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Linux Networking and Security

Chapter 1

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Networking Fundamentals

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 ofNetworked Computers

Connecting computers and related devices in a local area network (LAN) provides: 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 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

Peer-to-peer 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

Ethernet Most widely used technology Varies in transmission speed, or bandwidth

Token-ring 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

Fiber Distributed Data Interface (FDDI) Reliable, but slower and costlier than Ethernet

Arcnet Reliable, but slower token-passing technology

Asynchronous Transfer Mode (ATM) high-speed, very reliable and very expensive used for Internet

backbones

Wireless LAN (WLAN) 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

Unshielded Twisted Pair (UTP) 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) 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

Fiber-optic 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) Was popular, but overtaken by UTP Used for cable modems

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Choosing Cable

Choosing transmission media (cable) means making trade-offs between: 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: 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 Transferredon a Network

Data is transferred across a network as a series of electronic or light pulses 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 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 Transferredon a Network

Each packet is organized into two parts: 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

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 Modelsof Networking

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Conceptual Modelsof Networking

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Conceptual Modelsof Networking

The software used to maintain each protocol is often called a protocol stack

Transport layer protocols can be: 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

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 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

To transmit data to every device on the network, use the broadcast address 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 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

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:

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

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

The workhorse of the Internet, in that all of the services utilized rely on TCP as their transport protocol 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 network-capable applications

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Transmission Control Protocol

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User Datagram Protocol

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:

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

Routers use a routing table and a routing algorithm to decide where to send packets

Routing tables consist of at least three items: 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: Routing algorithm, or engine, that determines how to process a

packet sent to the router

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Chapter Summary

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

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

Name services convert between IP addresses and human-readable 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