CIT 324
_______________________________________________________________________________
INTRODUCTION
Network Administration was never a so easy subject before the 21st century, even though networking is going to be much complex nowadays. It has become easier and possible due to the third-party tools available in the market. But, on the other hand, at the same time, it is also not so simple. Of course, it needs a lot of effort in this regard.
The present era is no doubt, a time of networks spread out like mobile networks, WAN, ATM, etc. Whereas this facilitates human life since the same facility is also creating complexity like a puzzle in a game. Networks are changing the computing paradigm from "number crunching” to communication networks the forests of domains to cloud computing and information highways linking databases.
1. Design, install and evaluate network
2. Deploy and maintain computer hardware (Server, desktop, printers, routers, switches, firewalls, phones, PDA's) and software (application deployment, security updates, and patches) that comprises a computer network.
3. Ensure that the network connectivity throughout a company's LAN/WAN
infrastructure is on par with technical considerations at the network level of an organization's hierarchy.
4. Perform and manage regular backups
5. Provide technical documentation and perform audits
6. Manage and troubleshoot network
7. Security management and virus prevention
Network:
A network is known as a connection of two or more inter-linked computers for the purposes of exchanging data and sharing resources.
“A combination of computer hardware, cabling, network devices, and computer software used together to allow computers to communicate with each other.”
Uses of Computer Network
With the availability and power of today's personal computers, networks increase efficiency and reduce costs. Computer networks achieve these goals in three primary ways:
1 NETWORK ADMINISTRATION
• Sharing information (or data)
• Sharing hardware and software
• Centralizing administration and support
More specifically, computers that are part of a network can share:
• Documents (memos, spreadsheets, invoices, and so on).
• E-mail messages.
• Word-processing software.
• Project-tracking software.
• Illustrations, photographs, videos, and audio files.
• Live audio and video broadcasts.
• Printers.
• Fax machines.
• Modems.
• CD-ROM drives and other removable drives, such as Zip and Jaz drives.
• Hard drives.
The networks for companies may vary according to the size and requirements of a company. As far as their types are concerned they can be of several kinds like LAN, WAN, etc. Some companies may be in need of a network just for internet use, others may require networking for data sharing and some can go farther in this direction needing both at a time with some limitations to the users to secure their resources and restricting others from accessing irrelevant data, etc.
1.1 Networks for Companies
Small Office Network A small office network has the following characteristics:
• Few network segments (for example, one segment on each floor or wing of a building).
• A closed network with no connections to or from another network such as the Internet.
• Support for the IP protocol.
ETWORK ADMINISTRATION
Page 2
Medium-Size Office Network A medium-size office network has the following characteristics:
• Several LAN segments with a backbone (for example, one segment on each floor or wing of a building).
• Dial-up connections for users who connect from home or while traveling.
• Internet connections.
A medium-size office network typically uses a few different types of network media. The different office segments can use 10-megabit-per-second (Mbps) Ethernet or token ring networks, but the backbone network that is used to connect to the different networks and host servers can use 100-Mbps Ethernet, Fiber Distributed Data Interface (FDDI), or other types of networks.
Corporate Network
A typical corporate network has the following characteristics:
• Many LAN segments with a backbone (for example, one segment on each floor or wing of several buildings).
• More than one network protocol.
• Areas configured with Open Shortest Path First (OSPF).
• Dial-up connections for users who connect from home or while traveling.
• Leased-line connections to branch offices.
• Demand-dial connections to branch offices.
• Internet connections.
A corporate network typically uses different types of network media. The different office segments can use 10- megabit-per-second (Mbps) Ethernet or token ring networks, but the backbone network that is used to connect to the different networks and host servers is usually made up of 100-Mbps Ethernet or Fiber Distributed Data Interface (FDDI). Connections to external networks (the Internet) are over leased lines or packet-switched services such as Frame Relay. Connections to branch offices are over either switched media (ISDN or analog modems),
TWORK ADMINISTRATION
Page 3
dedicated media (leased lines or Frame Relay), or the Internet.
Tunneling protocol can be used to connect the branch offices to the corporate network over the Internet, as shown by Router 10 and Network G. This corporate network scenario depicts branch office connections that use switched, demand-dial links and dedicated links.
Dial-Up Branch Office Network This scenario describes the configuration of a network for a branch office that is connected through a dial-up link. A typical branch office network has the following characteristics:
• One LAN segment.
• Demand-dial connections to the corporate office. The following illustration shows an example of a dial-up branch office network. In this scenario, the server running Routing and Remote Access must be configured with a network adapter for the media that is used in the branch office (for example, Ethernet) and an ISDN device or analog modem for connection to the corporate office.
Branch Office over the Internet
Branch offices can be connected through leased or dial-up lines to a corporate network. Using leased or dial-up lines across long distances can be expensive. Routing and Remote Access enables branch offices to connect to the corporate networks by using the Internet. In this scenario, a branch office has a dial-up connection to a local Internet service provider (ISP). The branch office router then makes a secure, encrypted tunnel by using the Point-to-Point Tunneling Protocol (PPTP) across the Internet to the corporate network. This network configuration can result in cost savings because the dial-up line is local instead of long-distance. Note: To establish the tunnel, the branch office router must know the IP address of the corporate network router. age 4
The figure shows an example of a branch office that connects to the corporate network by using the Internet.
In this scenario, the server running Routing and Remote Access acting as a branch office router makes a demand-dial PPTP connection to the server running Routing and Remote Access on the corporate network. The branch office router must be configured with a network adapter for the medium that is used in the branch office (for example, Ethernet) and an ISDN adapter or analog modem for connection to the ISP. Leased line can be used to connect to the ISP, but this scenario discusses only demand-dial connections. The corporate office router must be connected to the Internet by using a leased line.
1.2 Concept of Networking
In the world of computers, networking is the practice of linking two or more computing devices together for the purpose of sharing data and/or resources. Networks are built with a mix of computer hardware and computer software.
Networking hardware
typically refers to equipment facilitating the use of a computer network. Typically, this includes routers, switches, hubs, gateways, access points, network interface cards, Networking cables, network bridges, modems, ISDN adapters, firewalls, and other related hardware. The most common kind of networking hardware today is copper-based Ethernet adapters, helped largely by its standard inclusion on most modern computer systems. Wireless networking has become increasingly popular, however, especially for portable and handheld devices.
Other hardware prevalent within computer networking is datacenter equipment (such as file servers, database servers, and storage areas), network services (such as DNS, DHCP, email, etc) as well as other specific network devices such as content delivery. Other diverse devices that may be considered networking hardware include mobile phones, PDAs, etc.
Networking Software
Network Software is a set of primitives that define the protocol (rules) between two machines. The network software resolves an ambiguity among different types of network.ge 5
making it possible for all the machines in the network to connect and communicate with one another and share information.
Network software is the information, data or programming used to make it possible for computers to communicate or connect to one another. Network software is used to efficiently share information among computers. It encloses the information to be sent in a “package” that contains a “header” and a “trailer”. The header and trailer contain information for the receiving computer, such as the address of that computer and how the information package is coded. Information is transferred between computers as either electrical signals in electric wires, as light signals in fiber-optic cables, or as electromagnetic waves through space.
The concept of computer networking, in fact, is to make a linked and connected medium by which data, communication, and resources can be shared easily. The basic components are computers and networking equipment etc.
For the understanding of the students, it would be worth mentioning that when computers are linked to each other for the purpose of sharing of data and resources, they may be connected via cable or without cable (wireless), they are called part of a network.
1.3 The Network Life Cycle
Modern networks and applications demand improvements in network performance management practices. The Network Life Cycle (NLC) provides a comprehensive framework against which network managers can make critical decisions, whether in moments of an immediate crisis or for long-range planning. The NLC defines a range of needs that require a variety of methodologies and tools for network performance management through Monitoring, Measurement, Assessment and Diagnosis (MMAD). Each phase of the NLC has its own requirements that can typically be met with a judicious selection of tools and assessment solutions. This guide provides critical underpinnings for a successful NLC.
The major phases are:
• Business Case
• Requirements
• Request for Proposals
• Planning
• Staging
• Deployment
• Operation
• Review
Each phase of the typical Network Life Cycle requires some degree of attention to Monitoring, Measurement, Assessment, and Diagnosis (MMAD). NETWORK ADMINISTRATION
Page 6
1.4 Components of Network
In order for a computer to operate on a network, there is a range of different components that are required. A brief overview of the main components are as follows:
Network Cards Network Interface Card (NIC) is also called the LAN adapter. Network cards are required in every machine connected to the network. They allow the signal from the network to be transmitted to the machine – this could be via a fixed cable, infrared or radio waves.
Figure 1.8 Network Cards
NIC works with particular network topology like Ethernet and token ring. The transfer rate of an Ethernet card is from 10 Mbps to 1000 Mbps.
Wireless Access Point
Wireless access points have high-quality antennas for optimal signals. Some manufactures suggest placing the wireless access point at the highest possible location for the best signal
Modems
'Modem' is a made-up word from 'MODulation and DEModulation'. A modem converts the digital data from the computer into a continuous analog waveform that the telephone system is designed to deal with (MODulation) because the telephone system was originally designed for the human voice i.e. continuous signals. The modem also converts the analog signal from the telephone network back into digital data that the computer can understand. (DEModulation). Features of Modem
• Speed: Speed is the rate at which the modem can send data in bits per second (bps).
• Self Testing: Modem can test the digital connection with a computer. It can also test the analog connection with a remote modem
• Voice over Data: Modem provides the facility of voice conversation while data is being transmitted. Both the source and destination modems must have this feature.
• Error Control: Modems use different methods to control errors for transmitted data Standard modems come in two forms. An external box that links to your computer either through a serial or USB port, or an internal modem that is plugged directly to the motherboard inside the computer. Modems connected to the standard telephone line at speeds up to 56 Kilobits per second. Many people still use a 56Kb modem to connect to the internet due to low cost.
A Wi-Fi NIC with an aerial for the signal
An External Modem
Page 7
Wi-Fi Modems In addition to telephone modems, radio has now become very popular as a means of connecting to the internet. The device that allows you to do this is called the Wi-Fi modem
HUB A special type of network device called the hub can be found in small business networks. A hub joins multiple computers (or other network devices) together to form a single network segment. All computers in segment can communicate directly with each other. Essentially, a hub simply receives incoming packets, possibly amplifies the electrical signal, and broadcasts these packets out to all devices on the network - including the one that originally sent the packet. A hub includes a series of ports that each accepts a network cable. Small hubs network four computers. They contain four or sometimes five ports, the fifth port being reserved for "uplink" connections to another hub or similar device. Larger hubs contain eight, 12, 16, and even 24 ports. Star and Tree network topologies use hub. You can also 'daisy chain' hubs to allow even more computers to join the network. However, the problem arises with doing this. Technically speaking, three different types of hubs exist:
• Passive
• Active
• Intelligent
Passive hubs do not amplify the electrical signal of incoming packets before broadcasting them out to the network. Active hubs, on the other hand, do perform this amplification, as does a different type of dedicated network device called a repeater. Some people use the terms concentrator when referring to a passive hub and multiport repeater when referring to an active hub. Intelligent hubs are stackable (built in such a way that multiple units can be placed one on top of the other to conserve space). It also typically includes remote management capabilities via SNMP and virtual LAN (VLAN) support. Hubs remain a very popular device for small networks because of their low cost.
Switches A switch has a number of ports and it stores the addresses of all devices that are directly or indirectly connected to it on each port. As a data packet comes into the switch, its destination address is examined and a direct connection is made between the two machines.
Router A Router is a device that transfers data from one network to another in an intelligent way using similar or different protocols. It has the task of forwarding data packets to their destination by the most efficient route. In order to do this, the router has a microcomputer inside it. This holds a table in memory that contains a list of all the networks it is connected to, along with the latest information on how busy each path in the network is, at that moment. This is called the 'routing table'. When a data packet arrives, the router does the following:-
• • Reads the data packet's destination address
• • Looks up all the paths it has available to get to that address.
• • Checks on how busy each path is at the moment
• • Sends the packet along the least congested (fastest) path. Other tasks the Router can perform:
• Exchange Protocol information across networks
• Filter traffic - useful for preventing hacker attacks for example Routers operate at the network level of the OSI model
Repeaters
All signals fade as they travel from one place to another. Each type of network cable has a maximum useable length. If you go beyond that length, the signal will be too weak to be useful. Of course, computers on a real network can easily be more than 200 meters apart. Therefore the network cable is split up into segments. Each segment is less than the maximum length allowed. Joining the segments together is a device known as a 'Repeater'.
A Repeater boosts the signal back to its correct level. Here are some typical maximum cable lengths:
• • Copper cable - 100 m
• • Thick Ethernet -500m
• • Thin Ethernet - 185m
Bridges
Bridge does just what you would expect it to do - it joins two networks together so as far as data packets are concerned it looks like one large network A bridge is not as capable as a Router - but it is less expensive. Both networks have to be using the same protocol.
Gateways
There are many different network protocols in use today. For example, the large internet company called AOL has its own special email protocol. If your computer does not use the AOL protocol (and the chances are it won't). Then how do you get an email to your friend on the AOL network? The answer is A gateway. the gateway converts the data passing between dissimilar networks so that each side can communicate with each other. i.e converts data into the correct network protocol.
The gateway is a mixture of hardware components and software. This is unlike a standard 'Bridge' which simply joins two networks together that share the same protocol. Filters
Not all data packets are equal. Some are more equal than others. If your network is to be kept secure it is often essential that some filtering takes place. For example, some staff wishes to work from home with their laptops and they need to access files from within the company network. In this case, a filter would be set up that accepts data packets coming from that particular laptop. Other filtering rules would block unwanted packets from trying to come in. Just like Gateways, a Filter can be a mix
Note that a filter can also prevent data packets from leaving the company network. For example, a rule could be set up that only allows an authorized server within the network to send data outside the local network. A filter is an essential component of a 'Firewall'.
1.5 Types of Computers in Networks
Terminals/Node
Every computer that is part of a computer network is called a terminal or node. The users using different terminals can share information and send or received data from one terminal to another. Clients: Which use but do not provide network resources
Peers: Which both use and provide network resources
Workstation: This is a personal computer that runs an application or utility software and uses data that is stored locally or provided by a network server to which it is connected by a cable or media. Workstations are also known as clients.
Servers Server is a network computer from which workstations (clients) access and share files, printers, communications, and other services. Servers can be dedicated to a single service, such as file servers, print servers, application servers, Web servers, and so on. Servers can also be the software that performs, controls, or coordinates a service or resource. Servers Several types of servers can exist on a network, each one performing a different task for the network and its workstations. A server is usually thought of as a computer, but a server is actually the software that performs, controls, or coordinates a service or resource. One computer can physically house many different software servers. To network clients, each server can appear to be a completely separate device, when that is not usually the case. The table below lists the most common types of servers that are implemented on a network. ADMINISTRATION
Server Type Description
File server Stores network users' data files. Files are simple to find and easily be shared. User computers can be switched off without any problem of a file becoming unavailable. Data can be easily backed up
Print server Manages the printers that are connected to the network and the printing of
user documents on the network printers
Communications server
Handles many common communications functions for the network, such as email, fax, or Internet services, For example, The email server will provide all the usual facilities such as address books, spam filtering and so on
Application server Shares network-enabled versions of common application software and
eliminates the need for software to be installed on each workstation
Database server Manages a common database for the network, handling all data storage,
database management, and requests for data Advantages:
• All data is available from anywhere in the network
• A specially designed computer can be selected to run the database e.g lots of memory
• The database is easily backed up
Internet Proxy server
The Internet Proxy server stores a local copy of often-used web pages to speed up access and to reduce bandwidth consumption
Intranet server Many companies run their own private internal web services. This is called an
Intranet and is run from the Intranet server.
Proxy Server
A 'Proxy' is another word for 'Substitute'. This machine has two main tasks:
• Supply authorized internal users with web pages
• Supply external users with authorized information and services Quite often staff tend to use the same web sites over and over again. So to speed up access and reduce bandwidth costs, the Proxy server will keep a local copy of the web pages and serve these to the user instead. Of course, rules running on the proxy server will determine how often these local pages need to be updated. The proxy server also acts as a filter:
• Prevents unauthorized users from accessing external networks such as the internet
• Prevents unauthorized web sites to be accessed (stops time-wasting!)
• It provides a web service to external clients but does not allow them through to the internal network itself. For example, a bank web site would be running a proxy service In a way, the proxy server is the outward-facing aspect of the company linked to the internet.
Communication Media
The path through which data is transmitted from one or several senders (or transmitters) to one or several receivers is called communication channel, communication media or transmission media. A channel has a certain capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second. There are two types of transmission media
• Physical/Bounded/Guided Transmission Media
• Wireless/Unbounded/Unguided Transmission Media
Physical/Bounded/Guided Transmission Media Communication devices are directly connected with each other by using some physical media like cable. Some examples are:
Coaxial Cable A coaxial cable consists of a copper wire core covered by insulating material. The insulated copper wire is covered with a copper mesh. The mesh protects the cable from electromagnetic waves. The two conductors usually carry equal currents in opposite directions. You may have seen this type of configuration on cable TV hookups but this is more rarely the case now in computer networks. It is used for long-distance telephone lines and local area networks. It has a data transfer rate of 10 Mbps.
Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable. The two types of coaxial Thin coaxial cable is also referred to as thinnet. 10Base2 refers to the specifications for thin coaxial cable carrying Ethernet signals. The 2 refers to the approximate maximum segment length being 200 meters. In actual fact the maximum segment length is 185 meters. Thin coaxial cable has been popular in LAN linear bus topology Thick coaxial cable is also referred to as thicknet. 10Base5 refers to the specifications for thick coaxial cable carrying Ethernet signals. The 5 refers to the maximum segment length being 500 meters. Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor. This makes thick coaxial a great choice when running longer lengths in a linear bus network.
The most common type of connector used with coaxial cables is the Bayonne-Neill- Concelman (BNC) connector. Different types of adapters are available for BNC connectors, including a T-connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network.
Wire Pair The Most commonly used communication media is wire pair and is made of copper. The pair of wires are twisted together. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot. It is used in local telephone systems and Ethernet networks. It is used for short-distance digital transmission. Twisted pair cabling is often used in data networks for short and medium-length connections because of its relatively lower costs compared to optical fiber and coaxial cable.
Unshielded twisted pair (UTP)
UTP cable is also the most common cable used in computer networking and is generally the best option for local area networks.
A typical subset of these colors (white/blue, blue/white, white/orange, orange/white) shows up in most UTP cables. Wire pairs are selected carefully to minimize crosstalk within a large cable.
Shielded Twisted Pair (STP) Cable Although UTP cable is the least expensive cable, it may be susceptible to radio and electrical frequency interference (it should not be too close to electric motors, fluorescent lights, etc.). If you must place cable in environments with lots of potential interference, or if you must place cable in extremely sensitive environments that may be susceptible to the electrical current in the UTP, shielded twisted pair may be the solution. Shielded cables can also help to extend the maximum distance of the cables.
Shielded twisted pair cable is available in three different configurations:
1. Each pair of wires is individually shielded with foil.
2. There is a foil or braid shield inside the jacket covering all wires (as a group). 3. There is a shield around each individual pair, as well as around the entire group of wires (referred to as double shield twisted pair).
Table 1.2 Ethernet Twisted Pair Cable Identification and Use
Type Speed Detailed Information
Cat. 5 10/100/1000MbE*
Category 5 cable is a currently outdated standard that provides support for up to 100Mhz operation. It can be used for 10/100 Ethernet without worry, however for longer runs of 1000MbE it is recommended to use Cat. 5e or higher.
Cat. 5e 10/100/1000MbE
Category 5e cable provides support for frequencies up to 100Mhz. Cat. 5e generally provides the best price for performance, however for future proofing Cat. 6 or higher might be a better choice as it usually does not cost much more.
Cat. 6 10/100/1000MbE 10GbE*
Category 6 is defined up to a frequency of 250Mhz. Allowing 10/100/1000 use with up to 100 meter cable length, along with 10GbE over shorter distances. Cat. 6a 10/100/1000MbE 10GbE
Cat. 6a or Augmented Category 6 is defined up to 500Mhz. It allows up to 10GbE with a length up to 100m.
Cat. 7 10/100/1000MbE
10GbE/100GbE(?)
Category 7 is the informal name for "Class F" cabling defined by a different standards body than Cat. 6a and lower. It supports frequencies up to 600Mhz and may support the upcoming 100GbE standard Cat. 7a Unknown Category 7a is an upcoming standard that allows frequencies up to
1000Mhz. Supported Ethernet bandwidths have not been defined.
The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector. A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.
Ethernet crossover cable An Ethernet crossover cable is a type of Ethernet cable used to connect computing devices together directly without a hub where they would normally be connected via a network switch, hub or router, such as directly connecting two personal computers via their network adapters. An Ethernet crossover cable has it's send and receive wires crossed. Unfortunately some devices like cable and DSL modems have their actual Ethernet plugs reversed. This is to allow people to hook up a cable modem to a computer without a special crossover cable. When adding a hub into the mix, the issue can get confusing. Most modern hubs and switches have what is called an uplink port on them. This is the same kind of 'reversed' port that is on a cable or DSL modem.
Fiber Optic Cable Fiber optic cables consist of a center glass core surrounded by several layers of protective materials. It transmits light rather than electronic signals eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference.
Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling is high. There are two common types of fiber cables - single mode and multimode. Multimode cable has a larger diameter; however, both cables provide high bandwidth at high speeds. Single mode can provide more distance, but it is more expensive.
Active Cables
Active cables are copper cables for data transmission that use a silicon chip (semiconductor) to boost the performance of the cable. Without a chip, a cable is considered a 'passive' cable
Today, active cables are used to connect consumer devices such as cameras, gaming consoles and HDTVs, as well as enterprise networks which form the backbone of modern data communication systems.
Wireless/Unbounded/Unguided Transmission Media
In this type of media communication devices communicate with each other through air or space. Some examples are:
Microwave transmission is line of sight transmission. The Transmit station must be in visible contact with the receiver station. This sets a limit on the distance between stations depending on the local geography. Typically the line of sight due to the Earth's curvature is only 50 km to the horizon. Repeater stations must be placed so the data signal can hop, skip and jump across the country.
Satellite Satellites are transponders (space stations) that are set in a geostationary orbit directly over the equator. A transponder is a unit that receives on one frequency and retransmits on another. The geostationary orbit is 36,000 km from the Earth's surface. At this point, the gravitational pull of the Earth and the centrifugal force of Earth’s rotation are balanced and cancel each other out. The uplink is the transmitter of data to the satellite. The downlink is the receiver of data. Uplinks and downlinks are also called Earth stations due to being located on the Earth. The footprint is the "shadow" that the satellite can transmit to. The shadow being the area that can receive the satellite's transmitted signal.
Infra-Red This is a very familiar method of transferring data if you are at all aware of your remote control! The television remote control makes use of an infra-red link. PDA and personal organizers often make use of an infra-red link to synchronize calendars and 'to-do' lists.
Bluetooth
Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances (using short wavelength radio transmissions) from fixed and mobile devices, creating personal area networks (PANs) with high levels of security. Multiple devices can be connected at once due to a synchronization feature. This technology became popular with the application of a hands-free headset and a mobile phone. Now Bluetooth is widely used in devices such as the wireless mouse, keyboard, printer, GPS devices, cell phones, microphones and controllers.
Protocol
Protocols are the rules that define how two or more communication devices will communicate with each other. A 'protocol' is a rather technical word. But it simply means an agreed method of doing something. A 'NETWORK PROTOCOL' is the agreed method of communication to be used within the network. Protocols determine:-
• How the communication channel is established
• How information is transmitted
• How errors are detected and corrected.
• Data sequencing i.e. breaking long message into small blocks /packets of same size.
• Data Routing i.e. finding the most efficient path between source and destination NETWORK ADMINISTRATION
Page 17
before sending data.
• Data Flow
• Error checks of the data packets when they arrive
• Error correction of the data packets
• Data packets received correctly
• How does the receiving machine know that the sending machine has finished sending all of the data
• Data compression
Most widely used network protocols have been agreed and developed by international standards organizations such as the ITU (International Telecommunication Union). Protocols can be used to interconnect PCs to other PCs or networks. The name of these protocols, their acronyms, and the scope of what they interconnect is listed below:
Protocol/Layer Acronym What It Does
Point-to-Point Protocol
PPP Used to connect and manage network communications over a
modem
Transmission Control Protocol/Internet Protocol
TCP/IP The backbone protocol of the Internet
Internetwork Packet IPX/SPX The standard protocol of the Exchange/Sequenced Novell
network operating system's Packet Exchange
NetBIOS Extended User Interface
NetBEUI A Microsoft protocol that is used only by Windows systems
for LANs with no external connections; does not support routing (addressing through a router to other networks)
File Transfer Protocol FTP FTP is a method to transfer files across the Internet using an
FTP client program.
Hypertext Transfer Protocol
HTTP Used to send World Wide Web (WWW) documents, which
are usually encoded in HTML across a network. It provides a standard for Web browsers and servers to communicate.
Network File Services NFS Allows the network node to access network drives as if they
were local drives, files, and data; also performs the file-access and data-retrieval tasks that are requested of the network
Simple Mail Transfer Protocol
SMTP Used to send electronic mail (e-mail) across a network
Telnet Telnet Used to connect and log in and manage a remote host
Point-to-Point Protocol over Ethernet
PPPoE A network protocol for encapsulating Point-to-Point Protocol
(PPP) frames inside Ethernet frames. It is used mainly with DSL services where individual users connect to the DSL modem over Ethernet. e.g., PTCL broadband modems use it for connecting to DSL Internet service.
Simple Network Management Protocol
SNMP SNMP is a standard TCP/IP protocol for network
management. Network administrators use SNMP to monitor network availability and performance, and control devices to help recover from technical issues.
IP - Internet Protocol IP Data travels over an IP-based network in the form of packets.
Each IP packet includes both a header (that specifies source, destination, and other information about the data) and the message data itself. IP works using a system of numeric addresses and sub-networks (subnets). IP also features the companion protocol ICMP. A new version of IP, IPv6, will someday replace the IP system currently in common usage
Internet Protocol version 4
IPv4 Fourth revision in the development of the Internet Protocol
(IP) and it is the first version of the protocol to be widely deployed together with IPv6
IPv6 IPv6 IPv6 is the next generation protocol for Internet Protocol (IP) networking. IPv6 coexists with and will someday replace the current IPv4 standard. The Microsoft Vista, operating system contains built-in support for IPv6
1.6 Network and Network Types
In simple words, a network is two or more computers that have been connected for the purposes of exchanging data and sharing resources. Networked shared resources range from printers, CD-ROMs, and modems to files and hard drives.
More technically, A combination of computer hardware, cabling, network devices, and computer software used together to allow computers to communicate with each other is called a network.
Networks vary in size and scope. Two computers connected with a cable or wirelessly to exchange files while sitting in a room is a network or it can be a very large global Network such as The Internet that allows almost every computer on the planet to communicate with the other computers on the planet. The term enterprise network refers to a network built by one company, one government institution, one school system, or any other entity.
Area Networks Networks can be categorized in several different ways. One approach defines the type of network according to the geographic area it spans. For example Local area network (LAN), Metropolitan Area Network (MAN), Wide Area Network (WAN), The Internet, the world's largest public WAN.
Network Design Computer networks also differ in their design. The two types of high-level network design are called peer-to-peer and client-server.
Client-server networks are much more common in business and peer-to-peer networks much more common in homes. Client Servers provided centralized processing, storage, administration etc. in this system there is a main host machine (normally mini-frame or mainframe). All users can communicate with this machine via terminals or workstations. Whereas peer-to-peer networks are distributed systems in which all computers in the network are likely to act both as uses of computer services and as providers of computer services.
Wired vs Wireless Networking Many of the same network protocols, like TCP/IP, work in both wired and wireless networks. Networks with Ethernet cables predominated in businesses, schools, and homes for several decades. Recently, however, wireless networking alternatives have emerged as the premier technology for building new computer networks.
Homogeneous and Heterogeneous Networks
A network is called homogeneous network in which all servers and clients have the same operating system. Whereas, a network is called heterogeneous network in which all servers and clients uses different operating systems. Heterogeneous networks are made possible by standards conforming hardware and software interfaces used in common by different products by different manufacturers, thus allowing them to communicate to each other. In Heterogeneous Network Operating systems handle different tasks at widely varying performance levels.
Peer to Peer
Peer-to-peer networks involve two or more computers pooling individual resources such as disk drives, CD-ROMs and printers. These shared resources are available to every computer in the network. Each computer acts as both the client and the server which means all the computers on the network are equals, that is where the term peer-to-peer comes from.
Computers in a peer to peer network run the same networking protocols and software. Peer networks are also often situated physically near to each other, typically in homes, small businesses or schools i.e. small local area networks (LANs). Both wired and wireless small networks can be configured as peer to peer environments. Some peer networks, however, utilize the Internet and are geographically dispersed worldwide. Home networks that utilize broadband routers are hybrid peer to peer and client-server environments. The router provides centralized Internet connection sharing, but file, printer and other resource sharing is managed directly between the local computers involved.
Advantages
• All computers share equivalent responsibility for processing data.
• Allow sharing of files, printers and other resources across all of the devices.
• Software applications can be installed on the single computer and shared by every computer in the network.
• They are also cheaper to set up because most desktop operating systems have the software required for the network installed by default.
• On the Internet, peer to peer networks handle a very high volume of file sharing traffic by distributing the load across many computers.
• Because they do not rely exclusively on central servers, P2P networks both scale better and are more resilient than client-server networks in case of failures or traffic bottlenecks.
Disadvantages
• Peer-to-peer networks are typically less secure because security is handled by the individual computers, not on the network as a whole.
• The resources of the computers in the network can become overburdened as they have to support not only the workstation user, but also the requests from network users.
• It is also difficult to provide system wide services because the desktop operating system typically used in this type of network is incapable of hosting the service.
Peer to Peer and Ad Hoc Wi-Fi Networks Wi-Fi wireless networks support so-called ad hoc connections between devices. Ad hoc Wi- Fi networks are pure peer to peer compared to those utilizing wireless routers as an intermediate device.
Client/Server
The client-server model is a pattern of network communication in which clients send requests to servers over a computer network and the servers send back responses. A client-server network involves multiple clients connecting to a single, central server. The file server on a client-server network is a high capacity, high speed computer with a large hard disk capacity. Client-server model works with any size or physical layout of LAN and doesn't tend to slow down with a heavy use. Servers include web servers, ftp servers, application servers, database servers, name servers, mail servers, file servers, print servers, and terminal servers. Most web services are also types of servers. The client-server model can be used on the Internet as well. Examples of client-server systems on the Internet include Web browsers and Web servers, FTP clients and servers, and DNS.
Many home networks utilize client-server systems without even realizing it. Broadband routers, for example, contain DHCP servers that provide IP addresses to the home computers (DHCP clients). Other types of network servers found in home include print servers and backup servers.
Advantages
• In most cases, client–server architecture enables the roles and responsibilities of a computing system to be distributed among several independent computers that are known to each other only through a network. This creates an additional advantage to this architecture: greater ease of maintenance. For example, it is possible to replace, repair, upgrade, or even relocate a server while its clients remain both unaware and unaffected by that change.
• All data is stored on the servers, which generally have far greater security controls than most clients. Servers can better control access and resources, to guarantee that only those clients with the appropriate permissions may access and change data.
• Since data storage is centralized, updates to that data are far easier to administer.
• Developed to allow more users to share access. Disadvantages
• As the number of simultaneous client requests to a given server increases, the server can become overloaded.
• Client–server, should a critical server fail, clients’ requests cannot be fulfilled. Types of Networks by their scope or scale (Area Networks)
• LAN Local Area Network
• MAN Metropolitan Area Network
• WAN Wide Area Network Local area network (LAN)
Local Area Network is the most common type of network. A small business or corporate department may install a LAN that interconnects from two to hundreds of PCs, using permanently installed cabling or perhaps a wireless technology. A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings. In TCP/IP networking, a LAN is often but not always implemented as a single IP subnet.
In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single person or organization. They also tend to use certain connectivity technologies, primarily Ethernet and Token Ring.
LANs are capable of transmitting data at very fast rate. Data transmission speeds of LAN are 1 to 100 megabits [per second. It is much faster than data transmission over a telephone line. LAN can transmit data in a limited distance. There is also a limit on the number of computers that can be attached to the network.
The components used by LANs can be divided into cabling standards, hardware and protocols. Examples of cabling standards used on LANs are:
• Cat 3, 4,5,5e and 6 cables
• Ethernet cabling standards: IEEE 802.3 (10Base5), IEEE 802.3a (10Base2), IEEE 802.3i (10BaseT)
• Unshielded Twisted Pair (UTP)
• Shielded Twisted Pair (STP)
• Connectors: RJ45, BNC etc Examples of hardware devices are:
• Network Interface Cards NICs
• Repeaters
• Ethernet Hubs or multiport repeaters
• Token Ring MultiStation Access Units (MSAUs), Control Access Units (CAUs) and Lobe Access Modules (LAMs)
• Bridges
• B routers
• Routers
• Gateways
• Print servers
• File servers
• Switches
• Examples of LAN protocols are:
• TCP/IP
• Fiber Distributed Data Interchange (FDDI)
• Asynchronous Transfer Mode (ATM)
Metropolitan Area Networks (MANs) Metropolitan Area Networks (MANs) are networks that connect LANs together within a city and its suburbs. A MAN interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network but smaller than the area covered by a wide area network. In some cases MANs may be as small as a group of building but typically covers an area of between 5 to 50 km diameters. The communication links and equipment in MAN are generally owned by either a consortium of users or by a single network provider who sells the service to the users. The main criterion for a MAN is that the connection between LANs is through a local exchange carrier (the local phone company). MAN often acts as a high-speed network to allow sharing of regional resources (similar to a larger LAN). It is also frequently used to provide a shared resource connected to other networks using a link to a WAN. A MAN is typically owned an operated by a single entity
such as a government body or large corporation. The protocols that are used for MANs are quite different from LANs except for ATM which can be used for both under certain conditions. Examples of MAN protocols are:
• X.25 (56kbps)
• Asynchronous Transfer Mode (ATM)
• ISDN (Integrated Services Digital Network)
• Dedicated lines
• xDSL (many different types of Digital Subscriber Lines)
Wide Area Networks (WAN)
It refers to a network that spans a large geographic area, such as a state, province, country, internationally or continents. WANs often connect multiple smaller networks, such as local area networks (LANs) or metropolitan area networks (MANs). A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address. Most WANs are not owned by any one organization but rather exist under collective or distributed ownership and management. A Wide Area Network involves communication through the use of a wide range of different technologies for connectivity over the longer distances. These technologies include Point-to-Point WANs such as Point-to- Point Protocol (PPP) and High-Level Data Link Control (HDLC), Frame Relay, ATM (Asynchronous Transfer Mode) and Sonet (Synchronous Optical Network). The difference between the WAN technologies is based on the switching capabilities they perform and the speed at which sending and receiving bits of information (data) occur.
WANs generally utilize different and much more expensive networking equipment than do LANs. They can be connected through leased lines or satellites. WAN can reach the parts of the world that is not possible with LANs. The speed of WAN depends on the speed provided by the company. Transmission rate of WAN is typically 56kbps to 45 Mbps. WAN is expensive. WAN is not as fast as LAN.
The world's most popular WAN is the Internet which is a network composed of many smaller networks. Some segments of the Internet, like VPN-based extranets, are also WANs in themselves. Many WANs are corporate or research networks that utilize leased lines. A multinational business that interconnects their offices in different countries uses a WAN. For example
In air ticketing system like PIA, many offices can be joined together using WAN. A person can register a ticket from any office in the country. A bank with many branches in the
country can connect its branches through WAN. The customers can use their accounts from any branch.
Other Types of Area Networks
LAN, MAN and WAN were the original and by far the most popular network categories of area networks mentioned, while the others have gradually emerged over many years of technology evolution.
Wireless networks (WLAN, WWAN) A wireless network is basically the same as a LAN or a WAN but there are no wires between hosts and servers. The data is transferred over sets of radio transceivers. These types of networks are beneficial when it is too costly or inconvenient to run the necessary cables. The media access protocols for LANs come from the IEEE. The most common IEEE 802.11 WLANs cover, depending on antennas, ranges from hundreds of meters to a few kilometers. For larger areas, either communications satellites of various types, cellular radio, or wireless local loop (IEEE 802.16) all have advantages and disadvantages.
Wireless Local Area Network is A WLAN is a LAN based on WiFi wireless network technology.
CAN Campus Area Network, Controller Area Network, or sometimes Cluster Area Network Campus Area Network is a network spanning multiple LANs but smaller than a
MAN, such as on a university or local business campus.
(SAN) Storage Area Network, System Area Network, Server Area Network, or sometimes Small Area Network
Storage Area Network - connects servers to data storage devices through a technology like Fibre Channel.
System Area Network - links high-performance computers with high-speed connections in a cluster configuration. Also known as Cluster Area Network.
(PAN) Personal Area Network
(DAN) Desk Area Network
(VLAN) Virtual LAN
In a legacy network, users were assigned to networks based on geography and were limited by physical topologies and distances. A virtual local area network, virtual LAN or VLAN, is a group of hosts with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location. A VLAN has the same attributes as a physical local area network (LAN), but it allows for end stations to be grouped together even if they are not located on the same network switch. LAN membership can be configured through software instead of physically relocating devices or connections. Technologies able to implement VLANs are:
• Asynchronous Transfer Mode (ATM)
• Fiber Distributed Data Interface (FDDI)
• Ethernet
• Fast Ethernet
• Gigabit Ethernet
• 10 Gigabit Ethernet etc
Good For Not Good For Peer Networks (2-10 Users)
File Sharing Printer sharing Email, Tight budgets Easy installation
Security Backup Organization of Data Database Applications Large networks Simple administration Internet/WAN Access Single-Server Network (10-50 Users)
Centralized file services Network printing E-mail Work flow and groupware Login Security Archiving Organizing Data Easy installation Simple Administration Internet/WAN access
Application Serving Distributed Organization Large Organizations
Multiserver Networks (50-250 Users)
Centralized file services Network printing E-mail Work flow and groupware Login Security Application Services Large Databases Internet/WAN access
Tight Budgets Easy installation Organizing Data Simple Administration
Tight Multiserver High-Speed
budgets Backbone Network
Easy installation (250-1000 Users)
Organizing data Speed
Enterprise Network (1000+ Users)
Network printing
Tight Budgets E-mail
Easy Installation Work flow and groupware
Centralized file services Login security
Organizing Data Application Services
Speed Client-Server Database Internet Access
Topology
Physical layout of connected devices in a network is called a topology. It is the geometric arrangement/shape. The shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle in an office, but it would be highly unlikely to find a ring topology there. Network topologies are categorized into the following basic types:
• Bus topology
• Ring topology
• Star topology
• Tree topology
• Mesh topology
More complex networks can be built as hybrids of two or more of the above basic topologies.
Bus Topology Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.
Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernet cabling options many years ago for bus topologies. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.
1. INTRODUCTION TO NETWORK ADMINISTRATION
NETWORK ADMINISTRATION
Certralized File services Network Printing E-mail Work Flow and Groupware Login Security Application Services Client-Server Database Internet/WAN
Star Topology Many campus and office networks use the star topology. A star network features a central connection point called a "hub" that may be a hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet. Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)
Ring Topology
In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network. To implement a ring network, one typically uses FDDI, SONET, or Token Ring technology. Ring topologies are found in some offices.
Tree Topology
Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the “root” of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.
Mesh Topology
Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.
A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.
Network Domains Servers and workstations are classified into domains by the role that they play on the network. Network domains, domain controllers, and the names of the resources in a domain are important things to know
Domain A domain is a collection of hardware and software resources and the user accounts that have access to them. The resources may include multiple servers, printers, CD-ROM drives, RAIDs, and other devices that are attached to the network.
DNS - Domain Name System DNS technology allows hosts on TCP/IP networks (such as Internet Web sites) to be addressed by names. DNS includes a network protocol and a distributed data store for lookup of host names and addresses.
Nslookup nslookup is a troubleshooting tool used to obtain information about Internet servers. As its name suggests, nslookup finds name server information for domains by querying DNS. The command line version nslookup.exe can query DNS servers for IP address (A), mail server (NX) and other DNS records. Wed-based variants of nslookup may support additional lookup and user interface features.
DNS automatically converts the names we type in our Web browser address bar to the IP addresses of Web servers hosting those sites.
IP Lookup - Forward and Reverse Address Lookup Several Internet services and network utilities including DNS support lookup of Internet Protocol (IP) addresses. Forward IP lookup converts a server or domain name to an address. Reverse IP address lookup converts the number to the name.
ipconfig - Windows Command Line Utility ipconfig is a command line utility that allows you to manage the DNS and IP address information of a Microsoft Windows computer.
DNS Server A DNS server is a special type of computer on the Internet used to support the Domain Name System. Numerous DNS servers across the Internet maintain a distributed database of domain names and IP addresses.
DNS Caches and Cache Poisoning A DNS cache is a small database maintained by a computer's operating system. The database contains records of all recently accessed Internet domains.
Internet Domain Extensions Domain extensions on the Internet are often called top level domains (TLDs). Dot-com (.com) is the most commonly used top-level domain extension on the Internet. Many others exist, however. DDNS - Dynamic DNS Unlike DNS that only works with static IP addresses, DDNS works with dynamic IP addresses, such as those assigned by an ISP or other DHCP server.
DNS Poisoning Poisoning a DNS server occurs when hackers alter the DNS records for a specific domain, redirecting unsuspecting users to a different Web site than the authentic one.
Open Systems Interconnection (OSI) Model The OSI model offers a framework for understanding network design concepts. Many popular network technologies today take some design elements from the OSI model. Many entry-level network certification programs also require knowledge of OSI.
The Open Systems Interconnection (OSI) reference model has been an essential element of computer network design since its ratification in 1984. The OSI is an abstract model of how network protocols and equipment should communicate and work together (interoperate). The OSI model is a technology standard maintained by the International Standards Organization (ISO). Although today's technologies do not fully conform to the standard, it remains a useful introduction to the study of network architecture.
The OSI Model Stack The OSI model divides the complex task of computer-to-computer communications, traditionally called internetworking, into a series of stages known as layers. Layers in the OSI model are ordered from lowest level to highest. Together, these layers comprise the OSI stack. The stack contains seven layers in two groups:
Upper layers -
7. application
6. presentation
5. session
Lower layers -
4. transport
3. Network
2. data link
1. physical
Upper Layers of the OSI Model OSI designates the application, presentation, and session stages of the stack as the upper layers. Generally speaking, software in these layers performs application-specific functions like data formatting, encryption, and connection management. Examples of upper layer technologies in the OSI model are HTTP, SSL and NFS.
Lower Layers of the OSI Model The remaining lower layers of the OSI model provide more primitive network-specific functions like routing, addressing, and flow control. Examples of lower layer technologies in the OSI model are TCP, IP, and Ethernet.
Examples: Internet Protocol (IP) corresponds to the Network layer of the OSI model, layer three. TCP and UDP correspond to OSI model layer four, the Transport layer. Lower layers of the OSI model are represented by technologies like Ethernet. Higher layers of the OSI model are represented by application protocols like TCP and UDP.
In the OSI model, data communication starts with the top layer at the sending side, travels down the OSI model stack to the bottom layer, then traveses the network connection to the bottom layer on the receiving side, and up its OSI model stack.
Benefits of the OSI Model By separating the network communications into logical smaller pieces, the OSI model simplifies how network protocols are designed. The OSI model was designed to ensure different types of equipment (such as network adapters, hubs, and routers) would all be compatible even if built by different manufacturers. A product from one network equipment vendor that implements OSI Layer 2 functionality, for example, will be much more likely to interoperate with another vendor's OSI Layer 3 product because both vendors are following the same model.
The OSI model also makes network designs more extensible as new protocols and other network services are generally easier to add to a layered architecture than to a monolithic one.
NETWORK AD
No comments:
Post a Comment