Networking.docx

Wiring Standards Twisted-pair cables are unique in today’s network environment in that they use multiple physical wires. Those eight wires need to be in the right places in the RJ-45 connector or it’s very likely that the cable will not work properly. To ensure consistency in the industry, two stand...

Wiring Standards Twisted-pair cables are unique in today’s network environment in that they use multiple physical wires. Those eight wires need to be in the right places in the RJ-45 connector or it’s very likely that the cable will not work properly. To ensure consistency in the industry, two standards have been developed: 568A and 568B. Older implementations using UTP used only two pairs of wires, and those two pairs were matched to pins 1, 2, 3, and 6 in the connector. Newer applications such as Voice over IP and Gigabit Ethernet use all four pairs of wires, so you need to make sure that they’re all where they’re supposed to be. If you’re creating a regular network patch cable to connect a computer to a hub or switch, both sides need to have the same pinout. For that, follow either the 568A standard shown in Figure 6.24 or the 568B standard shown in Figure 6.25. Although there are no differences in terms of how the standards perform, some companies prefer one to the other. Figure 6.24 568A standard If you are going to create a cable to connect a computer to another computer directly, or you’re going to make a connection from hub to hub, switch to switch, hub to switch, or a computer directly to a router, then you need what’s called a crossover cable. In a crossover cable, pin 1 to pin 3 and pin 2 to pin 6 are crossed on one side of the cable only. This is to get the “send” pins matched up with the “receive” pins on the other side, and vice versa. For easier visualization, look at Figure 6.25. 346 Figure 6.25 568B standard The key thing to remember is that a patch (straight-through) cable is the same on both ends. A crossover cable is different on each end. You should know the order of the colors for both standards. Fiber-Optic Cable Fiber-optic cabling has been called one of the best advances in cabling. It consists of a thin, flexible glass or plastic fiber surrounded by a rubberized outer coating (see Figure 6.26). It provides transmission speeds from 100 Mbps to 10 Gbps and a maximum distance of several miles. Because it uses pulses of light instead of electric voltages to transmit data, it is immune to electrical interference and to wiretapping. Figure 6.26 Fiber-optic cable Optical fiber cable by Buy_on_turbosquid_optical.jpg: Cable master derivative work: Srleffler (talk) - Buy_on_turbosquid_optical.jpg http://commons.wikimedia.org/wiki/File:Optical_fiber_cable.jpg#/media/File:Optical_fiber_cable.jpg Fiber-optic cable is still not as popular as UTP for local area networks, however, because of its high cost of installation. Fiber-optic cabling is great for networks that need extremely fast transmission rates or transmissions over long distances or in networks that have had problems with electrical interference in the past. Fiber is also becoming more common as347backbones to the telecommunication system, and in many places fiber-optic cables can be used to deliver high-speed Internet connections to businesses and homes. We’ll talk more about this in Chapter 8. Fiber-Optic Cable Specifications Fiber-optic cable comes in two varieties: single-mode or multimode. The term mode refers to the bundles of light that enter the fiber-optic cable. Single-mode fiber (SMF) cable uses only a single mode (or path) of light to propagate through the fiber cable, whereas multimode fiber (MMF) allows multiple modes of light to propagate simultaneously. In multimode fiber-optic cable, the light bounces off the cable walls as it travels through the cable, which causes the signal to weaken more quickly. Multimode fiber is most often used as horizontal cable. It permits multiple modes of light to propagate through the cable, which shortens cable distances but delivers more available bandwidth. Devices that use MMF cable typically use light-emitting diodes (LEDs) to generate the light that travels through the cable; however, lasers with multimode fiber-optic cable are now being used in higher-bandwidth network devices, such as Gigabit Ethernet. MMF can transmit up to 10 Gbps for up to 550 meters (1,804 feet, or just over one-third of a mile), depending on the standard used. Single-mode fiber cable is commonly used as backbone cabling. It is also usually the cable type used in phone systems. Light travels through single-mode fiber-optic cable using only a single mode, meaning that it travels straight down the fiber and does not bounce off the cable walls. Because only a single mode of light travels through the cable, single-mode fiber-optic cable supports lower bandwidth at longer distances than does multimode fiber-optic cable. Devices that use single-mode fiber-optic cable typically use lasers to generate the light that travels through the cable. SMF can transmit up to 10 Gbps for up to 40 kilometers (25.85 miles), depending on the standard used. We have talked about several different types of cables, and it’s possible that you will be asked to know maximum distances and transmission speeds on the A+ exam. Table 6.3 summarizes the most common cable types, the specifications with which they are used, and their characteristics. 348 Table 6.3 Common cable types and characteristics Cable type Ethernet Specification Maximum Speed Maximum Distance Notes RG-6 coax * * 304 meters Digital cable/satellite television RG-59 coax * * 228 meters Analog cable TV CAT-5 UTP or STP 100BaseT 100 Mbps 100 meters 100 Mbps and less use two pairs of wires. CAT-5e UTP 1000BaseT 1 Gbps 100 meters 1 Gbps and higher use four pairs of wires. CAT-6 UTP 10GBaseT 10 Gbps 55 meters Can support 1 Gbps up to 100 meters CAT-6a UTP 10GBaseT 10 Gbps 100 meters CAT-7 UTP 10GBaseT 10 Gbps 100 meters Every wire pair is individually shielded. MMF fiber 1000BaseLX or 1000BaseSX 1 Gbps 550 meters For fiber, maximum length depends on fiber size and quality. MMF fiber 10GBaseSR or 10GBaseSW 10 Gbps 300 meters SMF fiber 10GBaseER or 10GBaseEW 10 Gbps 40 kilometers *RG-6 and RG-59 coax cables can be used with many different specifications, and the maximum speed depends on cable quality and specification. Fiber-Optic Connector Types There are literally dozens of fiber-optic connectors out there because it seemed that every producer wanted its proprietary design to become “the standard.” Three of the most commonly used ones are ST, SC, and LC. The straight tip (ST) fiber-optic connector, developed by AT&T, is probably the most widely used fiber-optic connector. It uses a BNC-style attachment mechanism that makes connections and disconnections fairly easy. The ease of use of the ST is one of the attributes that make this connector so popular. Figure 6.27 shows ST connectors. Figure 6.27 ST connectors 349 The subscriber connector (SC), also sometimes known as a square connector, is shown in Figure 6.28. SCs are latched connectors, making it virtually impossible for you to pull out the connector without releasing its latch, usually by pressing a button or release. SCs work with either single-mode or multimode optical fibers. They aren’t as popular as ST connectors for LAN connections. Figure 6.28 A sample SC The last type of connector with which you need to be familiar is the local connector (LC), which was developed by Lucent Technologies. It is a mini form factor (MFF) connector, especially popular for use with Fibre-Channel adapters, fast storage area networks, and Gigabit Ethernet adapters (see Figure 6.29). Figure 6.29 LC fiber connector The prices of network cables differ dramatically between copper and fiber cables. Exercise 6.1 asks you to investigate the difference for yourself. EXERCISE 6.1 Pricing Network Cables Visit a major electronics retailer website (such as www.frys.com or an online retailer of your choice). Search for a CAT-6 patch cable. Price the difference between a 7-foot, 25-foot, and 50-foot cable. 350 Search for the same lengths of CAT-7 patch cables. Note the price difference. (At the time of writing, CAT-7 cables were about twice as expensive as CAT-6 cables.) Search for fiber-optic cables. Notice, first, that most of them are much shorter in length than commercially available UTP cables. What is the price difference? Do you notice price differences between fiber-optic cables with different types of connectors? Networking Components Network cabling can link one computer to another, but most networks are far grander in scale than two simple machines. There are a variety of networking devices that provide connectivity to the network, make the network bigger, and offer auxiliary services to end users. In the following sections, we’re going to classify additional networking components into two broad categories: connectivity devices and auxiliary devices. Connectivity Devices We all know that if you want to be part of a computer network, you need to attach to that network somehow. Using network cables is one way to accomplish this, but not everyone is in a position to just plug a cable in and go. In addition, if you want to grow your network beyond a few simple connections, you need to use a special class of networking devices known as connectivity devices. These devices allow communications to break the boundaries of local networks and really provide the backbone for nearly all computer networks, regardless of size. There are several categories of connectivity devices. These connectivity devices make it possible for users to connect to networks and to lengthen networks to almost unlimited distances. We will now discuss the most important and frequently used connectivity devices. Modems If you want to connect to a network or the Internet using plain old phone lines and a dial-up connection, a modem is the device you’ll need. Modems got their name because they modulate and demodulate (mo-dem) digital signals that computers use into analog signals that can be passed over telephone lines. In the early to mid-1990s, modems were practically the only device available to get onto the Internet. Many companies also used them to allow users who were not in the office to dial into the local network. While modems did provide flexibility, you needed to be near a phone line, and speed was an issue. The fastest modems transferred data at 56 Kbps. At the time that felt lightning351quick, but fortunately our species has moved well beyond that technology. It’s horrifically slow by today’s standards and therefore rarely used. Cable/DSL Modems The traditional modem is essentially obsolete—most homes and many businesses now access the Internet through the use of a cable modem or digital subscriber line (DSL) modem. The primary difference between the two is the infrastructure they connect to. Cable modems use television cable lines, and DSL modems use telephone lines. Both cable and DSL modems are digital, and therefore aren’t technically modems because they don’t modulate and demodulate analog signals. We’ll cover cable Internet and DSL technologies in more detail in Chapter 8. Access Points Technically speaking, an access point is any point that allows a user on to a network. The term is commonly used in reference to a wireless access point, which lets users connect to your network via an 802.11 technology. We’ll get deeper into wireless access points and how to configure them in Chapter 8. Repeaters and Extenders A repeater, or extender, is a small, powered device that receives a signal, amplifies it, and sends it on its way. The whole purpose of a repeater is to extend the functional distance of a cable run. For example, you know that UTP is limited to 100 meters, but what if you need to make a cable run that is 160 meters long? (One answer could be to use fiber, but pretend that’s not an option.) You could run two lengths of cable with a repeater in the center, and it would work. Repeaters and extenders work at the Physical layer (Layer 1) of the OSI model. They don’t examine the data or make any changes to it—they just take what they receive and send it along its merry way. Hubs A hub is a device used to link several computers together. Hubs are very simple devices that possess no real intelligence. They simply repeat any signal that comes in on one port and copy it to the other ports (a process that is also called broadcasting). You’ll sometimes hear them referred to as multiport repeaters. They work at Layer 1 of the OSI model, just as repeaters do. There are two types of hubs: active and passive. Passive hubs connect all ports together electrically but do not have their own power source. Active hubs use electronics to amplify and clean up the signal before it is broadcast to the other ports. Active hubs can therefore be used to extend the length of a network, whereas passive hubs cannot. Patch Panels A patch panel is essentially a large hub that is rack mounted. It houses multiple cable connections but possesses no network intelligence. Its sole purpose is to connect cables together. Short patch cables are used to plug into the front-panel connectors, and there are longer, more permanent cables on the back. Figure 6.30 shows three rack-mounted devices.352The top one is a 24-port patch panel. Underneath that is a 24-port switch, and then a Dell server is shown. Figure 6.30 A patch panel, switch, and server Bridges Bridges operate in the Data Link layer (Layer 2) of the OSI model. They join similar topologies, and they are used to divide network segments into multiple collision domains. Bridges isolate network traffic, preventing unwanted traffic from entering a segment when there are no recipients on that segment. For example, with 100 people on one Ethernet segment, performance will be mediocre because of the design of Ethernet and the number of workstations that are fighting to transmit. If you use a bridge to divide the segment into two segments of 50 workstations each, the traffic will be much lower on either side, and performance will improve. Bridges are not able to distinguish one protocol from another because higher levels of the OSI model are not available to them. If a bridge is aware of the destination MAC address, it can forward packets to the correct segment; otherwise, it forwards the packets to all segments.  Because bridges work at the Data Link layer, they are aware of only hardware (MAC) addresses. They are not aware of and do not deal with IP addresses. Bridges are more intelligent than repeaters, but they are unable to move data across multiple networks simultaneously. 353 The main disadvantage of bridges is that they forward broadcast packets. Broadcasts are addressed to all computers, so the bridge just does its job and forwards the packets. Bridges also cannot perform intelligent path selection, meaning that the path from the sender to the destination will always be the same regardless of network conditions. To stop broadcasts or perform intelligent path selection, you need a router. Switches Switches work at Layer 2, as do bridges, and they provide centralized connectivity, just like hubs. They often look similar to hubs, so it’s easy to confuse them. There are big performance differences, though. Hubs pass along all traffic, but switches examine the Layer 2 header of the incoming packet and forward it properly to the right port and only that port. This greatly reduces overhead and thus improves performance because there is essentially a virtual connection between sender and receiver. The only downside is that switches forward broadcasts because they are addressed to everyone.  If it helps you to remember their functions, a hub is essentially a multiport repeater, whereas a switch functions like a multiport bridge and, in some cases, a multiport router. Switches come in two varieties: unmanaged and managed. We’ve already explained the functionality of an unmanaged switch—it connects two or more computers, and passes along all traffic sent to a MAC address to its port. A managed switch adds the ability to configure ports, manage traffic, and monitor traffic for issues. For management, the switch will use a network protocol, such as Simple Network Management Protocol (SNMP). (We’ll talk about SNMP in depth in Chapter 7.) Managed switches cost more but provide features such as quality of service (QoS), redundancy, port mirroring, and virtual LANs (VLANs). Here’s a description of each: QoS QoS allows administrators to prioritize certain network traffic by assigning a higher priority to it. Higher priority traffic may come from a specific server or specific application. This is used a lot with Voice over IP (VoIP)—telephone calls over a computer network—to ensure that the voice data gets through and the connection doesn’t sound garbled. Redundancy Redundancy in networking terms means having multiple paths to get data from point A to point B. Administrators can use multiple switches to provide redundant paths, which add a layer of fault tolerance to the network. Managed switches use the Spanning Tree Protocol (STP) to implement redundancy. Port Mirroring This is a troubleshooting feature that is used in conjunction with a network monitor. A port can be configured to mirror another port. When traffic is sent to one, it’s also sent to the mirror. A network monitor attached to the mirrored port can then analyze the traffic, without taking the network or device on the original port offline. VLANs In a virtual LAN (VLAN), computers attached to the same physical switch can be segmented into multiple logical networks. This reduces network traffic on each virtual354LAN, because the traffic is isolated from other virtual LANs. Computers on one virtual LAN can still communicate with those on another virtual LAN, if the switch is configured properly. VLANs can also be completely isolated from each other, adding an additional level of security. Nearly every hub or switch that you will see has one or more status indicator lights on it. If there is a connection to a port of the switch, a light either above the connector or on an LED panel elsewhere on the device will light up. If traffic is crossing the port, the light may flash, or there may be a secondary light that will light up. Many devices can also detect a problem in the connection. If a normal connection produces a green light, a bad connection might produce an amber light. Routers Routers are highly intelligent devices that connect multiple network types and determine the best path for sending data. They can route packets across multiple networks and use routing tables to store network addresses to determine the best destination. Routers operate at the Network layer (Layer 3) of the OSI model. Because of this, they make their decisions on what to do with traffic based on logical addresses, such as an IP address. Routers have a few key functions: They connect multiple networks to each other, which none of the other devices we have discussed do. Routers do not forward broadcasts. (Switches and bridges break up collision domains, whereas routers break up broadcast domains.) Routers are normally used to connect one LAN to another. Typically, when a WAN is set up, at least two routers are used. In the last several years, wireless routers have become all the rage for small business and home networks. They possess all the functionality of routers historically associated with networking, but they are relatively inexpensive. We’ll talk more about these routers in Chapter 8. Auxiliary Devices The devices we just talked about are specialized to provide connectivity. This next group of devices adds in features outside of connectivity that can help network users, specifically by protecting them from malicious attacks, providing network connections over power lines, and providing power over Ethernet cables. Firewall A firewall is a hardware or software solution that serves as your network’s security guard. They’re probably the most important devices on networks that are connected to the Internet. Firewalls can protect you in two ways: They protect your network resources from hackers lurking in the dark corners of the Internet, and they can simultaneously prevent computers on your network from accessing undesirable content on the Internet. At a basic level, firewalls filter packets based on rules defined by the network administrator. 355 Firewalls can be stand-alone “black boxes,” software installed on a server or router, or some combination of hardware and software. Most firewalls will have at least two network connections: one to the Internet, or public side, and one to the internal network, or private side. Some firewalls have a third network port for a second semi-internal network. This port is used to connect servers that can be considered both public and private, such as web and email servers. This intermediary network is known as a demilitarized zone (DMZ).  A DMZ is a semi-public network segment located between a perimeter router and an internal router on your network. It is used for web servers, FTP servers, and email relay servers. Firewalls can be network based, in that they protect a group of computers (or an entire network), or they can be host based. A host-based firewall (such as Windows Firewall) protects only the individual computer on which it’s installed. A firewall is configured to allow only packets that pass specific security restrictions to get through. By default, most firewalls are configured as default deny, which means that all traffic is blocked unless specifically authorized by the administrator. The basic method of configuring firewalls is to use an access control list (ACL). The ACL is the set of rules that determines which traffic gets through the firewall and which traffic is blocked. ACLs are typically configured to block traffic by IP address, port number, domain name, or some combination of all three.  We’ll cover firewalls in more depth in Chapter 8 when we show you how to set up a network. Cloud-Based Network Controller The wireless telecommunication services field is expanding rapidly and includes support for wireless networking in addition to voice communication. One of the key components in this space is called a cloud-based network controller. A cloud-based network controller allows an administrator to remotely manage cloud-capable network infrastructure, including access points, switches, and routers. With these devices, the administrator can create a wireless mesh network (WMN) and manage it from anywhere. To make a WMN work, first purchase hardware that supports cloud-based management. Install the hardware (say, an access point) just like any other access point, and connect devices. Then, with an app on a laptop, tablet, or smartphone, manage and monitor the device. Several companies specialize in this field, including OpenMesh (and the CloudTrax app), Ruckus, Riverbed Xirrus, and Mimosa. Ethernet over Power Occasionally, you will find yourself in a spot where it’s not possible to run cables for a network connection and wireless is a problem as well. For example, perhaps you are installing356a device that only has a wired RJ-45 port but you can’t get a cable to it. Ethernet over Power can help make that connection by using electrical outlets; an adapter is shown in Figure 6.31. Figure 6.31 Ethernet over Power adapter For Ethernet over Power to work, both devices must be on the same electrical circuit, such as would be the case for a house or a small building. To connect the devices, plug both in and then press a button on the side of each device. They will search the electrical circuit for the signal from the other and negotiate the connection. As you can see in Figure 6.31, an Ethernet cable also connects to the device. You can plug that cable into a device directly or into a connectivity device, such as a hub or a switch. Power over Ethernet If you can run an Ethernet signal over power lines, why can’t you run electricity over network cables? As it turns out, you can—with Power over Ethernet (PoE). This technology is extremely useful in situations where you need a wireless access point in a relatively remote location that does not have any power outlets. For it to work, the access point and the device it plugs into (such as a switch) both need to support PoE. In a configuration such as this, the switch would be considered an endspan PoE device, because it’s at the end of the network connection. If the switch in question doesn’t support PoE, you can get a device that sits between the switch and the access point (called a midspan device) whose sole purpose is to supply power via the Ethernet connection. Appropriately, these midspan devices are called Power over Ethernet injectors. 357