System Administrator Roles

What is The Role Of the System Administrator?

Q. Can you explain the role of the system administrator?

A. The person who is responsible for setting up and maintaining the system is called as the system administrator. System administrators may be members of an information technology department. Most of the following discussion also applies to network and Windows system admins.

Duties of a system administrator

The duties of a system administrator are wide-ranging, and vary widely from one organization to another. Sysadmins are usually charged with installing, supporting, and maintaining servers or other computer systems, and planning for and responding to service outages and other problems. Other duties may include scripting or light programming, project management for systems-related projects.

The system administrator is responsible for following things:

1. User administration (setup and maintaining account)
2. Maintaining system
3. Verify that peripherals are working properly
4. Quickly arrange repair for hardware in occasion of hardware failure
5. Monitor system performance
6. Create file systems
7. Install software
8. Create a backup and recover policy
9. Monitor network communication
10. Update system as soon as new version of OS and application software comes out
11. Implement the policies for the use of the computer system and network
12. Setup security policies for users. A sysadmin must have a strong grasp of computer security (e.g. firewalls and intrusion detection systems).

What is so special about the system administrator account?

The root account has full (unrestricted) access, so he/she can do anything with system. For example, root can remove critical system files. In addition, there is no way you can recover file except using tape backup.

Many tasks for system administration can be automated using perl or shell scripts. For example:

• Create new users
• Resetting user passwords
• Lock/unlock user accounts
• Monitor server security
• Monitor special services etc

Most important skill to a system administrator

Problem solving, period. This can some time lead into all sorts of constraints and stress. When workstation or server goes down, you are called to solve the problem. You should able to quickly and correctly diagnose the problem. You must figure out what is wrong and how best it can be fixed in small amount of time.

System administrators are not...

• Cookie cutting software engineers.
• Developers.
• It is not usually within your duties to design new applications software.
• But, you must understand the behavior of software in order to deploy it and to troubleshoot problems, and generally should be good at several programming languages used for scripting or automation of routine tasks such as shell, awk, perl, python etc.

Basic Networking definitions

Common networking terms and their definitions:

Networking: A number of computers (2 or more) linked together to share resources.

Network Interface Card: Also known as an Ethernet card, or NIC card. The NIC is probably the most common component of any network. It is the component that provides the connection between a computers internal bus and the network media or cabling.

Hub: A physical device that serves as a central connection point for several network devices. At its simplest level a hub is nothing more than a multi-port repeater. The hub will repeat what it receives on one port to all its other ports.

Routing: A function of the network that involves moving data through a network. Data passes through several network segments using routers that select the path the data takes.

Router: Usually a physical device that connects two networks and allows data to be sent and received between them. A router will determine the best path for the data to take from its source to its destination.

Category 5 RJ-45 cable: Sometimes called CAT-5 cabling. It is the most commonly used type of network cable. It is used to connect the NIC to a hub, router, and various other network devices.

Network Protocols: Computers and devices on a network have to communicate with each other. A protocol is a predefined set of rules that dictate how the computers and devices communicate and exchange data over a network.

TCP/IP: This is a type of network protocol. It combines the Transmission Control Protocol (TCP) and the Internet Protocol (IP). This is the protocol most commonly used in Windows based networks. It is also the standard protocol used for communications over the Internet. It was originally developed by the Department of Defense.

IP Address: This is an address used by the Internet Protocol to identify a computer or device’s location on the network. This number is usually assigned to a computer by the Internet Service Provider (ISP) or by the network administrator.

DHCP: This acronym stands for Dynamic Host Configuration Protocol. It is a protocol used on a TCP/IP network to send the client configuration data, including the IP address, subnet mask, gateway, and DNS configuration, to the computers or clients on the network. It basically automatically provides configuration data to the computers on a TCP/IP network. Using a DCHP configuration save times by eliminating the need to manually configure each computer on the network.

DNS: Acronym that stands for Domain Name Service. It is a service used in TCP/IP networks that translates host names to IP addresses. The largest use of DNS is the Internet itself. ISP’s use what are called DNS servers to translate web addresses to their actual IP or network addresses. For example when www.winbookcorp.com is accessed by a web browser, the DNS server will translate the site name to the actual network address.

Patch Chords Colour Codings

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Network and Computer Systems Administrator

Basic Job Description:

Install, configure, and support an organization's local area network (LAN), wide area network (WAN), and Internet system or a segment of a network system. Maintain network hardware and software. Monitor network to ensure network availability to all system users and perform necessary maintenance to support network availability. May supervise other network support and client server specialists and plan, coordinate, and implement network security measures.

Activities

Interacting With Computers -- Using computers and computer systems (including hardware and software) to program, write software, set up functions, enter data, or process information.

Updating and Using Relevant Knowledge -- Keeping up-to-date technically and applying new knowledge to your job.

Making Decisions and Solving Problems -- Analyzing information and evaluating results to choose the best solution and solve problems.

Getting Information -- Observing, receiving, and otherwise obtaining information from all relevant sources.

Communicating with Supervisors, Peers, or Subordinates -- Providing information to supervisors, co-workers, and subordinates by telephone, in written form, e-mail, or in person.

Identifying Objects, Actions, and Events -- Identifying information by categorizing, estimating, recognizing differences or similarities, and detecting changes in circumstances or events.

Skills

Troubleshooting -- Determining causes of operating errors and deciding what to do about it.

Reading Comprehension -- Understanding written sentences and paragraphs in work related documents.

Active Listening -- Giving full attention to what other people are saying, taking time to understand the points being made, asking questions as appropriate, and not interrupting at inappropriate times.

Active Learning -- Understanding the implications of new information for both current and future problem-solving and decision-making.

Critical Thinking -- Using logic and reasoning to identify the strengths and weaknesses of alternative solutions, conclusions or approaches to problems.

Complex Problem Solving -- Identifying complex problems and reviewing related information to develop and evaluate options and implement solutions.

Service Orientation -- Actively looking for ways to help people.

Equipment Selection -- Determining the kind of tools and equipment needed to do a job.

Coordination -- Adjusting actions in relation to others' actions.

Installation -- Installing equipment, machines, wiring, or programs to meet specifications.

Time Management -- Managing one's own time and the time of others.

Repairing -- Repairing machines or systems using the needed tools.

Technology Design -- Generating or adapting equipment and technology to serve user needs.

Systems Analysis -- Determining how a system should work and how changes in conditions, operations, and the environment will affect outcomes.

Systems Evaluation -- Identifying measures or indicators of system performance and the actions needed to improve or correct performance, relative to the goals of the system.

Instructing -- Teaching others how to do something.

Learning Strategies -- Selecting and using training/instructional methods and procedures appropriate for the situation when learning or teaching new things.

Speaking -- Talking to others to convey information effectively.

Judgment and Decision Making -- Considering the relative costs and benefits of potential actions to choose the most appropriate one.

Operations Analysis -- Analyzing needs and product requirements to create a design.

Monitoring -- Monitoring/Assessing performance of yourself, other individuals, or organizations to make improvements or take corrective action.

Writing -- Communicating effectively in writing as appropriate for the needs of the audience.

Equipment Maintenance -- Performing routine maintenance on equipment and determining when and what kind of maintenance is needed.

Operation and Control -- Controlling operations of equipment or systems.

Mathematics -- Using mathematics to solve problems.

Negotiation -- Bringing others together and trying to reconcile differences.

Persuasion -- Persuading others to change their minds or behavior.

Abilities

Near Vision -- The ability to see details at close range (within a few feet of the observer).

Problem Sensitivity -- The ability to tell when something is wrong or is likely to go wrong. It does not involve solving the problem, only recognizing there is a problem.

Oral Comprehension -- The ability to listen to and understand information and ideas presented through spoken words and sentences.

Inductive Reasoning -- The ability to combine pieces of information to form general rules or conclusions (includes finding a relationship among seemingly unrelated events).

Information Ordering -- The ability to arrange things or actions in a certain order or pattern according to a specific rule or set of rules (e.g., patterns of numbers, letters, words, pictures, mathematical operations).

Written Comprehension -- The ability to read and understand information and ideas presented in writing.

Oral Expression -- The ability to communicate information and ideas in speaking so others will understand.

Deductive Reasoning -- The ability to apply general rules to specific problems to produce answers that make sense.

Finger Dexterity -- The ability to make precisely coordinated movements of the fingers of one or both hands to grasp, manipulate, or assemble very small objects.

Flexibility of Closure -- The ability to identify or detect a known pattern (a figure, object, word, or sound) that is hidden in other distracting material.

Selective Attention -- The ability to concentrate on a task over a period of time without being distracted.

Originality -- The ability to come up with unusual or clever ideas about a given topic or situation, or to develop creative ways to solve a problem.

Visualization -- The ability to imagine how something will look after it is moved around or when its parts are moved or rearranged.

Written Expression -- The ability to communicate information and ideas in writing so others will understand.

Fluency of Ideas -- The ability to come up with a number of ideas about a topic (the number of ideas is important, not their quality, correctness, or creativity).

Category Flexibility -- The ability to generate or use different sets of rules for combining or grouping things in different ways.

Memorization -- The ability to remember information such as words, numbers, pictures, and procedures.

Speech Clarity -- The ability to speak clearly so others can understand you.

Speech Recognition -- The ability to identify and understand the speech of another person.

Perceptual Speed -- The ability to quickly and accurately compare similarities and differences among sets of letters, numbers, objects, pictures, or patterns. The things to be compared may be presented at the same time or one after the other. This ability also includes comparing a presented object with a remembered object.

Visual Color Discrimination -- The ability to match or detect differences between colors, including shades of color and brightness.

Time Sharing -- The ability to shift back and forth between two or more activities or sources of information (such as speech, sounds, touch, or other sources).

Arm-Hand Steadiness -- The ability to keep your hand and arm steady while moving your arm or while holding your arm and hand in one position.

Knowledge / Experience

Computers and Electronics -- Knowledge of circuit boards, processors, chips, electronic equipment, and computer hardware and software, including applications and programming.

Customer and Personal Service -- Knowledge of principles and processes for providing customer and personal services. This includes customer needs assessment, meeting quality standards for services, and evaluation of customer satisfaction.

Telecommunications -- Knowledge of transmission, broadcasting, switching, control, and operation of telecommunications systems.

English Language -- Knowledge of the structure and content of the English language including the meaning and spelling of words, rules of composition, and grammar.

Education and Training -- Knowledge of principles and methods for curriculum and training design, teaching and instruction for individuals and groups, and the measurement of training effects.

Engineering and Technology -- Knowledge of the practical application of engineering science and technology. This includes applying principles, techniques, procedures, and equipment to the design and production of various goods and services.

Administration and Management -- Knowledge of business and management principles involved in strategic planning, resource allocation, human resources modeling, leadership technique, production methods, and coordination of people and resources.

Mathematics -- Knowledge of arithmetic, algebra, geometry, calculus, statistics, and their applications.

Basics of Network

A network is any collection of independent computers that communicate with one another over a shared network medium. A computer network is a collection of two or more connected computers. When these computers are joined in a network, people can share files and peripherals such as modems, printers, tape backup drives, or CD-ROM drives. When networks at multiple locations are connected using services available from phone companies, people can send e-mail, share links to the global Internet, or conduct video conferences in real time with other remote users. When a network becomes open sourced it can be managed properly with online collaboration software. As companies rely on applications like electronic mail and database management for core business operations, computer networking becomes increasingly more important. Every network includes: At least two computers Server or Client workstation. Networking Interface Card's (NIC) A connection medium, usually a wire or cable, although wireless communication between networked computers and peripherals is also possible. Network Operating system software, such as Microsoft Windows NT or 2000, Novell NetWare, Unix and Linux. Types of Networks: LANs (Local Area Networks) A network is any collection of independent computers that communicate with one another over a shared network medium. LANs are networks usually confined to a geographic area, such as a single building or a college campus. LANs can be small, linking as few as three computers, but often link hundreds of computers used by thousands of people. The development of standard networking protocols and media has resulted in worldwide proliferation of LANs throughout business and educational organizations. WANs (Wide Area Networks) Wide area networking combines multiple LANs that are geographically separate. This is accomplished by connecting the different LANs using services such as dedicated leased phone lines, dial-up phone lines (both synchronous and asynchronous), satellite links, and data packet carrier services. Wide area networking can be as simple as a modem and remote access server for employees to dial into, or it can be as complex as hundreds of branch offices globally linked using special routing protocols and filters to minimize the expense of sending data sent over vast distances. Internet The Internet is a system of linked networks that are worldwide in scope and facilitate data communication services such as remote login, file transfer, electronic mail, the World Wide Web and newsgroups. With the meteoric rise in demand for connectivity, the Internet has become a communications highway for millions of users. The Internet was initially restricted to military and academic institutions, but now it is a full-fledged conduit for any and all forms of information and commerce. Internet websites now provide personal, educational, political and economic resources to every corner of the planet. Intranet With the advancements made in browser-based software for the Internet, many private organizations are implementing intranets. An intranet is a private network utilizing Internet-type tools, but available only within that organization. For large organizations, an intranet provides an easy access mode to corporate information for employees. MANs (Metropolitan area Networks) The refers to a network of computers with in a City. VPN (Virtual Private Network) VPN uses a technique known as tunneling to transfer data securely on the Internet to a remote access server on your workplace network. Using a VPN helps you save money by using the public Internet instead of making long–distance phone calls to connect securely with your private network. There are two ways to create a VPN connection, by dialing an Internet service provider (ISP), or connecting directly to Internet. Categories of Network: Network can be divided in to two main categories: Peer-to-peer. Server – based. In peer-to-peer networking there are no dedicated servers or hierarchy among the computers. All of the computers are equal and therefore known as peers. Normally each computer serves as Client/Server and there is no one assigned to be an administrator responsible for the entire network. Peer-to-peer networks are good choices for needs of small organizations where the users are allocated in the same general area, security is not an issue and the organization and the network will have limited growth within the foreseeable future. The term Client/server refers to the concept of sharing the work involved in processing data between the client computer and the most powerful server computer. The client/server network is the most efficient way to provide: Databases and management of applications such as Spreadsheets, Accounting, Communications and Document management. Network management. Centralized file storage. The client/server model is basically an implementation of distributed or cooperative processing. At the heart of the model is the concept of splitting application functions between a client and a server processor. The division of labor between the different processors enables the application designer to place an application function on the processor that is most appropriate for that function. This lets the software designer optimize the use of processors--providing the greatest possible return on investment for the hardware. Client/server application design also lets the application provider mask the actual location of application function. The user often does not know where a specific operation is executing. The entire function may execute in either the PC or server, or the function may be split between them. This masking of application function locations enables system implementers to upgrade portions of a system over time with a minimum disruption of application operations, while protecting the investment in existing hardware and software. The OSI Model: Open System Interconnection (OSI) reference model has become an International standard and serves as a guide for networking. This model is the best known and most widely used guide to describe networking environments. Vendors design network products based on the specifications of the OSI model. It provides a description of how network hardware and software work together in a layered fashion to make communications possible. It also helps with trouble shooting by providing a frame of reference that describes how components are supposed to function. There are seven to get familiar with and these are the physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and the application layer. Physical Layer, is just that the physical parts of the network such as wires, cables, and there media along with the length. Also this layer takes note of the electrical signals that transmit data throughout system. Data Link Layer, this layer is where we actually assign meaning to the electrical signals in the network. The layer also determines the size and format of data sent to printers, and other devices. Also I don't want to forget that these are also called nodes in the network. Another thing to consider in this layer is will also allow and define the error detection and correction schemes that insure data was sent and received. Network Layer, this layer provides the definition for the connection of two dissimilar networks. Transport Layer, this layer allows data to be broken into smaller packages for data to be distributed and addressed to other nodes (workstations). Session Layer, this layer helps out with the task to carry information from one node (workstation) to another node (workstation). A session has to be made before we can transport information to another computer. Presentation Layer, this layer is responsible to code and decode data sent to the node. Application Layer, this layer allows you to use an application that will communicate with say the operation system of a server. A good example would be using your web browser to interact with the operating system on a server such as Windows NT, which in turn gets the data you requested. Network Architectures: Ethernet Ethernet is the most popular physical layer LAN technology in use today. Other LAN types include Token Ring, Fast Ethernet, Fiber Distributed Data Interface (FDDI), Asynchronous Transfer Mode (ATM) and LocalTalk. Ethernet is popular because it strikes a good balance between speed, cost and ease of installation. These benefits, combined with wide acceptance in the computer marketplace and the ability to support virtually all popular network protocols, make Ethernet an ideal networking technology for most computer users today. The Institute for Electrical and Electronic Engineers (IEEE) defines the Ethernet standard as IEEE Standard 802.3. This standard defines rules for configuring an Ethernet network as well as specifying how elements in an Ethernet network interact with one another. By adhering to the IEEE standard, network equipment and network protocols can communicate efficiently. Fast Ethernet For Ethernet networks that need higher transmission speeds, the Fast Ethernet standard (IEEE 802.3u) has been established. This standard raises the Ethernet speed limit from 10 Megabits per second (Mbps) to 100 Mbps with only minimal changes to the existing cable structure. There are three types of Fast Ethernet: 100BASE-TX for use with level 5 UTP cable, 100BASE-FX for use with fiber-optic cable, and 100BASE-T4 which utilizes an extra two wires for use with level 3 UTP cable. The 100BASE-TX standard has become the most popular due to its close compatibility with the 10BASE-T Ethernet standard. For the network manager, the incorporation of Fast Ethernet into an existing configuration presents a host of decisions. Managers must determine the number of users in each site on the network that need the higher throughput, decide which segments of the backbone need to be reconfigured specifically for 100BASE-T and then choose the necessary hardware to connect the 100BASE-T segments with existing 10BASE-T segments. Gigabit Ethernet is a future technology that promises a migration path beyond Fast Ethernet so the next generation of networks will support even higher data transfer speeds. Token Ring Token Ring is another form of network configuration which differs from Ethernet in that all messages are transferred in a unidirectional manner along the ring at all times. Data is transmitted in tokens, which are passed along the ring and viewed by each device. When a device sees a message addressed to it, that device copies the message and then marks that message as being read. As the message makes its way along the ring, it eventually gets back to the sender who now notes that the message was received by the intended device. The sender can then remove the message and free that token for use by others. Various PC vendors have been proponents of Token Ring networks at different times and thus these types of networks have been implemented in many organizations. FDDI FDDI (Fiber-Distributed Data Interface) is a standard for data transmission on fiber optic lines in a local area network that can extend in range up to 200 km (124 miles). The FDDI protocol is based on the token ring protocol. In addition to being large geographically, an FDDI local area network can support thousands of users. Protocols: Network protocols are standards that allow computers to communicate. A protocol defines how computers identify one another on a network, the form that the data should take in transit, and how this information is processed once it reaches its final destination. Protocols also define procedures for handling lost or damaged transmissions or "packets." TCP/IP (for UNIX, Windows NT, Windows 95 and other platforms), IPX (for Novell NetWare), DECnet (for networking Digital Equipment Corp. computers), AppleTalk (for Macintosh computers), and NetBIOS/NetBEUI (for LAN Manager and Windows NT networks) are the main types of network protocols in use today. Although each network protocol is different, they all share the same physical cabling. This common method of accessing the physical network allows multiple protocols to peacefully coexist over the network media, and allows the builder of a network to use common hardware for a variety of protocols. This concept is known as "protocol independence," Some Important Protocols and their job: Protocol Acronym Its Job Point-To-Point TCP/IP The backbone protocol of the internet. Popular also for intranets using the internet Transmission Control Protocol/internet Protocol TCP/IP The backbone protocol of the internet. Popular also for intranets using the internet Internetwork Package Exchange/Sequenced Packet Exchange IPX/SPX This is a standard protocol for Novell Network Operating System NetBIOS Extended User Interface NetBEUI This is a Microsoft protocol that doesn't support routing to other networks File Transfer Protocol FTP Used to send and receive files from a remote host Hyper Text Transfer Protocol HTTP Used for the web to send documents that are encoded in HTML. Network File Services NFS Allows network nodes or workstations to access files and drives as if they were their own. Simple Mail Transfer Protocol SMTP Used to send Email over a network Telnet Used to connect to a host and emulate a terminal that the remote server can recognize Introduction to TCP/IP Networks: TCP/IP-based networks play an increasingly important role in computer networks. Perhaps one reason for their appeal is that they are based on an open specification that is not controlled by any vendor. What Is TCP/IP? TCP stands for Transmission Control Protocol and IP stands for Internet Protocol. The term TCP/IP is not limited just to these two protocols, however. Frequently, the term TCP/IP is used to refer to a group of protocols related to the TCP and IP protocols such as the User Datagram Protocol (UDP), File Transfer Protocol (FTP), Terminal Emulation Protocol (TELNET), and so on. The Origins of TCP/IP In the late 1960s, DARPA (the Defense Advanced Research Project Agency), in the United States, noticed that there was a rapid proliferation of computers in military communications. Computers, because they can be easily programmed, provide flexibility in achieving network functions that is not available with other types of communications equipment. The computers then used in military communications were manufactured by different vendors and were designed to interoperate with computers from that vendor only. Vendors used proprietary protocols in their communications equipment. The military had a multi vendor network but no common protocol to support the heterogeneous equipment from different vendors Net work Cables and Stuff: In the network you will commonly find three types of cables used these are the, coaxial cable, fiber optic and twisted pair. Thick Coaxial Cable This type cable is usually yellow in color and used in what is called thicknets, and has two conductors. This coax can be used in 500-meter lengths. The cable itself is made up of a solid center wire with a braided metal shield and plastic sheathing protecting the rest of the wire. Thin Coaxial Cable As with the thick coaxial cable is used in thicknets the thin version is used in thinnets. This type cable is also used called or referred to as RG-58. The cable is really just a cheaper version of the thick cable. Fiber Optic Cable As we all know fiber optics are pretty darn cool and not cheap. This cable is smaller and can carry a vast amount of information fast and over long distances. Twisted Pair Cables These come in two flavors of unshielded and shielded. Shielded Twisted Pair (STP) Is more common in high-speed networks. The biggest difference you will see in the UTP and STP is that the STP use's metallic shield wrapping to protect the wire from interference. -Something else to note about these cables is that they are defined in numbers also. The bigger the number the better the protection from interference. Most networks should go with no less than a CAT 3 and CAT 5 is most recommended. -Now you know about cables we need to know about connectors. This is pretty important and you will most likely need the RJ-45 connector. This is the cousin of the phone jack connector and looks real similar with the exception that the RJ-45 is bigger. Most commonly your connector are in two flavors and this is BNC (Bayonet Naur Connector) used in thicknets and the RJ-45 used in smaller networks using UTP/STP. Unshielded Twisted Pair (UTP) This is the most popular form of cables in the network and the cheapest form that you can go with. The UTP has four pairs of wires and all inside plastic sheathing. The biggest reason that we call it Twisted Pair is to protect the wires from interference from themselves. Each wire is only protected with a thin plastic sheath. Ethernet Cabling Now to familiarize you with more on the Ethernet and it's cabling we need to look at the 10's. 10Base2, is considered the thin Ethernet, thinnet, and thinwire which uses light coaxial cable to create a 10 Mbps network. The cable segments in this network can't be over 185 meters in length. These cables connect with the BNC connector. Also as a note these unused connection must have a terminator, which will be a 50-ohm terminator. 10Base5, this is considered a thicknet and is used with coaxial cable arrangement such as the BNC connector. The good side to the coaxial cable is the high-speed transfer and cable segments can be up to 500 meters between nodes/workstations. You will typically see the same speed as the 10Base2 but larger cable lengths for more versatility. 10BaseT, the “T” stands for twisted as in UTP (Unshielded Twisted Pair) and uses this for 10Mbps of transfer. The down side to this is you can only have cable lengths of 100 meters between nodes/workstations. The good side to this network is they are easy to set up and cheap! This is why they are so common an ideal for small offices or homes. 100BaseT, is considered Fast Ethernet uses STP (Shielded Twisted Pair) reaching data transfer of 100Mbps. This system is a little more expensive but still remains popular as the 10BaseT and cheaper than most other type networks. This on of course would be the cheap fast version. 10BaseF, this little guy has the advantage of fiber optics and the F stands for just that. This arrangement is a little more complicated and uses special connectors and NIC's along with hubs to create its network. Pretty darn neat and not to cheap on the wallet. An important part of designing and installing an Ethernet is selecting the appropriate Ethernet medium. There are four major types of media in use today: Thickwire for 10BASE5 networks, thin coax for 10BASE2 networks, unshielded twisted pair (UTP) for 10BASE-T networks and fiber optic for 10BASE-FL or Fiber-Optic Inter-Repeater Link (FOIRL) networks. This wide variety of media reflects the evolution of Ethernet and also points to the technology's flexibility. Thickwire was one of the first cabling systems used in Ethernet but was expensive and difficult to use. This evolved to thin coax, which is easier to work with and less expensive. Network Topologies: What is a Network topology? A network topology is the geometric arrangement of nodes and cable links in a LAN, There are three topology's to think about when you get into networks. These are the star, rind, and the bus. Star, in a star topology each node has a dedicated set of wires connecting it to a central network hub. Since all traffic passes through the hub, the hub becomes a central point for isolating network problems and gathering network statistics. Ring, a ring topology features a logically closed loop. Data packets travel in a single direction around the ring from one network device to the next. Each network device acts as a repeater, meaning it regenerates the signal Bus, the bus topology, each node (computer, server, peripheral etc.) attaches directly to a common cable. This topology most often serves as the backbone for a network. In some instances, such as in classrooms or labs, a bus will connect small workgroups Collisions: Ethernet is a shared media, so there are rules for sending packets of data to avoid conflicts and protect data integrity. Nodes determine when the network is available for sending packets. It is possible that two nodes at different locations attempt to send data at the same time. When both PCs are transferring a packet to the network at the same time, a collision will result. Minimizing collisions is a crucial element in the design and operation of networks. Increased collisions are often the result of too many users on the network, which results in a lot of contention for network bandwidth. This can slow the performance of the network from the user's point of view. Segmenting the network, where a network is divided into different pieces joined together logically with a bridge or switch, is one way of reducing an overcrowded network. Ethernet Products: The standards and technology that have just been discussed help define the specific products that network managers use to build Ethernet networks. The following text discusses the key products needed to build an Ethernet LAN. Transceivers Transceivers are used to connect nodes to the various Ethernet media. Most computers and network interface cards contain a built-in 10BASE-T or 10BASE2 transceiver, allowing them to be connected directly to Ethernet without requiring an external transceiver. Many Ethernet devices provide an AUI connector to allow the user to connect to any media type via an external transceiver. The AUI connector consists of a 15-pin D-shell type connector, female on the computer side, male on the transceiver side. Thickwire (10BASE5) cables also use transceivers to allow connections. For Fast Ethernet networks, a new interface called the MII (Media Independent Interface) was developed to offer a flexible way to support 100 Mbps connections. The MII is a popular way to connect 100BASE-FX links to copper-based Fast Ethernet devices. Network Interface Cards: Network interface cards, commonly referred to as NICs, and are used to connect a PC to a network. The NIC provides a physical connection between the networking cable and the computer's internal bus. Different computers have different bus architectures; PCI bus master slots are most commonly found on 486/Pentium PCs and ISA expansion slots are commonly found on 386 and older PCs. NICs come in three basic varieties: 8-bit, 16-bit, and 32-bit. The larger the number of bits that can be transferred to the NIC, the faster the NIC can transfer data to the network cable. Many NIC adapters comply with Plug-n-Play specifications. On these systems, NICs are automatically configured without user intervention, while on non-Plug-n-Play systems, configuration is done manually through a setup program and/or DIP switches. Cards are available to support almost all networking standards, including the latest Fast Ethernet environment. Fast Ethernet NICs are often 10/100 capable, and will automatically set to the appropriate speed. Full duplex networking is another option, where a dedicated connection to a switch allows a NIC to operate at twice the speed. Hubs/Repeaters: Hubs/repeaters are used to connect together two or more Ethernet segments of any media type. In larger designs, signal quality begins to deteriorate as segments exceed their maximum length. Hubs provide the signal amplification required to allow a segment to be extended a greater distance. A hub takes any incoming signal and repeats it out all ports. Ethernet hubs are necessary in star topologies such as 10BASE-T. A multi-port twisted pair hub allows several point-to-point segments to be joined into one network. One end of the point-to-point link is attached to the hub and the other is attached to the computer. If the hub is attached to a backbone, then all computers at the end of the twisted pair segments can communicate with all the hosts on the backbone. The number and type of hubs in any one-collision domain is limited by the Ethernet rules. These repeater rules are discussed in more detail later. Network Type Max Nodes Per Segment Max Distance Per Segment 10BASE-T 10BASE2 10BASE5 10BASE-FL 2 30 100 2 100m 185m 500m 2000m Adding Speed: While repeaters allow LANs to extend beyond normal distance limitations, they still limit the number of nodes that can be supported. Bridges and switches, however, allow LANs to grow significantly larger by virtue of their ability to support full Ethernet segments on each port. Additionally, bridges and switches selectively filter network traffic to only those packets needed on each segment - this significantly increases throughput on each segment and on the overall network. By providing better performance and more flexibility for network topologies, bridges and switches will continue to gain popularity among network managers. Bridges: The function of a bridge is to connect separate networks together. Bridges connect different networks types (such as Ethernet and Fast Ethernet) or networks of the same type. Bridges map the Ethernet addresses of the nodes residing on each network segment and allow only necessary traffic to pass through the bridge. When a packet is received by the bridge, the bridge determines the destination and source segments. If the segments are the same, the packet is dropped ("filtered"); if the segments are different, then the packet is "forwarded" to the correct segment. Additionally, bridges do not forward bad or misaligned packets. Bridges are also called "store-and-forward" devices because they look at the whole Ethernet packet before making filtering or forwarding decisions. Filtering packets, and regenerating forwarded packets enable bridging technology to split a network into separate collision domains. This allows for greater distances and more repeaters to be used in the total network design. Ethernet Switches: Ethernet switches are an expansion of the concept in Ethernet bridging. LAN switches can link four, six, ten or more networks together, and have two basic architectures: cut-through and store-and-forward. In the past, cut-through switches were faster because they examined the packet destination address only before forwarding it on to its destination segment. A store-and-forward switch, on the other hand, accepts and analyzes the entire packet before forwarding it to its destination. It takes more time to examine the entire packet, but it allows the switch to catch certain packet errors and keep them from propagating through the network. Both cut-through and store-and-forward switches separate a network into collision domains, allowing network design rules to be extended. Each of the segments attached to an Ethernet switch has a full 10 Mbps of bandwidth shared by fewer users, which results in better performance (as opposed to hubs that only allow bandwidth sharing from a single Ethernet). Newer switches today offer high-speed links, FDDI, Fast Ethernet or ATM. These are used to link switches together or give added bandwidth to high-traffic servers. A network composed of a number of switches linked together via uplinks is termed a "collapsed backbone" network. Routers: Routers filter out network traffic by specific protocol rather than by packet address. Routers also divide networks logically instead of physically. An IP router can divide a network into various subnets so that only traffic destined for particular IP addresses can pass between segments. Network speed often decreases due to this type of intelligent forwarding. Such filtering takes more time than that exercised in a switch or bridge, which only looks at the Ethernet address. However, in more complex networks, overall efficiency is improved by using routers. What is a network firewall? A firewall is a system or group of systems that enforces an access control policy between two networks. The actual means by which this is accomplished varies widely, but in principle, the firewall can be thought of as a pair of mechanisms: one which exists to block traffic, and the other which exists to permit traffic. Some firewalls place a greater emphasis on blocking traffic, while others emphasize permitting traffic. Probably the most important thing to recognize about a firewall is that it implements an access control policy. If you don't have a good idea of what kind of access you want to allow or to deny, a firewall really won't help you. It's also important to recognize that the firewall's configuration, because it is a mechanism for enforcing policy, imposes its policy on everything behind it. Administrators for firewalls managing the connectivity for a large number of hosts therefore have a heavy responsibility. Network Design Criteria: Ethernets and Fast Ethernets have design rules that must be followed in order to function correctly. Maximum number of nodes, number of repeaters and maximum segment distances are defined by the electrical and mechanical design properties of each type of Ethernet and Fast Ethernet media. A network using repeaters, for instance, functions with the timing constraints of Ethernet. Although electrical signals on the Ethernet media travel near the speed of light, it still takes a finite time for the signal to travel from one end of a large Ethernet to another. The Ethernet standard assumes it will take roughly 50 microseconds for a signal to reach its destination. Ethernet is subject to the "5-4-3" rule of repeater placement: the network can only have five segments connected; it can only use four repeaters; and of the five segments, only three can have users attached to them; the other two must be inter-repeater links. If the design of the network violates these repeater and placement rules, then timing guidelines will not be met and the sending station will resend that packet. This can lead to lost packets and excessive resent packets, which can slow network performance and create trouble for applications. Fast Ethernet has modified repeater rules, since the minimum packet size takes less time to transmit than regular Ethernet. The length of the network links allows for a fewer number of repeaters. In Fast Ethernet networks, there are two classes of repeaters. Class I repeaters have a latency of 0.7 microseconds or less and are limited to one repeater per network. Class II repeaters have a latency of 0.46 microseconds or less and are limited to two repeaters per network. The following are the distance (diameter) characteristics for these types of Fast Ethernet repeater combinations: Fast Ethernet Copper Fiber No Repeaters One Class I Repeater One Class II Repeater Two Class II Repeaters 100m 200m 200m 205m 412m* 272m 272m 228m * Full Duplex Mode 2 km When conditions require greater distances or an increase in the number of nodes/repeaters, then a bridge, router or switch can be used to connect multiple networks together. These devices join two or more separate networks, allowing network design criteria to be restored. Switches allow network designers to build large networks that function well. The reduction in costs of bridges and switches reduces the impact of repeater rules on network design. Each network connected via one of these devices is referred to as a separate collision domain in the overall network. Types of Servers: Device Servers A device server is defined as a specialized, network-based hardware device designed to perform a single or specialized set of server functions. It is characterized by a minimal operating architecture that requires no per seat network operating system license, and client access that is independent of any operating system or proprietary protocol. In addition the device server is a "closed box," delivering extreme ease of installation, minimal maintenance, and can be managed by the client remotely via a Web browser. Print servers, terminal servers, remote access servers and network time servers are examples of device servers which are specialized for particular functions. Each of these types of servers has unique configuration attributes in hardware or software that help them to perform best in their particular arena. Print Servers Print servers allow printers to be shared by other users on the network. Supporting either parallel and/or serial interfaces, a print server accepts print jobs from any person on the network using supported protocols and manages those jobs on each appropriate printer. Print servers generally do not contain a large amount of memory; printers simply store information in a queue. When the desired printer becomes available, they allow the host to transmit the data to the appropriate printer port on the server. The print server can then simply queue and print each job in the order in which print requests are received, regardless of protocol used or the size of the job. Multiport Device Servers Devices that are attached to a network through a multiport device server can be shared between terminals and hosts at both the local site and throughout the network. A single terminal may be connected to several hosts at the same time (in multiple concurrent sessions), and can switch between them. Multiport device servers are also used to network devices that have only serial outputs. A connection between serial ports on different servers is opened, allowing data to move between the two devices. Given its natural translation ability, a multi-protocol multiport device server can perform conversions between the protocols it knows, like LAT and TCP/IP. While server bandwidth is not adequate for large file transfers, it can easily handle host-to-host inquiry/response applications, electronic mailbox checking, etc. And it is far more economical than the alternatives of acquiring expensive host software and special-purpose converters. Multiport device and print servers give their users greater flexibility in configuring and managing their networks. Whether it is moving printers and other peripherals from one network to another, expanding the dimensions of interoperability or preparing for growth, multiport device servers can fulfill your needs, all without major rewiring. Access Servers While Ethernet is limited to a geographic area, remote users such as traveling sales people need access to network-based resources. Remote LAN access, or remote access, is a popular way to provide this connectivity. Access servers use telephone services to link a user or office with an office network. Dial-up remote access solutions such as ISDN or asynchronous dial introduce more flexibility. Dial-up remote access offers both the remote office and the remote user the economy and flexibility of "pay as you go" telephone services. ISDN is a special telephone service that offers three channels, two 64 Kbps "B" channels for user data and a "D" channel for setting up the connection. With ISDN, the B channels can be combined for double bandwidth or separated for different applications or users. With asynchronous remote access, regular telephone lines are combined with modems and remote access servers to allow users and networks to dial anywhere in the world and have data access. Remote access servers provide connection points for both dial-in and dial-out applications on the network to which they are attached. These hybrid devices route and filter protocols and offer other services such as modem pooling and terminal/printer services. For the remote PC user, one can connect from any available telephone jack (RJ45), including those in a hotel rooms or on most airplanes. Network Time Servers A network time server is a server specialized in the handling of timing information from sources such as satellites or radio broadcasts and is capable of providing this timing data to its attached network. Specialized protocols such as NTP or udp/time allow a time server to communicate to other network nodes ensuring that activities that must be coordinated according to their time of execution are synchronized correctly. GPS satellites are one source of information that can allow global installations to achieve constant timing. IP Addressing: An IP (Internet Protocol) address is a unique identifier for a node or host connection on an IP network. An IP address is a 32 bit binary number usually represented as 4 decimal values, each representing 8 bits, in the range 0 to 255 (known as octets) separated by decimal points. This is known as "dotted decimal" notation. Example: 140.179.220.200 It is sometimes useful to view the values in their binary form. 140 .179 .220 .200 10001100.10110011.11011100.11001000 Every IP address consists of two parts, one identifying the network and one identifying the node. The Class of the address and the subnet mask determine which part belongs to the network address and which part belongs to the node address. Address Classes: There are 5 different address classes. You can determine which class any IP address is in by examining the first 4 bits of the IP address. Class A addresses begin with 0xxx, or 1 to 126 decimal. Class B addresses begin with 10xx, or 128 to 191 decimal. Class C addresses begin with 110x, or 192 to 223 decimal. Class D addresses begin with 1110, or 224 to 239 decimal. Class E addresses begin with 1111, or 240 to 254 decimal. Addresses beginning with 01111111, or 127 decimal, are reserved for loopback and for internal testing on a local machine. [You can test this: you should always be able to ping 127.0.0.1, which points to yourself] Class D addresses are reserved for multicasting. Class E addresses are reserved for future use. They should not be used for host addresses. Now we can see how the Class determines, by default, which part of the IP address belongs to the network (N) and which part belongs to the node (n). Class A -- NNNNNNNN.nnnnnnnn.nnnnnnn.nnnnnnn Class B -- NNNNNNNN.NNNNNNNN.nnnnnnnn.nnnnnnnn Class C -- NNNNNNNN.NNNNNNNN.NNNNNNNN.nnnnnnnn In the example, 140.179.220.200 is a Class B address so by default the Network part of the address (also known as the Network Address) is defined by the first two octets (140.179.x.x) and the node part is defined by the last 2 octets (x.x.220.200). In order to specify the network address for a given IP address, the node section is set to all "0"s. In our example, 140.179.0.0 specifies the network address for 140.179.220.200. When the node section is set to all "1"s, it specifies a broadcast that is sent to all hosts on the network. 140.179.255.255 specifies the example broadcast address. Note that this is true regardless of the length of the node section. Private Subnets: There are three IP network addresses reserved for private networks. The addresses are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. They can be used by anyone setting up internal IP networks, such as a lab or home LAN behind a NAT or proxy server or a router. It is always safe to use these because routers on the Internet will never forward packets coming from these addresses Subnetting an IP Network can be done for a variety of reasons, including organization, use of different physical media (such as Ethernet, FDDI, WAN, etc.), preservation of address space, and security. The most common reason is to control network traffic. In an Ethernet network, all nodes on a segment see all the packets transmitted by all the other nodes on that segment. Performance can be adversely affected under heavy traffic loads, due to collisions and the resulting retransmissions. A router is used to connect IP networks to minimize the amount of traffic each segment must receive. Subnet Masking Applying a subnet mask to an IP address allows you to identify the network and node parts of the address. The network bits are represented by the 1s in the mask, and the node bits are represented by the 0s. Performing a bitwise logical AND operation between the IP address and the subnet mask results in the Network Address or Number. For example, using our test IP address and the default Class B subnet mask, we get: 10001100.10110011.11110000.11001000 140.179.240.200 Class B IP Address 11111111.11111111.00000000.00000000 255.255.000.000 Default Class B Subnet Mask 10001100.10110011.00000000.00000000 140.179.000.000 Network Address Default subnet masks: Class A - 255.0.0.0 - 11111111.00000000.00000000.00000000 Class B - 255.255.0.0 - 11111111.11111111.00000000.00000000 Class C - 255.255.255.0 - 11111111.11111111.11111111.00000000 CIDR -- Classless InterDomain Routing. CIDR was invented several years ago to keep the internet from running out of IP addresses. The "classful" system of allocating IP addresses can be very wasteful; anyone who could reasonably show a need for more that 254 host addresses was given a Class B address block of 65533 host addresses. Even more wasteful were companies and organizations that were allocated Class A address blocks, which contain over 16 Million host addresses! Only a tiny percentage of the allocated Class A and Class B address space has ever been actually assigned to a host computer on the Internet. People realized that addresses could be conserved if the class system was eliminated. By accurately allocating only the amount of address space that was actually needed, the address space crisis could be avoided for many years. This was first proposed in 1992 as a scheme called Supernetting. The use of a CIDR notated address is the same as for a Classful address. Classful addresses can easily be written in CIDR notation (Class A = /8, Class B = /16, and Class C = /24) It is currently almost impossible for an individual or company to be allocated their own IP address blocks. You will simply be told to get them from your ISP. The reason for this is the ever-growing size of the internet routing table. Just 5 years ago, there were less than 5000 network routes in the entire Internet. Today, there are over 90,000. Using CIDR, the biggest ISPs are allocated large chunks of address space (usually with a subnet mask of /19 or even smaller); the ISP's customers (often other, smaller ISPs) are then allocated networks from the big ISP's pool. That way, all the big ISP's customers (and their customers, and so on) are accessible via 1 network route on the Internet. It is expected that CIDR will keep the Internet happily in IP addresses for the next few years at least. After that, IPv6, with 128 bit addresses, will be needed. Under IPv6, even sloppy address allocation would comfortably allow a billion unique IP addresses for every person on earth Examining your network with commands: Ping PING is used to check for a response from another computer on the network. It can tell you a great deal of information about the status of the network and the computers you are communicating with. Ping returns different responses depending on the computer in question. The responses are similar depending on the options used. Ping uses IP to request a response from the host. It does not use TCP .It takes its name from a submarine sonar search - you send a short sound burst and listen for an echo - a ping - coming back. In an IP network, `ping' sends a short data burst - a single packet - and listens for a single packet in reply. Since this tests the most basic function of an IP network (delivery of single packet), it's easy to see how you can learn a lot from some `pings'. To stop ping, type control-c. This terminates the program and prints out a nice summary of the number of packets transmitted, the number received, and the percentage of packets lost, plus the minimum, average, and maximum round-trip times of the packets. Sample ping session PING localhost (127.0.0.1): 56 data bytes 64 bytes from 127.0.0.1: icmp_seq=0 ttl=255 time=2 ms 64 bytes from 127.0.0.1: icmp_seq=1 ttl=255 time=2 ms 64 bytes from 127.0.0.1: icmp_seq=2 ttl=255 time=2 ms 64 bytes from 127.0.0.1: icmp_seq=3 ttl=255 time=2 ms 64 bytes from 127.0.0.1: icmp_seq=4 ttl=255 time=2 ms 64 bytes from 127.0.0.1: icmp_seq=5 ttl=255 time=2 ms 64 bytes from 127.0.0.1: icmp_seq=6 ttl=255 time=2 ms 64 bytes from 127.0.0.1: icmp_seq=7 ttl=255 time=2 ms 64 bytes from 127.0.0.1: icmp_seq=8 ttl=255 time=2 ms 64 bytes from 127.0.0.1: icmp_seq=9 ttl=255 time=2 ms localhost ping statistics 10 packets transmitted, 10 packets received, 0% packet loss round-trip min/avg/max = 2/2/2 ms meikro$ The Time To Live (TTL) field can be interesting. The main purpose of this is so that a packet doesn't live forever on the network and will eventually die when it is deemed "lost." But for us, it provides additional information. We can use the TTL to determine approximately how many router hops the packet has gone through. In this case it's 255 minus N hops, where N is the TTL of the returning Echo Replies. If the TTL field varies in successive pings, it could indicate that the successive reply packets are going via different routes, which isn't a great thing. The time field is an indication of the round-trip time to get a packet to the remote host. The reply is measured in milliseconds. In general, it's best if round-trip times are under 200 milliseconds. The time it takes a packet to reach its destination is called latency. If you see a large variance in the round-trip times (which is called "jitter"), you are going to see poor performance talking to the host NSLOOKUP NSLOOKUP is an application that facilitates looking up hostnames on the network. It can reveal the IP address of a host or, using the IP address, return the host name. It is very important when troubleshooting problems on a network that you can verify the components of the networking process. Nslookup allows this by revealing details within the infrastructure. NETSTAT NETSTAT is used to look up the various active connections within a computer. It is helpful to understand what computers or networks you are connected to. This allows you to further investigate problems. One host may be responding well but another may be less responsive. IPconfig This is a Microsoft windows NT, 2000 command. It is very useful in determining what could be wrong with a network. This command when used with the /all switch, reveal enormous amounts of troubleshooting information within the system. Windows 2000 IP Configuration Host Name . . . . . . . . . . . . : cowder Primary DNS Suffix . . . . . . . : Node Type . . . . . . . . . . . . : Broadcast IP Routing Enabled. . . . . . . . : No WINS Proxy Enabled. . . . . . . . : No WINS Proxy Enabled. . . . . . . . : No Connection-specific DNS Suffix . : Description . . . . . . . . . . . : WAN (PPP/SLIP) Interface Physical Address. . . . . . . . . : 00-53-45-00-00-00 DHCP Enabled. . . . . . . . . . . : No IP Address. . . . . . . . . . . . : 12.90.108.123 Subnet Mask . . . . . . . . . . . : 255.255.255.255 Default Gateway . . . . . . . . . : 12.90.108.125 DNS Servers . . . . . . . . . . . : 12.102.244.2 204.127.129.2   Traceroute Traceroute on Unix and Linux (or tracert in the Microsoft world) attempts to trace the current network path to a destination. Here is an example of a traceroute run to www.berkeley.edu: