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Linux Operations and
Administration
Chapter Eight
Network Communications
Objectives
• Identify the important protocols at each layer of the
TCP/IP model
• Describe IP addresses and the difference between
the network and host portions of an IP address
• Convert decimal IP addresses into binary numbers
• Describe the five TCP/IP classes
• Configure your Linux network interface card to
work with TCP/IP, using the command line
• Interact with network devices by using the ping
command
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Introduction to TCP/IP
• Transmission Control Protocol/Internet Protocol
(TCP/IP)
– An internationally accepted set of rules for
connecting computers to the Internet and most other
networks
• Network
– Two or more computers connected with a medium
for the purpose of sharing resources
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Introduction to TCP/IP (cont’d.)
• Two most important protocols in TCP/IP suite:
– Transmission Control Protocol
– Internet Protocol
• Activity 8-1: Researching the TCP/IP Protocol Suite
– Learn about several protocols in the TCP/IP suite
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Working with TCP/IP
• Layers in the TCP/IP model:
– Application layer
• Receives packets from Transport layer
• Opens packets to convert the message back to its
original form
– Transport layer
• Responsible for delivering data from one location to
another on the network
– Internet layer
• Receives packets and then routes them to the correct
destination
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Working with TCP/IP (cont’d.)
• Hardware layers:
– Not part of the TCP/IP protocol suite
– Data Link layer
• Formats data as packets
– Physical layer
• Consists of cables or other connection media
• Deals with data as bits traveling across a network
medium
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Internet Layer
• Sends packets to their specified destinations
• Adds an IP-specific header to the packet
• Header contains information such as:
–
–
–
–
–
–
Source
Destination
Version
Internet header length
Protocol
Other information about the data
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Internet Layer (cont’d.)
Figure 8-1 Information traveling through a network
©Cengage Learning 2013
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Internet Layer (cont’d.)
• Internet Protocol (IP)
– Contains addressing information that enables
packets to be routed
– Two basic functions of IP are addressing and
fragmentation
• Internet Control Message Protocol (ICMP)
– Used to generate IP error messages
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Transport Layer
• Responsible for delivering data from one location to
another on the network
• Transmission Control Protocol (TCP)
– Connection-oriented protocol
– Keeps track of packets and reassembles them into a
single file after they’ve all arrived
– Controls the flow of messages
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Transport Layer (cont’d.)
• User Datagram Protocol (UDP)
– Connectionless protocol
– Doesn’t perform error checking or acknowledge that
messages were sent successfully
• Table 8-1
– Summarizes the differences between TCP and UDP
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Transport Layer (cont’d.)
Table 8-1 Differences between TCP and UDP
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Application Layer
• Sits at the top of the TCP/IP model
• Contains the higher-level protocols used for
network communication in the Transport layer
• Table 8-2
– Describes some important protocols in this layer
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Application Layer (cont’d.)
Table 8-2 Important protocols in the Application layer
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Application Layer (cont’d.)
Figure 8-2 Placement of protocols in the TCP/IP model
© Cengage Learning 2013
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Working with IP Addresses
• IP address
– A unique number that identifies a computer or device
on a TCP/IP network
– Format
• Four numbers separated by periods
• Example: 192.168.75.136
– ifconfig command
• Can be used to view a computer’s IP address and the
current state of all its active network interfaces
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Working with IP Addresses (cont’d.)
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Binary and Decimal Numbering
Systems
• Decimal numbers
– Used in IP addresses
– Have 10 possible digits (0 to 9)
• Binary numbering system
– Uses only two digits (1 and 0)
– Used in computers
• Computers convert decimal IP addresses into
binary numbers
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Binary and Decimal Numbering
Systems (cont’d.)
• Bit (also known as a binary digit)
– Represents a single binary value
• IP addresses
– Decimal numbers divided into four octets
– Each octet is 8 bits
– An IP address has 32 bits
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Binary and Decimal Numbering
Systems (cont’d.)
• Table 8-3
– Lists the powers of two from 0 to 7
• Decimal number 112 converts to binary number
01110000
• Activity 8-2: Converting from Decimal to Binary
– Convert a 32-bit IP address into four 8-bit binary
octet
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Binary and Decimal Numbering
Systems (cont’d.)
Table 8-3 The powers of two
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Network and Host Identifiers
• An IP address is composed of two parts:
– Network ID
• Identifies the network where the host is located
– Host ID
• Identifies a computer or device on a network
• Computers can communicate only with other
computers on the same network
– They must have the same network ID to exchange
information
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Network and Host Identifiers (cont’d.)
• Router
– Used to connect networks and forward packets to
their destinations
– Needed to communicate with computers having
different network IDs
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Subnet Masks
• Subnet mask
– Used to determine which part of an IP address is the
network ID and which part is the host ID
• A subnet mask is 32 bits
• Example
– When a computer reads the IP address
255.255.255.0, it converts the decimal 255 to the
binary 11111111
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Subnet Masks (cont’d.)
Figure 8-3 A subnet mask
© Cengage Learning 2013
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Subnet Masks (cont’d.)
Figure 8-4 Network and host IDs in an IP address
© Cengage Learning 2013
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IP Address Classes
• IP addresses are divided into five classes to
accommodate varying network sizes
– Class A, Class B, and Class C: most common
classes
– Class D and E networks are for multicasting and
experimentation
• Table 8-4
– Describes the different IP address classes
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IP Address Classes (cont’d.)
Table 8-4 IP address classes
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Class A Networks
• Their subnet mask is 255.0.0.0
• The first bit is always 0
• There can be only 127 Class A networks on the
entire Internet
– Allows 16,777,214 hosts per network
• Assigned to ISPs or very large companies
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Class B Networks
• Their subnet mask is 255.255.0.0
• The first two bits are always 10
• Assigned to large organizations
– Such as government agencies, universities, and
typical companies
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Class C Networks
• Their subnet mask is 255.255.255.0
• The first three bits are always 110
• More than 2 million Class C networks are possible
– Each network can have only 254 hosts
• Assigned to small organizations
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Configuring Network Interface Cards
• OpenSUSE includes tools and utilities to configure
many hardware devices
– Such as printers, network cards, modems, etc.
• Linux provides commands such as ifconfig for
configuring a network interface card (NIC)
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Using the ifconfig Command
• ifconfig command is used to:
– View a computer’s IP address and the current state
of all active network interfaces on it
– Configure NICs
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Using the ifconfig Command
• Using the ifconfig command without arguments
displays network settings
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Using the ifconfig Command
(cont’d.)
• Output description
– Link encap—specifies the type of interface
– HWaddr—specifies the hardware address (also
known as the MAC address) of a NIC
– inet addr—specifies the IP address as well as the
broadcast address (Bcast) and the netmask (Mask)
– RX packets—specifies the number of packets
received (RX)
• Also shows the number of errors and dropped packets
and how many packets were too long
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Using the ifconfig Command
(cont’d.)
– TX packets—displays packets transmitted from
the computer over the network
• Shows error information
– Interrupt—displays the computer’s configuration
settings
• If you have only one NIC, it’s labeled eth0
– All other NICs are labeled eth1, eth2, etc.
• The lo represents the loopback adapter with an IP
address of 127.0.0.1
• All devices using TCP/IP require the loopback
address
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Using the ifconfig Command
(cont’d.)
• ifconfig command can be used to configure NIC
with the following syntax:
ifconfig interface IP address netmask options
• netmask refers to the subnet mask you want to
assign to the interface
• Activity 8-3: Using the ifconfig Command
– View and configure TCP/IP settings with the
ifconfig command
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The ping Command
• Uses ICMP to send an Echo Request packet to a
specified network device on the network and waits
for a reply
• Used by administrators in network testing,
measurement, and management
• Example: ping 192.168.0.6
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The ping Command (cont’d.)
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The ping Command (cont’d.)
• Each ping request produces a result, including:
– icmp_seq
– Time to live (ttl)
– Packet request’s round-trip time
• Table 8-5
– Describes the options you can use with the ping
command
• Activity 8-4: Using the ping Command
– Test your TCP/IP configuration with the ping
command
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The ping Command (cont’d.)
Table 8-5 Options used with the ping command
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Summary
• TCP/IP
– A suite of networking protocols
– Three layers: Application, Transport, and Internet
• IP and ICMP: major protocols at Internet layer
– IP contains addressing information
– ICMP is used to generate IP error messages
• TCP and UDP: major protocols at Transport layer
– TCP is a connection-oriented protocol
– UDP is a connectionless protocol
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Summary (cont’d.)
• FTP and HTTP: protocols at Application layer
• IP address
– Two-part (network ID and host ID) unique number
that identifies a device on a TCP/IP network
– Decimal IP addresses are converted into binary
numbers
– IP addresses are divided into classes
• ifconfig command is used to view and modify
TCP/IP configuration settings
• ping command is used in network testing,
measurement, and management
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