NETWORKING ESSENTIALS

Transcription

1 Models of network There are three types of network models 1. Centralized Computing 2. Work Group (peer-to-peer) 3. Domain (Client-Server) Centralized Computing: It is the oldest model of networking based on the idea of having one very large and powerful central computer, to which a number of computer terminals are directly connected. In the early days of computing, this central computer would invariably have been a mainframe computer (often called the host computer). This arrangement allowed many users to access the resources of the "host" mainframe computer simultaneously Workgroup (Peer to peer): A workgroup is a collection of computers on a local area network (LAN) that share common resources and responsibilities. You simply use the same Workgroup for all the computers and a unique name for each computer. Being a peer-to-peer (P2P) network design all computers acts as a client because there is no centralized server. The user on each computer determines which data on that computer is shared on the network. Security is also managed by the user of the devices. The Microsoft Windows family of operating systems supports assigning of computers to named workgroups. Macintosh networks offer a similar capability through the use of AppleTalk zones. The Open Source software package Samba allows UNIX and Linux systems to join existing Windows workgroups. Criteria for selecting peer to peer 1. Where 10 to 15 or fewer users will be sharing resources. 2. No server is available. 3. Nobody has the time or knowledge to act as a network administrator. 4. There is little or no concerns about security (security in data processing is the ability to protect data from unauthorized access or, theft or damage) 5. The organization and the network will experience only limited growth within the foreseeable future. Advantages of using peer to peer They are easy to configure Computers communicate easily. They don t require additional server hardware or software Users can manage their own resources. They don t require a network administrator They reduce total cost of network setup. Disadvantages of using peer to peer 1. They provide a limited number of connections for shared resources. 2. Computers with shared resources suffer from sluggish performance. 3. They don t allow for central management 4. Users are responsible for managing resources. These resources include data in shared directories, printers, fax cards, and so on. 5. They offer very poor security. 1

2 Domain (Client/Server Model) It is the most common type of network architecture today that provides centralized data storage, security. In client-server model one or more computers work as servers and other computers work as clients. A client is a machine, typically a personal computer (or mobile, desktop or laptop) that is equipped with network software applications. These applications are designed to request and receive data over the span of the network. The server computer controls the whole network, this enables server to keep profile of users, data, and software etc completely in tacked and organized. A server is a storehouse of files, folders, databases and even more complicated applications. A server is more powerful than a client and can support and process the requests of a large number of clients. Operating systems of servers are different from that of clients. Client Operating systems: Windows 95, 98, Me, 2000, XP, Vista, 7 Server Operating Systems: Windows NT, server2000, 2003, 2008 Disadvantages Cost: - More expensive in terms of hardware and network operating system. Complexity: - Experienced system administrators are required to manage the systems. Dependence: - When server goes down, operations will cease across the network. Advantages 1. They are best suited for 10 or more users. 2. Security: - All major server based systems provides sophisticated security. 3. Administration: - Servers are centralized making them easier to manage. 4. Stability: - Server based systems are designed to support a wide range of organization sizes. Additional servers are added to increase capacity. 5. Client server networks offer centralized backup where data can be stored in one server. 6. Flexibility - New technology can be easily integrated into the system. 7. Accessibility - Server can be accessed remotely and across multiple platforms. A Windows domain is a logical group of computers running versions of the Microsoft Windows operating system that share a central directory database. This central database known as Active Directory (starting with Windows 2000) contains the user accounts and security information for the resources in that domain. Each person who uses computers within a domain receives his or her own unique account, or user name. This account can then be assigned access to resources within the domain. In a domain, the directory resides on computers that are configured as "domain controllers." A domain controller is a server that manages all security-related aspects between user and domain interactions, centralizing security and administration. 2

3 A domain does not refer to a single location or specific type of network configuration. The computers in a domain can share physical proximity on a small LAN or they can be located in different parts of the world. As long as they can communicate, their physical position is irrelevant. Networking Standards: A network standard is in short a reference model to make sure products of different vendors can work together in a network; The International Organization for Standardization (ISO) lays out those standards. A network protocol is a set of rule, which govern communication between two or more devices or computer; or, a set of rule and regulation for the communication between devices within a network. For example in order for you to be able to internet you need to have the 'tcp/ip'-protocol enabled. In short, a network standard helps vendors to create products that can all work together; a network protocol allows different network devices to communicate with each other. There are a lot of different network standards that the majority of computers use. There are standards for both physical hardware and for signaling. For example, IEEE g is a wireless networking standard. It includes specifications for the type of radio that is used, how strong the signal can be amplified, a standard set of encryption schemes, etc. Another standard is Ethernet, also known as IEEE This is a standard for hardwired networks. When people talk about Cat 5 cable, this is usually what they mean. It defines what types of wiring can be used, transmission power requirements, connector styles, etc. There are also protocols. TCP/IP is basically the protocol that runs the internet and most LANs that exist today. When people talk about IP addresses, subnet masks, default gateways, etc. those usually pertain to this. Note that TCP/IP is a protocol that is used in conjunction with things like g or Ethernet. Baseband: Baseband systems use digital signaling over a single frequency. Signals flow in the form of discrete pulses of electricity or light. With baseband transmission, the entire communication channel capacity is used to transmit a single data signal. The digital signal uses the complete bandwidth of the cable, which constitutes a single channel. A cable's total bandwidth is the difference between the highest and lowest frequencies that are carried over that cable. Each device on a baseband network transmits bidirectional, and some can transmit and receive at the same time. 3

4 Bidirectional Digital Wave As the signal travels along the network cable, it gradually decreases in strength and can become distorted. If the cable length is too long, the result is a signal that is weak or distorted. The received signal may be unrecognizable or misinterpreted. As a safeguard, baseband systems sometimes use repeaters to receive an incoming signal and retransmit it at its original strength and definition to increase the practical length of a cable. It is the Digital communication technology in which the entire bandwidth of a medium such as a wire, cable, or channel, is used to transmit a single signal. Therefore, only one communication channel is available at any given time. Baseband is cheaper and simpler technology than broadband, and is employed in most types of local area networks such as Ethernet. Broad Band: Broadband systems use analog signaling and a range of frequencies. With analog transmission, the signals are continuous and no discrete. Signals flow across the physical medium in the form of electromagnetic or optical waves. With broadband transmission, signal flow is unidirectional. Unidirectional Analog Wave If sufficient total bandwidth is available, multiple analog transmission systems such as cable television and network transmissions can be supported simultaneously on the same cable. Each transmission system is allocated a part of the total bandwidth. All devices associated with a given transmission system, such as all computers using a LAN cable, must then be tuned so that they use only the frequencies that are within the allocated range. While baseband systems use repeaters, broadband systems use amplifiers to regenerate analog signals at their original strength. Because broadband transmission signal flow is unidirectional, there must be two paths for data flow in order for a signal to reach all devices. There are two common ways to do this: Mid-split broadband configuration divides the bandwidth into two channels, each using a different frequency or range of frequencies. One channel is used to transmit signals, the other to receive signals. In dual-cable broadband configuration, each device is attached to two cables. One cable is used to send and the other is used to receive. The term comes from how the high-speed systems work. Imagine your Internet connection as a highway. Your dial up connection would be a small highway with only a few lanes, so it s harder for lots of cars (data) to get through. Broadband, however, is a huge highway with lots and lots of lanes, so tons of cars (data) can go through at the same time. This makes everything go faster. Attenuation: Attenuation is a general term that refers to any reduction in the strength of a signal. Attenuation occurs with any type of signal, whether digital or analog. Sometimes called LOSS, attenuation is a natural consequence of signal transmission over long distances. The extent of attenuation is usually expressed in units called decibels (dbs). Attenuation occurs on networks for several reasons: 4

5 1. range - both wireless and wired transmissions gradually dissipate in strength over longer reaches 2. interference - on wireless networks, radio interference or physical obstructions like walls also dampen communication signals 3. wire size - on wired networks, thinner wires suffer from higher (more) attenuation than thicker wires Cross Talk: Crosstalk is a disturbance caused by the electric or magnetic fields of one telecommunication signal affecting a signal in an adjacent circuit. In a telephone circuit, crosstalk can result in your hearing part of a voice conversation from another circuit. The phenomenon that causes crosstalk is called electromagnetic interference (EMI). It can occur in microcircuits within computers and audio equipment as well as within network circuits. The term is also applied to optical signals that interfere with each other. Cables (UTP, STP, FOC& Co-axial) & connector: Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network. Unshielded Twisted Pair (UTP) Cable Shielded Twisted Pair (STP) Cable Coaxial Cable Fiber Optic Cable Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for networks 5

6 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). Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield. The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers. Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. 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. 6

7 UTP STP Media Type Max Segment Length 100m 100m Speed Cost Advantages Disadvantages Mbps Mbps Least Expensive More Expensive than UTP Easy to install;widely available and widely used Reduced crosstalk; more resistant to EMI than Thinner or UTP Susceptible to interference; can cover only a limited distance. Difficult to work with; can cover only a limited distance. Coaxial 500m(Thicknet) 185m(Thinnet) Mbps Relatively inexpensive, but more costly than UTP Less susceptible to EMI interference than other types of copper media Difficult to work with(thicknet); limited bandwidth; limited application (Thinnet); damage to cable can bring down entire network Fiber- Optic 10km, and farther (singlemode) 2km and farther (multimode) 100Mbps to 100Gbps (Singlemode) 100Mbps to 9.92Gbps (multimode) Expensive Cannot be tapped, so security is better; can be used over great distances; is not susceptible to EMI; has a higher data rate than coaxial and twisted-pair cable Difficult to terminate Networking Devices: Modem The word "modem" is a contraction of the words modulator-demodulator. A modem is typically used to send digital data over a phone line The sending modem modulates the data into a signal that is compatible with the phone line, and the receiving modem demodulates the signal back into digital data. Wireless modems convert digital data into radio signals and back. 7

8 Hub: Hub is a common connection point for devices in a network. A hub contains multiple ports Hub broadcasts the packets to all the ports including the incoming port. Repeaters: Network repeaters regenerate incoming electrical, wireless, or optical signals. With physical media like Ethernet or Wi-Fi, data transmissions can only span a limited distance before the quality of the signal degrades. Repeaters attempt to preserve signal integrity and extend the distance over which data can safely travel. Bridges Bridge is a device which connects two segments of a network. Bridges inspect incoming traffic and decide whether to forward or discard it. An Ethernet bridge, for example, inspects each incoming Ethernet frame - including the source and destination MAC addresses, and sometimes the frame size. If the destination address is not on the other side of the bridge it will not transmit the data. Packet forwarding is performed using software. Usually Bridges have 2 ports can go up to a max of 16 ports. CSU/DSU: A Channel Service Unit (CSU) is a device that connects a terminal to a digital line. A Data Service Unit (DSU) is a device that performs protective and diagnostic functions for a telecommunications line. Typically, the two devices are packaged as a single unit, CSU/DSU. You can think of a CSU/DSU as a very high-powered and expensive modem. Such a device is required for both ends of a T-1 or T-3 connection; the units at both ends must be from the same manufacturer. Network Interface Card/NIC: Short for Network Interface Card, a NIC is also commonly referred to as an Ethernet card and network adapter and is an expansion card that enables a computer to connect to a network such as a home network or the Internet using an Ethernet cable with a RJ-45 connector. Some NIC cards work with 8

9 wired connections while others are wireless. Most NICs support wired either Ethernet or Wi-Fi wireless standards. Ethernet NICs plug into the system bus of the PC and include jacks for network cables, while Wi-Fi NICs contain built-in transmitters / receivers (transceivers). Switch: A network switch is a small hardware device that joins multiple computers together within one local area network (LAN). Technically, network switches operate at layer two (Data Link Layer) of the OSI model. Network switches appear nearly identical to network hubs, but a switch generally contains more intelligence (and a slightly higher price tag) than a hub. Unlike hubs, network switches are capable of inspecting data packets as they are received, determining the source and destination device of each packet, and forwarding them appropriately. By delivering messages only to the connected device intended, a network switch conserves network bandwidth and offers generally better performance than a hub. As with hubs, Ethernet implementations of network switches are the most common. Mainstream Ethernet network switches support either 10/100 Mbps Fast Ethernet or Gigabit Ethernet (10/100/1000) standards. Different models of network switches support differing numbers of connected devices. Most consumergrade network switches provide either four or eight connections for Ethernet devices. Switches can be connected to each other, a so-called daisy chaining method to add progressively larger number of devices to a LAN. Types of Network Switches Unmanaged Network Switches Unmanaged network switches are commonly used in home networks and small businesses. It allows devices on the network to communicate with each other, such as computer to computer or printer to computer. An unmanaged switch does not need to be monitored or configured using external software applications. They are easy to set up and require only cable connections. Unmanaged network switches are ideal for small and medium networks. Managed Switches 9

10 Managed switches can be modified to suit the functionality of a particular network. They are managed by an embedded simple network management protocol (SNMP), secure shell or via a serial console. There are two types of managed switches: smart switches and enterprise managed switches. Smart switches fall between unmanaged and managed switches. They offer most of the features of managed switches without their cost or complexity. A smart switch is able to configure virtual LANs, ports and set up trucking. Smart switches are ideally used in fast LANs, which are those that support gigabit data transfer. Enterprise managed switches are also called fully managed switches. They have a wide range of management features, including a web interface, SNMP agent and command-line interface. Additional features include the ability to restore, backup, modify and display configurations. They have more features than traditional managed and unmanaged switches and are generally more expensive. They are found in large enterprises, which are comprised of a large number of connections and nodes. Router Routers connect networks. A router links computers to the Internet, so users can share the connection (NAT). A router acts as a dispatcher, choosing the best path for information to travel so it's received quickly. The router is the only device that sees every message sent by any computer on either of the company's networks. The Router looks at the IP Address to route the packets. All but the most basic of networks require devices to provide connectivity and functionality. Understanding how these networking devices operate and identifying the functions they perform are essential skills for any network administrator. ARP (Address Resolution Protocol): In computer networking, the Address Resolution Protocol (ARP) is the method for finding a host's hardware address when only its network layer address is known. ARP is primarily used to translate IP addresses to Ethernet MAC addresses. ARP is used in four cases of two hosts communicating: When two hosts are on the same network and one desires to send a packet to the other When two hosts are on different networks and must use a gateway/router to reach the other host. When a router needs to forward a packet for one host through another router. When a router needs to forward a packet from one host to the destination host on the same network Reverse Address Resolution Protocol (RARP) is a network layer protocol used to resolve an IP address from a given hardware address (such as an Ethernet address). It has been rendered obsolete by BOOTP and the more modern DHCP, which both support a much greater feature set than RARP. RARP is the complement of ARP 10

11 IP Addressing and sub netting: Any given host or interface on a network has a logical Unique ID called as IP (Internet Protocol) Address, IPV4 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: Address The unique number ID assigned to one host or interface in a network. Subnet A portion of a network sharing a particular subnet addresses. Subnet mask A 32-bit combination used to describe which portion of an address refers to the subnet and which part refers to the host. 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. Subnet mask is used in conjunction with the ANDING process to know whether the source computer needs to send the packet within the network or to the default gateway. IP Addresses are categorized in to Classes Class 1st Octet Decimal Range 1st Octet High Order Bits Network/Host ID (N=Network, H=Host) Default Subnet Mask Number of Networks Hosts per Network (Usable Addresses) A 1 126* 0 N.H.H.H (27 2) 16,777,214 (224 2) B N.N.H.H C N.N.N.H D Reserved for Multicasting E Experimental; used for research 16,382 (214 2) 2,097,150 (221 2) 65,534 (216 2) 254 (28 2) Note: Class A addresses to cannot be used and is reserved for loopback and diagnostic functions. 11

12 Subnet Masks: A network mask helps you know which portion of the address identifies the network and which portion of the address identifies the node. Class A, B, and C networks have default masks, also known as natural masks, as shown here: Default subnet masks: Class A Class B Class C Private IP Address Class Private Networks Subnet Mask Address Range A B C Subnetting: Subnetting allows you to create multiple logical networks that exist within a single Class A, B, or C network. If you do not subnet, you are only able to use one network from your Class A, B, or C network, which is unrealistic. Each data link on a network must have a unique network ID, with every node on that link being a member of the same network. If you break a major network (Class A, B, or C) into smaller subnetworks, it allows you to create a network of interconnecting subnetworks. Each data link on this network would then have a unique network/subnetwork ID. Any device, or gateway, connecting n networks/subnetworks has n distinct IP addresses, one for each network / subnetwork that it interconnects. In order to subnet a network, extend the natural mask using some of the bits from the host ID portion of the address to create a subnetwork ID. For example, given a Class C network of which has a natural mask of , you can create subnets in this manner: sub ---- By extending the mask to be , you have taken three bits (indicated by "sub") from the original host portion of the address and used them to make subnets. With these three bits, it is possible to create eight subnets. With the remaining five host ID bits, each subnet can have up to 32 host addresses, 30 of which can actually be assigned to a device since host ids of all zeros or all ones are not allowed (it is very important to remember this). So, with this in mind, these subnets have been created host address range 1 to host address range 33 to host address range 65 to host address range 97 to host address range 129 to host address range 161 to host address range 193 to host address range 225 to 254 No of subnetworks can be calculated with the Formula 2 to the power of x where x is no bits added to the network 12

13 Routing: Routing is the process of moving packets through an internetwork, such as the Internet. Routing actually consists of two separate, but related, tasks: 1. Define paths for the transmission of packets through an internetwork. 2. Forwarding packets based upon the defined paths Static vs. Dynamic Routing Routing can be accomplished by manually entering the information necessary for packets to reach any part of the internetwork into each router. This is called STATIC ROUTING. Static routing works reasonably well for very small networks, but does not scale well. When using static routing, the routing tables on each router must be updated each time the network topology changes such as when a network link fails. In most networks, routing is managed automatically by dynamic routing. In dynamic routing, routing protocols create and maintain the routing tables automatically. Dynamic routing responds much more quickly to network changes (and network failures) than static routing. Cabling: A network cabling that connects a computer to a network device. For example, straight through cables are cables that connect a computer to a network hub, network switch, and network routers. These are the standard network cables you would find at the store, unless labeled as a cross-over cable. To create your own network cables you will first need the equipment we have listed below. 1) Cat5, Cat5e, Cat6, or Cat7 cable - This cabling can be purchased in large spindles at stores that specialize in cabling. Cat5 cabling is the most commonly used cable used today for networks 2) RJ-45 connectors - These connectors can be purchased at most electronic stores and computer stores and usually come in bulk packages. It's always a good idea to get more than you expect you will need. 3) Crimping tool - These tools are often purchased at electronic stores such as radio shack. To create a network cable you will need a crimper that is capable of crimping a RJ-45 cable (not just a RJ-11 cable, which looks similar to a RJ-45). 4) Wire stripper / Knife - If you plan on making several network cables you should also consider getting a wire stripper cable of stripping Cat5, Cat6, or your cable of choice. If you do not plan on creating many network cables a knife will suffice. For simplicity and to prevent potential issues we recommend a wire stripper. Once you have the necessary equipment needed to create your own network cables you need to determine the network cable you wish to create. There are two major network cables: a straight through cable and a crossover cable. Below are some examples of what cable is used for each of the examples. Straight Through Wired Cables: Straight Through refers to cables that have the pin assignments on each end of the cable. In other words, Pin 1 connector A goes to Pin 1 on connector B, Pin 2 to Pin 2 etc. Straight-Through wired cables are most commonly used to connect a host to client. When we talk about cat5e patch cables, the 13

14 Straight-Through wired cat5e patch cable is used to connect computers, printers, and other network client devices to the router switch or hub (the host device in this instance). Crossover Wired Cables: Crossover wired cables (commonly called crossover cables) are very much like Straight-Through cables with the exception that TX and RX lines are crossed (they are at opposite positions on either end of the cable. Using the 568-B standard as an example below you will see that Pin 1 on connector A goes to Pin 3 on connector B. Pin 2 on connector A goes to Pin 6 on connector B etc. Crossover cables are most commonly used to connect two hosts directly. Examples would be connecting a computer directly to another computer, connecting a switch directly to another switch, or connecting a router to a router. Note: While in the past when connecting two host devices directly a crossover cable was required. Now days most devices have auto sensing technology that detects the cable and device and crosses pairs when needed. Rollover Wired Cables: Rollover wired cables most commonly called rollover cables, have opposite Pin assignments on each end of the cable or in other words it is "rolled over". Pin 1 of connector A would be connected to Pin 8 of connector B. Pin 2 of connector A would be connected to Pin 7 of connector B and so on. Rollover cables, sometimes referred to as Yost cables are most commonly used to connect to a devices console port to make programming changes to the device. Unlike crossover and straight-wired cables, rollover cables are not intended to carry data but instead create an interface with the device. 14

15 Network Troubleshooting: Any troubleshooting task is basically a series of steps. The actual steps you take will vary from problem to problem. Later steps in the process may depend on the results from earlier steps. Still, it is worth thinking about and mapping out the steps since doing this will help you remain focused and avoid needless steps. There are 7 steps for Network Troubleshooting, and they are Identify the problem Establish a theory Test the theory Establish a plan of action Implement the solution or escalate Verify full system functionality Document finding, actions and outcomes Ping: Ping is part of ICMP (Internet Control Message Protocol) which is used to troubleshoot TCP/IP networks. So, ping is basically a command that allows you to check whether the host is alive or not. To ping a particular host the syntax is (at command prompt)..c :/> ping hostname.com Example: C :/> ping Netstat:It displays protocol statistics and current TCP/IP network connections. i.e. local address, remote address, port numbers, etc. 15

16 The syntax is (at command prompt) C :/> netstat n Traceroute: Traceroute is a command, which can show you the path a packet of information takes from your computer to one you specify. It will list all the routers it passes through until it reaches its destination, or fails to and is discarded. In addition to this, it will tell you how long each 'hop' from router to router takes. The syntax is (at command prompt)..c :/> tracert hostname.com Ethereal:Ethereal is a freeware sniffing tool that can be used to view packets on the network. This tool is especially useful to detect any intrusion attempts. It can be used in Linux, UNIX and Windows operating systems. Shows the packets that have been captured during the time. Shows the select packet in 1 in more details. Every option in the 2 window is in expand/collapse form. If expanded more details of the packet can be observed. Shows the actual packet captured. 16