standards Organization
 The Electronic Industries Alliance (EIA) – 19 inch racks
standarts
 The Telecommunications Industry Association (TIA)- The
International Telecommunications Union – VoIP, satellite
 Telecommunications Standardization Sector (ITU-T) - IPTV,
DSL
 The Internet Corporation for Assigned Names and Numbers
(ICANN) The Internet Assigned Numbers Authority (IANA)
DNS
IP
AS number
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Reference Models
The Benefits of Using a Layered Model
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Reference Models
The OSI Reference Model
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Reference Models
The TCP/IP Protocol Model
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Reference Models
Comparing the OSI and TCP/IP Models
http://cisco.edu.mn/CCNA_R&S_(Introduction_to_Networking)/course/module3/inde
x.html#3.2.4.5
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Data Encapsulation
Communicating the Messages
 Segmenting message benefits
Different conversations can be interleaved
Increased reliability of network communications
 Segmenting message disadvantage
Increased level of complexity
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Data Encapsulation
Protocol Data Units (PDUs)
 Data
 Segment
 Packet
 Frame
 Bits
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Data Encapsulation
Encapsulation
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Data Encapsulation
De-encapsulation
http://cisco.edu.mn/CCNA_R&S_(Introduction_to_Networking)/
course/module3/index.html#3.3.1.5
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Moving Data in the Network
Accessing Local Resources
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Accessing Local Resources
Communicating with Device / Same Network
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Accessing Local Resources
MAC and IP Addresses
R1
192.168.1.1
11-11-11-11-11-11
ARP
Request
PC1
192.168.1.110
AA-AA-AA-AA-AA-AA
S1
R1
PC2
192.168.1.111
BB-BB-BB-BB-BB-BB
FTP Server
192.168.1.9
CC-CC-CC-CC-CC-CC
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Accessing Remote Resources
Default Gateway
PC 1
192.168.1.110
AA-AA-AA-AA-AA-AA
R2
172.16.1.99
22-22-22-22-22-22
R1
192.168.1.1
11-11-11-11-11-11
Web Server
172.16.1.99
AB-CD-EF-12-34-56
PC 2
192.168.1.111
BB-BB-BB-BB-BB-BB
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FTP Server
192.168.1.9
CC-CC-CC-CC-CC-CC
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Accessing Remote Resources
Communicating Device / Remote Network
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Accessing Remote Resources
Using Wireshark to View Network Traffic
http://cisco.edu.mn/CCNA_R&S_(Introduction_to_Networking)/course/files/3.3.3.4%20L
ab%20-%20Using%20Wireshark%20to%20View%20Network%20Traffic.pdf 35
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Password phrase
“My favorite spy is James Bond 007.” = MfsiJB007.
“It was the best of times, it was the worst of times.” = Iwtbotiwtwot.
“Fly me to the moon. And let me play among the stars.” = FmttmAlmpats
 To increase the security of passwords, the following Cisco
IOS commands should be utilized:
Enforce minimum password length: security passwords minlength.
Disable unattended connections: exec-timeout.
Encrypt config file passwords: service password-encryption.
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Enforce Minimum Password Lengths
 Make passwords lengthy.
IOS 12.3 and later passwords can be 0 to 16 characters in length.
The best practice is to have a minimum of 10 characters.
 To enforce the minimum length use the global command:
security passwords min-length length
 The command affects all “new” router passwords.
Existing router passwords are unaffected.
 Any attempt to create a new password that is less than the
specified length fails and results in an “Password too short”
error message.
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Disable Unattended Connections
 By default, an administrative interface stays active and logged in
for 10 minutes after the last session activity.
After that, the interface times out and logs out of the session.
 The timer can be adjusted using the exec-timeout command
in line configuration mode for each of the line types that are used.
exec-timeout minutes seconds
Note:
exec-timeout 0 0 means that there will be no timeout and the
session will stay active for an unlimited time.
Great for Labs …
Bad in production networks!
Never set the value to 0!
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Disable Unattended Connections
 Default time is 10 minutes.
 Terminates an unattended connection (console or vty).
 Provides additional level of security if an administrator walks away
from an active console session.
Router(config-line)#
exec-timeout minutes [seconds]
To terminate an unattended console connection after 3 minutes and 30
seconds:
Sudbury(config)# line console 0
Sudbury(config-line)# exec-timeout 3 30
To disable the exec process on the line:
Sudbury(config)# line aux 0
Sudbury(config-line)# no exec-timeout
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Encrypt All Passwords
• Encrypt all passwords in the router configuration file.
Router(config)#
service password-encryption
R1(config)# service password-encryption
R1(config)# exit
R1# show running-config
enable password 7 06020026144A061E
!
line con 0
password 7 094F471A1A0A
login
!
line aux 0
password 7 01100F175804575D72
login
line vty 0 4
password 7 03095A0F034F38435B49150A1819
login
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Securing Local Database Passwords
 Secure the local database passwords.
Traditional user configuration with plaintext password.
username name password {[0] password | 7 hidden-password}
Use MD5 hashing for strong password protection.
More secure than the type 7 encryption.
username name secret {[0] password | encrypted-secret}
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Network Protocols and Communications
Summary
In this chapter, you learned:
 Data networks are systems of end devices, intermediary
devices, and the media connecting the devices. For
communication to occur, these devices must know how to
communicate.
 These devices must comply with communication rules and
protocols. TCP/IP is an example of a protocol suite.
 Most protocols are created by a standards organization such
as the IETF or IEEE.
 The most widely-used networking models are the OSI and
TCP/IP models.
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Network Protocols and Communications
Summary
In this chapter, you learned:
 Data that passes down the stack of the OSI model is
segmented into pieces and encapsulated with addresses and
other labels. The process is reversed as the pieces are deencapsulated and passed up the destination protocol stack.
 The OSI model describes the processes of encoding,
formatting, segmenting, and encapsulating data for
transmission over the network.
 The TCP/IP protocol suite is an open standard protocol that
has been endorsed by the networking industry and ratified, or
approved, by a standards organization.
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Network Protocols and Communications
Summary
In this chapter, you learned:
 The Internet Protocol Suite is a suite of protocols required for
transmitting and receiving information using the Internet.
 Protocol Data Units (PDUs) are named according to the
protocols of the TCP/IP suite: data, segment, packet, frame,
and bits.
 Applying models allows individuals, companies, and trade
associations to analyze current networks and plan the
networks of the future.
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