CHAPTER 2: Network Media 96 C. Use 10BaseT cabling in each of the buildings, and connect the two buildings together using 10Base5 cabling. D. Use 100BaseFX cabling in each of the buildings, and connect the two buildings together using 10BaseT cabling. Your network uses 100BaseFX so that data can be transferred at 9. higher speeds and up to distances of 400 m. During transmission, data can travel in both directions, but only in one direction at a given time. Which of the following transmission methods is used? A. Simplex B. FireWire C. Half-Duplex D. Full Duplex Examine the illustration shown in Figure 2.13. Your network uses 10. UTP cabling in a star topology. Which of the following types of connectors is being used? A. RJ-45 B. BNC C. ST D. SC You are the Network11. technician assigned to an enterprise network looking to install a high-speed backbone. You want to implement Gigabit Ethernet. Which connectors could you use in such a network? (Choose one.) FIGURE 2.13 Self Test 97 A. RJ-11 B. RG 58 C. SC D. BNC As a Network technician for 123 LLC, you are asked by your 12. CIO about the access method of Gigabit Ethernet. Which of the following access methods does Gigabit Ethernet use? A. FDDI B. CSMA/CD C. CSMA/CA D. Token passing A new technician for 123 Corp plans out the maximum length of a 13. Gigabit Ethernet segment using MMF optic cable is. What is the cor- rect distance? (Choose only one) A. 100 m B. 125 m C. 550 m D. 10 km You are the network engineer assigned to implement a new 14. 100 Mbps network connection. You need to select the correct cabling, as well as the correct standard. From the selections below, choose which 100 Mbps networking standard makes use of only two pairs of a Category 5 UTP cable. A. 10BaseT B. 100BaseFL C. 100BaseTX D. 100BroadT4 You work as a network technician for 123 LLC. You need to check 15. the electrical signals being sent from the NIC port out on the cable. Which device would you use to complete this test? (Choose one.) A. A wire map B. A fox and hound C. A crossover cable D. A hardware loopback CHAPTER 2: Network Media 98 SELF TEST QUICK ANSWER KEY B1. A2. B3. D4. B5. B6. D7. C8. C9. A10. C11. B12. C13. C14. D15. 99 CHAPTER 3 EXAM OBJECTIVES IN THIS CHAPTER NETWORK DEVICES 99 INTRODUCTION A network is composed of many different devices; some perform a single function and others perform a variety of functions, from routing data to applying security filters. As networking devices become more complex, they also become more versatile, in that they may be able to perform multiple roles that previously could only be carried out by individual devices. Some network devices are complex enough to warrant their own operating systems for inten- sive and detailed configuration. In some cases, these operating systems can be switched out, substituted, or used to configure the device to perform roles traditionally carried out by other devices. For example, a Layer 3 switch might be configured to combine both switching and routing functions. This coming together of technology within one device is called convergence. In this chapter we will briefly discuss convergence, and we will look at the most common network devices in use today on small and large networks, including the Internet. These devices range from the very simple (such as an active hub, which simply repeats and sends out signals to all ports) to the more complex devices, such as a firewall, which is responsible for controlling traffic and applying security features. NETWORK DEVICES Network devices are components of a network that are required if the network is to grow, function, or provide certain functionality. There are a number of devices that fall into this category, including routers, switches, Network Devices CHAPTER 3: Network Devices 100 and other devices that we’ve mentioned briefly in previous chapters. These network devices provide functionality such as connectivity to physical media, security features, and the ability to connect to resources outside of the local area network (LAN). Before we discuss the current state of networking and the available devices, let’s take a look at how the current devices evolved. Historical Network Devices As we discussed in Chapter 1, networks have been around for decades, so it follows that some devices have been around longer than others. As we’ll see in the sections that follow, although some devices are as useful today as when they were initially introduced, others have become obsolete and are rarely used on today’s networks. In discussing these devices, we’ll tell you about their purpose, features, and functions on a network. HEAD OF THE CLASS… OSI and Network Devices Network devices can be mapped to the Open Systems Interconnect (OSI) networking model. OSI is a group of standards that provides a logical structure for net- work operations and contains seven layers, which from the highest to lowest are as follows: application, pre- sentation, session, transport, network, data link, and physical. Network communication starts at the applica- tion layer of the OSI model and works its way down through the layers step by step to the physical layer. The information then passes along the cable to the receiving computer, which starts the information at the physical layer. From there it steps back up the OSI layers to the application layer where the receiving computer finalizes the processing and sends back an acknowledgement if needed. Then the whole process starts over. Table 3.1 shows the devices mapped to the OSI layers at which they operate. Table 3.1 Mapping of Network Devices to the OSI Model OSI Layer Devices Application Gateway Presentation Gateway Session Gateway Transport Gateway Network Router, multilayer or Layer 3 switches, gateway Data Link NIC, bridge, Layer 2 switches, access point, gateway Physical Hub, MAU, repeater, gateway Network Devices 101 Hubs Although hubs have been around since the early days of networking, they continue to be one of the most commonly used connection-based net- work components. Especially now that home networks are growing and more small office home offices (SOHOs) are emerging, hubs are becom- ing a common household item. Some homes are even built with a plan for a centralized wiring system, Internet access, routers, and hubs all included. Hubs are predecessors of switches, which we’ll discuss later in this chapter, and are central locations for connecting network cabling. Multi- ple cables connect into the hub, providing a method for data to be passed from one cable to another. This is also why switches are sometimes referred to as switching hubs, though that terminology is not commonly used today. As we discussed in Chapter 1, a star topology uses a hub to connect workstations, servers, and other devices. As shown in Figure 3.1, you can easily remember the layout of a hub if you think of a wheel and picture how the spokes go to the hub of the wheel. Each spoke is a connection and the hub of the wheel is the hub of the network where all the cables come together. Because all of the connections concentrate in the center, the hub is also called a concentrator. Each of the cables that extends to the hub from computers and other network devices is plugged into its own port on the hub. The port pro- vides an interface between the cable and the hub. For example, because star topologies may use unshielded twisted-pair (UTP) cable, UTP is a common cable type that is used with hubs. The RJ-45 connector of the cable is plugged into a port on the hub. When data is sent from a computer, it is carried along the cable to the port that the RJ-45 connector is plugged into. The hub then takes this data and passes it to the other ports, allowing the data to travel along the other cables to workstations and devices that are attached to it. The number of ports on a hub will vary, but generally four or more are provided. Many hubs provide 24 or 28 ports and can be attached together (or more commonly referred to as uplinked FIGURE 3.1 Hubs Are Used in Star Topologies. CHAPTER 3: Network Devices 102 or cascaded together) to provide connectivity to even more computers or network devices. There are rules, of course; when working with hubs, you should always apply the 5-4-3 rule, which states that you can only con- nect a total of 5 segments linked together via 4 hubs and only 3 of those segments can be populated with network hosts such as PCs or printers. Breaking rules of this kind could lead to a degradation of performance and possible problems. The two main types of hubs are passive and active. A switching hub is actually a type of switch that behaves like a hub. Passive Hubs In discussing hubs to this point, we have essentially been talking about pas- sive hubs. A passive hub provides basic features of moving data from one port to another. Its function is simply to receive data from one port of the hub and send it out to the other ports. For example, an 8-port hub receives data from port 3 and then resends that data to ports 1, 2, 4, 5, 6, 7, and 8. It is as simple as that. A passive hub contains no power source or electrical components. There is no signal processing. It simply attaches the ports internally and enables communication to flow through the network. Active Hubs An active hub provides the same functionality that a passive hub does, with an additional feature. Active hubs repeat (regenerate) the data while resend- ing it to all of its ports. By using active hubs you can increase the length of your network beyond regular cable length limits. For example, UTP Category 5 cabling can be run a maximum of 100 m. With an active hub, you can run Category 5 UTP 100 m on each side of the hub so that your cable now runs a length of 200 m in total. Exam Warning Hubs broadcast traffic on every single port. Because hubs only operate at the physi- cal layer, they are deemed unintelligent. A hub is simple by design; a signal comes in from a connected PC, and the hub just sends that signal out to every port that it knows. For example, suppose an 8-port hub has eight PCs attached. If PC 1 sends an e-mail to PC 2, that transmission will go to all the eight PCs. The data, of course, will get to its destination, but all six of the uninvolved PCs are interrupted because each has to examine the data to determine if it is the recipient. This process takes time, and if you multiply this over the traffic of a normal large-scale enterprise network, it’s easy to see why hubs are typically limited to small networks. Network Devices 103 An active hub has a power source and built-in repeaters to boost the signal. There are extra electronics built into an active hub that allow for signal regeneration, which is how the incoming data on one port is repeated to the other ports. Because the signal is repeated in this way to the other ports, an active hub is also called a multiport repeater. Switching Hubs Although active and passive hubs will pass data to every other port on the hub, a switching hub will only send data to its intended port. Switching hubs are also referred to as intelligent hubs, as they can determine which port will get the data to its proper destination. The fact is, however, that even though it is referred to as a switching hub, these are the features of another device called a switch (which we’ll discuss later in this chapter). Although this term may be used in the real world to refer to a switch, for the Network+ exam it’s best to keep the components separate in your mind. A switch is a switch, and a hub is a hub. Repeaters A repeater is a device that is rarely seen on networks today, as its features are typically incorporated into other devices, such as active and switching hubs. The repeater will take a signal that may be weakening and regenerate it to its original strength. In doing so, it actually recreates the signal, making it the same strength that it was when it left the sending workstation. To help you understand a repeater, imagine that you are with a friend and both of you are standing at opposite ends of a street. If you shouted some- thing to your friend, the sound would fade over a distance. If someone stood between the two of you, however, and repeated your message, then it would be repeated strong and loud, allowing your friend to hear it. A repeater works Test Day Tip The Network+ exam includes questions that deal with active hubs. Passive hubs aren’t covered on the current version of the exam. This information is included for completeness. Exam Warning Hubs operate at the physical layer of the OSI model (also known as Layer 1). Hubs are designed to simply forward data from one port of the hub to another, so they don’t use upper-layer protocols such as Internet Protocol (IP), Internetwork Packet Exchange (IPX), or Media Access Control (MAC) addressing to ensure that the data reaches its intended destination. CHAPTER 3: Network Devices 104 in a similar fashion by repeating the data so it’s in its original, strong form preventing corruption as it weakens over distance. Historically, repeaters were first created to fix a problem. Cables had length limitations, which were solved by connecting a repeater to two cable segments to extend the range beyond the regular distance limit. Repeaters were commonly used on Ethernet networks, such as those using UTP or coaxial cable, and provided networks with the ability to extend cable seg- ments. 10BaseT limitations are 100 m or approximately 328 feet. Thickwire (also known as 10Base5 or Thicknet) can normally transmit a distance of 500 m, whereas thinwire (also known as 10Base2 or Thinnet) can normally transmit a distance of 185 m. By putting a repeater between these segments, the distance that data can travel can be doubled. Remember, when using repeaters, greater lengths of cabling were allowed when planning a cabling scheme. Bridges A bridge is a network connectivity device that connects two different net- works and makes them appear to be one network. It can connect two differ- ent LANs, or allow a larger LAN to be segmented into two smaller halves. The bridge filters local traffic between the two networks and copies all other traffic to the other side of the bridge. Bridges are intelligent devices and have the ability to forward packets of data based on MAC addresses. A bridge can look at a packet of data and determine the source and destination involved in the transfer of packets. It will read the specific physical address of a packet on one network segment and then decide to filter out the packet or forward it to another segment. A bridge is another device that has largely become a thing of the past. Although bridges were a common component of older networks, their fea- tures are now typically incorporated into switches. One benefit of a switch over a bridge is that a bridge only has two ports typically, one for each seg- ment that it is connecting. Switches may have many ports, and as we’ve already seen, incorporate features that were previously found in other devices, such as hubs. Note Unlike previous versions of the Network+ exam, repeaters are no longer directly tested on the exam. The function of a repeater is to regenerate data so that it can be passed further than the maximum distance of a cable segment. The ability to regenerate data and perform this function is now found incorporated in other network devices, such as hubs and switches. Network Devices 105 Network Segmentation A bridge is a simple way to accomplish network segmentation. Placing a bridge between two different segments of the network decreases the amount of traffic on each of the local networks. Although this does accomplish network segmentation, most network administrators opt to use routers or switches, which are discussed later in the chapter. Bridges segment the network by MAC addresses. When one of the work- stations connected to one network has to transmit a packet, the packet is copied across the bridge as long as the packet’s destination is not on its origi- nating network segment. A bridge uses a bridging table to calculate which MAC addresses are on which network. The MAC address uniquely identifies computers and other devices on a network, just as the full address of your house uniquely identifies its location. Multistation Access Units Multistation access units (also known as MAUs or MSAUs) are used to connect workstations on a Token Ring network. Sometimes, an MAU is referred to as a hub on the Network+ exam, but it shouldn’t be confused with the active and passive hubs we discussed earlier, which are used on Ethernet networks. The features of an MAU are different from those of a standard hub. An MAU typically has eight or more ports that provide connections for workstations and other network devices on a Token Ring network. It is also generally nonpowered, although some have been produced that are powered with lights to indicate connectivity and activity. An MAU is not something you will commonly find on newer networks simply because newer networks generally are installed as Ethernet, more typically Fast Ethernet or Gigabit Ethernet. MAUs are used with Token Ring networks, which are present in today’s environments, but are not as prevalent as Ethernet. Test Day Tip The Network+ exam frequently uses the term bridging and does refer to the actual device quite often. Make sure that you understand the concepts of bridging that it will connect up to two different network segments. Exam Warning Bridges operate at the data link layer of the OSI model and use physical addressing to join several networks into a single network efficiently. . 2.13 Self Test 97 A. RJ-11 B. RG 58 C. SC D. BNC As a Network technician for 123 LLC, you are asked by your 12. CIO about the access method of Gigabit Ethernet. Which of the following access. technician for 123 Corp plans out the maximum length of a 13. Gigabit Ethernet segment using MMF optic cable is. What is the cor- rect distance? (Choose only one) A. 100 m B. 125 m C. 550. cable. A. 10BaseT B. 100BaseFL C. 100BaseTX D. 100BroadT4 You work as a network technician for 123 LLC. You need to check 15. the electrical signals being sent from the NIC port out on the cable.