Network Components and Devices

This chapter is from the book

CompTIA Network+ N10-007 Exam Cram, 6th Edition

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This chapter is from the book

This chapter is from the book 

CompTIA Network+ N10-007 Exam Cram, 6th Edition

Learn More Buy

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 and are requirements for a Network+ candidate.

This chapter introduces commonly used networking devices. You are not likely to encounter all the devices mentioned in this chapter on the exam, but you can expect to work with at least some of them.

Common Network Devices

• Given a scenario, determine the appropriate placement of networking devices on a network and install/configure them.

The best way to think about this chapter is as a catalog of networking devices. The first half looks at devices that you can commonly find in a network of any substantial size. The devices are discussed in alphabetical order to simplify study and include everything from access points to VPN concentrators.

Firewall

A firewall is a networking device, either hardware or software based, that controls access to your organization’s network. This controlled access is designed to protect data and resources from an outside threat. To do this, firewalls typically are placed at a network’s entry/exit points—for example, between an internal network and the Internet. After it is in place, a firewall can control access into and out of that point.

Although firewalls typically protect internal networks from public networks, they are also used to control access between specific network segments within a network. An example is placing a firewall between the Accounts and Sales departments.

As mentioned, firewalls can be implemented through software or through a dedicated hardware device. Organizations implement software firewalls through network operating systems (NOSs) such as Linux/UNIX, Windows Servers, and Mac OS servers. The firewall is configured on the server to allow or block certain types of network traffic. In small offices and for regular home use, a firewall is commonly installed on the local system and is configured to control traffic. Many third-party firewalls are available.

Hardware firewalls are used in networks of all sizes today. Hardware firewalls are often dedicated network devices that can be implemented with little configuration. They protect all systems behind the firewall from outside sources. Hardware firewalls are readily available and often are combined with other devices today. For example, many broadband routers and wireless access points have firewall functionality built in. In such a case, the router or AP might have a number of ports available to plug systems into.

Router

In a common configuration, routers create larger networks by joining two network segments. A small office/home office (SOHO) router connects a user to the Internet. A SOHO router typically serves 1 to 10 users on the system. A router can be a dedicated hardware device or a computer system with more than one network interface and the appropriate routing software. All modern network operating systems include the functionality to act as a router.

A router derives its name from the fact that it can route data it receives from one network to another. When a router receives a packet of data, it reads the packet’s header to determine the destination address. After the router has determined the address, it looks in its routing table to determine whether it knows how to reach the destination; if it does, it forwards the packet to the next hop on the route. The next hop might be the final destination, or it might be another router. Figure 4.1 shows, in basic terms, how a router works.

FIGURE 4.1 How a router works

A router works at Layer 3 (the network layer) of the OSI model.

Switch

Like hubs, switches are the connectivity points of an Ethernet network. Devices connect to switches via twisted-pair cabling, one cable for each device. The difference between hubs and switches is in how the devices deal with the data they receive. Whereas a hub forwards the data it receives to all the ports on the device, a switch forwards it to only the port that connects to the destination device. It does this by the MAC address of the devices attached to it and then by matching the destination MAC address in the data it receives. Figure 4.2 shows how a switch works. In this case, it has learned the MAC addresses of the devices attached to it; when the workstation sends a message intended for another workstation, it forwards the message on and ignores all the other workstations.

FIGURE 4.2 How a switch works

By forwarding data to only the connection that should receive it, the switch can greatly improve network performance. By creating a direct path between two devices and controlling their communication, the switch can greatly reduce the traffic on the network and therefore the number of collisions. As you might recall, collisions occur on Ethernet networks when two devices attempt to transmit at the same time. In addition, the lack of collisions enables switches to communicate with devices in full-duplex mode. In a full-duplex configuration, devices can send data to and receive data from the switch at the same time. Contrast this with half-duplex communication, in which communication can occur in only one direction at a time. Full-duplex transmission speeds are double that of a standard half-duplex connection. So, a 100 Mbps connection becomes 200 Mbps, and a 1000 Mbps connection becomes 2000 Mbps, and so on.

The net result of these measures is that switches can offer significant performance improvements over hub-based networks, particularly when network use is high.

Irrespective of whether a connection is at full or half duplex, the method of switching dictates how the switch deals with the data it receives. The following is a brief explanation of each method:

• Cut-through: In a cut-through switching environment, the packet begins to be forwarded as soon as it is received. This method is fast, but it creates the possibility of errors being propagated through the network because no error checking occurs.

• Store-and-forward: Unlike cut-through, in a store-and-forward switching environment, the entire packet is received and error-checked before being forwarded. The upside of this method is that errors are not propagated through the network. The downside is that the error-checking process takes a relatively long time, and store-and-forward switching is considerably slower as a result.

• Fragment-free: To take advantage of the error checking of store-and-forward switching, but still offer performance levels nearing that of cut-through switching, fragment-free switching can be used. In a fragment-free switching environment, enough of the packet is read so that the switch can determine whether the packet has been involved in a collision. As soon as the collision status has been determined, the packet is forwarded.

Hub and Switch Cabling

In addition to acting as a connection point for network devices, hubs and switches can be connected to create larger networks. This connection can be achieved through standard ports with a special cable or by using special ports with a standard cable.

The ports on a hub to which computer systems are attached are called Medium-Dependent Interface Crossed (MDI-X). The crossed designation is derived from the fact that two of the wires within the connection are crossed so that the send signal wire on one device becomes the receive signal of the other. Because the ports are crossed internally, a standard or straight-through cable can be used to connect devices.

Another type of port, called a Medium-Dependent Interface (MDI) port, is often included on a hub or switch to facilitate the connection of two switches or hubs. Because the hubs or switches are designed to see each other as an extension of the network, there is no need for the signal to be crossed. If a hub or switch does not have an MDI port, hubs or switches can be connected by using a cable between two MDI-X ports. The crossover cable uncrosses the internal crossing. Auto MDI-X ports on more modern network device interfaces can detect whether the connection would require a crossover, and automatically choose the MDI or MDI-X configuration to properly match the other end of the link.

A switch can work at either Layer 2 (the data link layer) or Layer 3 (the network layer) of the OSI model.

Hub

At the bottom of the networking food chain, so to speak, are hubs. Hubs are used in networks that use twisted-pair cabling to connect devices. Hubs also can be joined to create larger networks. Hubs are simple devices that direct data packets to all devices connected to the hub, regardless of whether the data package is destined for the device. This makes them inefficient devices and can create a performance bottleneck on busy networks.

In its most basic form, a hub does nothing except provide a pathway for the electrical signals to travel along. Such a device is called a passive hub. Far more common nowadays is an active hub, which, as well as providing a path for the data signals, regenerates the signal before it forwards it to all the connected devices. In addition, an active hub can buffer data before forwarding it. However, a hub does not perform any processing on the data it forwards, nor does it perform any error checking.

Hubs come in a variety of shapes and sizes. Small hubs with five or eight connection ports are commonly called workgroup hubs. Others can accommodate larger numbers of devices (normally up to 32). These are called high-density devices.

A basic hub works at Layer 1 (the physical layer) of the OSI model.

Bridge

A bridge, as the name implies, connects two networks. Bridging is done at the first two layers of the OSI model and differs from routing in its simplicity. With routing, a packet is sent to where it is intended to go, whereas with bridging, it is sent away from this network. In other words, if a packet does not belong on this network, it is sent across the bridge with the assumption that it belongs there rather than here.

If one or more segments of the bridged network are wireless, the device is known as a wireless bridge.

Modems

A modem (short for modulator/demodulator) is a device that converts the digital signals generated by a computer into analog signals that can travel over conventional phone lines. The modem at the receiving end converts the signal back into a format that the computer can understand. Modems can be used as a means to connect to an ISP or as a mechanism for dialing up a LAN.

Modems can be internal add-in expansion cards or integrated with the motherboard, external devices that connect to a system’s serial or USB port, or proprietary devices designed for use on other devices, such as portables and handhelds.

Wireless Access Point

The term access point can technically be used for either a wired or wireless connection, but in reality it is almost always associated only with a wireless-enabling device. Wireless access points (APs) are a transmitter and receiver (transceiver) device used to create a wireless LAN (WLAN). APs typically are a separate network device with a built-in antenna, transmitter, and adapter. APs use the wireless infrastructure network mode to provide a connection point between WLANs and a wired Ethernet LAN. APs also usually have several ports, giving you a way to expand the network to support additional clients.

Depending on the size of the network, one or more APs might be required. Additional APs are used to allow access to more wireless clients and to expand the range of the wireless network. Each AP is limited by a transmission range—the distance a client can be from an AP and still obtain a usable signal. The actual distance depends on the wireless standard used and the obstructions and environmental conditions between the client and the AP.

Saying that an AP is used to extend a wired LAN to wireless clients does not give you the complete picture. A wireless AP today can provide different services in addition to just an access point. Today, the APs might provide many ports that can be used to easily increase the network’s size. Systems can be added to and removed from the network with no effect on other systems on the network. Also, many APs provide firewall capabilities and Dynamic Host Configuration Protocol (DHCP) service. When they are hooked up, they give client systems a private IP address and then prevent Internet traffic from accessing those systems. So, in effect, the AP is a switch, DHCP server, router, and firewall.

APs come in all shapes and sizes. Many are cheaper and are designed strictly for home or small office use. Such APs have low-powered antennas and limited expansion ports. Higher-end APs used for commercial purposes have high-powered antennas, enabling them to extend how far the wireless signal can travel.

An AP works at Layer 2 (the data link layer) of the OSI model.

Media Converter

When you have two dissimilar types of network media, a media converter is used to allow them to connect. They are sometimes referred to as couplers. Depending on the conversion being done, the converter can be a small device, barely larger than the connectors themselves, or a large device within a sizable chassis.

Reasons for not using the same media throughout the network, and thus reasons for needing a converter, can range from cost (gradually moving from coax to fiber), disparate segments (connecting the office to the factory), or needing to run a particular media in a setting (the need for fiber to reduce EMI problems in a small part of the building).

Figure 4.3 shows an example of a media converter. The one shown converts between 10/100/1000TX and 1000LX (with an SC-type connector).

FIGURE 4.3 A common media converter

The following converters are commonly implemented and are ones that CompTIA has previously included on the Network+ exam.

Wireless Range Extender

A wireless range extender (also called a repeater or booster), can amplify a wireless signal to make it stronger. This increases the distance that the client system can be placed from the access point and still be on the network. The extender needs to be set to the same channel as the AP for the repeater to take the transmission and repeat it. This is an effective strategy to increase wireless transmission distances.

VoIP Endpoint

In the world of Voice over IP (VoIP), an endpoint is any final destination for a voice call. That final destination can be to a physical device (such as a physical telephone handset), a software application, or a server. Endpoints are used with the Session Initiation Protocol (SIP). To illustrate some of the possibilities, Cisco publishes an 18-page endpoint product matrix (available at https://www.cisco.com/c/dam/en/us/products/collateral/collaboration-endpoints/sales-tool-c96-739424.pdf.

Network Devices Summary

The information in this chapter is important for the Network+ exam. To summarize the coverage of network devices to this point, Table 4.1 lists some of the key points about each device. You should learn this information well.

TABLE 4.1 Network Devices Summary