Linux Networking and
Security
Chapter 1
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Networking Fundamentals
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Explain the purposes and development of computer
networking
Identify common types of networking hardware
Describe how networking software operates
Understand when popular networking protocols are used
Define network routing and describe the purpose of
popular routing protocols
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The Development of
Networked Computers
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Connecting computers and related devices in a local
area network (LAN) provides:
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Ability to share information instantly
Automation of data-processing tasks that involve multiple
computer systems
More efficient utilization of network resources
Trends contributing to network capability
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Network capability added to personal computers
Reduced cost of UNIX-based server computers
Explosive Internet growth and accessibility
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Network Types
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Network Types
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Network Types
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Peer-to-peer
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Computers act as both client and server on the network
There is no reliance on a centralized server to provide access to
data and other resources
Compared to a centralized client-server model, peer-to-peer is
decentralized, meaning any host can communicate with any
other host
Linux is thought of as a peer-to-peer operating system
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Network Types
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Creating a Network
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Creating a Network
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Creating a Network
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Networking Technologies
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Ethernet
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Most widely used technology
Varies in transmission speed, or bandwidth
Token-ring
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Uses a token to identify which computer on the network has the
right to transmit data
Each workstation must be connected to a multistation access
unit (MAU)
Not as fast as Ethernet, and may be more expensive
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Networking Technologies
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Fiber Distributed Data Interface (FDDI)
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Arcnet
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Reliable, but slower token-passing technology
Asynchronous Transfer Mode (ATM)
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Reliable, but slower and costlier than Ethernet
high-speed, very reliable and very expensive used for Internet
backbones
Wireless LAN (WLAN)
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No cables used to connect nodes to the network
Data is transmitted via radio signals of infrared
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Networking Technologies
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Networking Technologies
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Cabling a Network
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Cabling a Network
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Unshielded Twisted Pair (UTP)
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made of several pairs of wires encased in plastic
Comes in six categories, with CAT 6 being the highest quality
and speed
UTP is relatively inexpensive, but is susceptible to interference
from other electrical signals
Shielded Twisted Pair (STP)
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Similar to UTP, but includes a metallic shielding around each pair
of wires
Shielding protects from electrical interference, but is more
expensive than equivalent quality UTP
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Cabling a Network
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Fiber-optic
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A specialized solution using light pulses rather than electrical
pulses to transmit data
Extremely fast transmission speeds and is immune to electrical
interference
Most secure system, but most expensive too
Coaxial Cable (coax)
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Was popular, but overtaken by UTP
Used for cable modems
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Choosing Cable
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Choosing transmission media (cable) means making
trade-offs between:
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Cost of physical cable and its installation
Maximum and typical speed
Susceptibility to interference
Expanding the network over time (scalability)
If a legacy system (existing wiring) is present:
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Consider utilization of any existing cable and its ability to handle
present and future network traffic
Consider usage by intended network workstations
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Last Mile Options
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How Data is Transferred
on a Network
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Data is transferred across a network as a series of
electronic or light pulses
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These on/off pulses are interpreted as data, bits and bytes which
are organized into packets
A packet refers to a collection of data with identifying
information for network travel
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Packets are different sizes based on the network type being
used and are no larger than the Maximum Transfer Unit (MTU) of
the network
If more than the MTU must be send, additional packets are used
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How Data is Transferred
on a Network
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Each packet is organized into two parts:
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The payload is the data to be transferred
The header defines how the parts of the network should handle
the data
Ethernet transmits data packages using a system called
contention
Throughput refers to how much payload information can
be transmitted on a network
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Network Topologies
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Network Topologies
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Network Topologies
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Network Topologies
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Connecting Multiple Networks
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Networking Software
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A network-capable operating system is required in order
to use networking hardware
In networking, different tools are required for different
tasks
Networking is built on a host of networking tools and mist
of these tools are protocols
A protocol is a formalized set of rules for communication
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Conceptual Models
of Networking
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Conceptual Models
of Networking
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Conceptual Models
of Networking
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The software used to maintain each protocol is often
called a protocol stack
Transport layer protocols can be:
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Connectionless, or stateless, which sends each packet without
regard to whether any other packet was received by the
destination computer
Connection oriented, or stateful, which maintains information
about which packets have been correctly received by the
destination computer
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The Internet Protocol
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The Internet Protocol
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IP Addressing
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IP works by assigning a unique address to every
computer on the Internet
IP Addressing is a scheme that allows each network
device to have a unique ID number
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An IP address is assigned to each computer network card or
network device
Each address is 32 bits long, made up of four 8-bit numbers
separated by periods (dotted-quad)
Addresses have two parts: a network ID and a host ID
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IP Addressing
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IP Addressing
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Broadcast and Multicast
Addressing
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To transmit data to every device on the network, use the
broadcast address
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A special IP address where the host ID is all 1’s
These types of messages are used chiefly for system
administration purposes
To transmit data to multiple specific hosts, use
multicasting
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Used when data needs to go to a subset of the devices on the
network
True mulitcasting is not supported by the Internet yet, but its use
is expected to increase
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IPv6
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Replacement to current IP version (IPv4) which is rapidly
running out of addresses
IPv6 uses 128 bits per IP address
IPv6 includes these enhancements over IPv4:
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Will make multicasting more workable
Allows dynamic configuration of networks
Allows routers to make more intelligent routing decisions
IPv6 requires more sophistication in the infrastructure
components of the Internet
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Transport Protocols
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Name Services
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Are Application-layer software programs that let a
computer provides names in place of IP addresses, also
called name resolution.
A domain name refers to a collection of computers ,
usually on the same network, that can be accessed
using a common name
The name service used by the Internet is Domain Name
Service (DNS)
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Transmission Control Protocol
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The workhorse of the Internet, in that all of the services
utilized rely on TCP as their transport protocol
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These include HTTP, SMTP, FTP and Telnet
TCP is connection oriented and therefore guarantees
delivery of each data packet
TCP provides application transport services using ports,
which are numbers that are associated with networkcapable applications
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Transmission Control Protocol
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User Datagram Protocol
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UDP provides fast, connectionless service
Provides a similar service to IP, but with addition of port
numbers
Applications that use UDP include name servers and
network management utilities
The UDP header includes four fields:
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Source and destination ports
Message length and checksum
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Application Protocols
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Routing Concepts
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Routing Concepts
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Routing Concepts
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Routers use a routing table and a routing algorithm to
decide where to send packets
Routing tables consist of at least three items:
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Network ID for which a route is being stored
The network interface through which the network ID can be
reached
The IP address of the upstream router that handles the listed
network ID
Routing tables may contain:
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Routing algorithm, or engine, that determines how to
process a packet sent to the router
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Chapter Summary
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Networks allow users to work more efficiently
Client-server technology assumes intelligent systems
Networking hardware sends data over transmission media,
where data collections are called a packets
Network topologies (bus, star, ring) define the physical and
logical layout of a network
Many types of transmission media are available
Modern networks use different layers of software to handle the
different aspects of managing a network
The OSI and Internet models are two important conceptual
layered models of networking
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Chapter Summary
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Networking protocols can be connection oriented (guaranteed
data delivery) or connectionless
IP addressing can be defined with or without using classes, but
always consist of network and host IDs
Fragmentation allows packets with different MTU sizes to be
routed across intermediate networks
IPv6 will provide more addresses and many additional features
(over IPv4) as it is rolled out
Broadcasting and multicasting provide special methods of
sending IP packages to multiple hosts simultaneously
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Chapter Summary
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Name services convert between IP addresses and humanreadable domain names
TCP, UDP and ICMP are Transport-layer protocols
Many application protocols are used as part of network-aware
programs such as Web servers and email servers
Routers move packets between network segments and they
maintain a routing table to identify how to reach various network
IDs
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