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This chapter is from the book

Review and test yourself

The following sections provide you with the opportunity to review what you learned in this chapter and to test yourself.

The facts

  • Both hubs and switches are used in Ethernet networks. Token Ring networks, which are few and far between, use special devices called multistation access units (MSAUs) to create the network.

  • The function of a hub is to take data from one of the connected devices and forward it to all the other ports on the hub.

  • Most hubs are considered active because they regenerate a signal before forwarding it to all the ports on the device. In order to do this, the hub needs a power supply.

  • Rather than forwarding data to all the connected ports, a switch forwards data only to the port on which the destination system is connected.

  • Switches make forwarding decisions based on the Media Access Control (MAC) addresses of the devices connected to them to determine the correct port.

  • In cut-through switching, the switch begins to forward the packet as soon as it is received.

  • In a store-and-forward configuration, the switch waits to receive the entire packet before beginning to forward it.

  • FragmentFree switching works by reading only the part of the packet that enables it to identify fragments of a transmission.

  • Hubs and switches have two types of ports: Medium Dependent Interface (MDI) and Medium Dependent Interface-Crossed (MDI-X).

  • A straight-through cable is used to connect systems to the switch or hub using the MDI-X ports.

  • In a crossover cable, wires 1 and 3 and wires 2 and 6 are crossed.

  • Both hubs and switches come in managed and unmanaged versions. A managed device has an interface through which it can be configured to perform certain special functions.

  • Bridges are used to divide up networks and thus reduce the amount of traffic on each network.

  • Unlike bridges and switches, which use the hardware-configured MAC address to determine the destination of the data, routers use the software-configured network address to make decisions.

  • With distance-vector routing protocols, each router communicates all the routes it knows about to all other routers to which it is directly attached.

  • RIP is a distance routing protocol for both TCP and IPX.

  • Link state protocols communicate with all other devices on the network to build complete maps of the network. They generate less network traffic than distance vector routing protocols but require more powerful network hardware.

  • Open Shortest Path First (OSPF) and NetWare Link State Protocol (NLSP) are the most commonly used link state routing protocols used on IP and IPX networks respectively.

  • The term gateway is applied to any device, system, or software application that can perform the function of translating data from one format to another.

  • A CSU/DSU acts as a translator between the LAN data format and the WAN data format.

  • Wireless network devices gain access to the network via Wireless Access Points.

  • Modems translate digital signals from a computer into analog signals that can travel across conventional phone lines.

Key terms

  • Hub

  • Bridge

  • Gateway

  • Network Interface Cards

  • ISDN adapters

  • Switch

  • Router

  • CSU/DSU

  • System area network cards

  • Wireless Access Points (WAPs)

  • Modems

  • MAC addresses

  • Distance vector

  • Link state

  • Dynamic routing

  • Static routing

  • NLSP

  • OSPF

  • RIP

  • Convergence

  • Bridging loops

Practice exam

Question 1

Users are complaining that the performance of the network is not satisfactory. It takes a long time to pull files from the server and, under heavy loads, workstations can become disconnected from the server. The network is heavily used and a new video conferencing application is about to be installed. The network is a 100BaseT system created with Ethernet hubs. Which of the following devices are you most likely to install to alleviate the performance problems?

  1. Switch

  2. Router

  3. Bridge

  4. Gateway

The correct answer is A. Replacing Ethernet hubs with switches can yield significant performance improvements. Of the devices listed, they are also the only one that can be substituted for hubs. Answer B, router, is incorrect as a router is used to separate networks, not as a connectivity point for workstations. A bridge could be used to segregate the network and so improve performance, but a switch is a more obvious choice in this example. Therefore, answer C is incorrect. Answer D, gateway, is incorrect. A gateway is a device, system, or application that translates data from one format to another.

Question 2

Which of the following devices forwards data packets to all connected ports?

  1. Router

  2. Switch

  3. Bridge

  4. Hub

The correct answer is D. Hubs are inefficient devices that send data packets to all connected devices. Many of today's networks are upgrading to switches that pass data packets to the specific destination device. This method significantly increases network performance.

Question 3

Of the following routing methods, which is likely to take the most amount of administration time in the long term?

  1. Static

  2. Link state

  3. Distance vector

  4. Dynamic

The correct answer is A. Static routing will take more time to administer in the long term, as any changes to the network routing table must be entered manually. Answers B and C are incorrect. Distance vector and link state are both dynamic routing methods. Answer D is also incorrect. Dynamic routing might take more time to configure initially, but in the long term it will require less administration time. It can adapt to changes in the network layout automatically.

Question 4

Your manager asks you to look into some upgrades for your network. The current network is a 10Base2 system and you have been experiencing numerous hard-to-track-down cable problems. As a result, you have decided to upgrade to a 10BaseT system. On the networking vendor's price list are both active and passive hubs. The passive hubs are considerably cheaper than the active ones and you are tempted to opt for them so that you come in under budget. A colleague advises you against the purchase of passive hubs. What is the primary difference between an active and a passive hub?

  1. Passive hubs do not offer any management capabilities.

  2. Passive hubs cannot be used in full-duplex mode.

  3. Passive hubs do not regenerate the data signal.

  4. Passive hubs forward data to all ports on the hub, not just the one for which they are intended.

The correct answer is C. An active hub regenerates the data signal before forwarding it. Answer A is incorrect. The management capabilities of a hub have nothing to do with the active/passive aspect of the device. Answer B is incorrect. Hubs are not able to operate in full-duplex mode. Only network switches are able to perform this function in this context. Answer D describes the function of a switch, not a hub.

Question 5

Which of the following statements best describes a gateway?

  1. It is a device that allows data to be routed from one network to another.

  2. It is a term used to refer to any device that resides at the entrance of a network.

  3. It is a device, system, or application that translates data from one format to another.

  4. It is a network device that can forward or block data based on the MAC address embedded within the packet.

The correct answer is C. A gateway can be a device, system, or application that translates data from one format to another. Answers B and D are more likely to describe a router than a gateway. Answer D describes a bridge. A bridge is a device that is used to segregate a network. It makes forwarding or blocking decisions based on the MAC address embedded within the packet.

Question 6

You have a thin coaxial-based Ethernet network and are experiencing performance problems on the network. By using a network performance-monitoring tool, you determine that there are a large number of collisions on the network. In an effort to reduce the collisions you decide to install a network bridge. What kind of bridge are you most likely to implement?

  1. Collision bridge

  2. Transparent bridge

  3. Visible bridge

  4. Translational bridge

The correct answer is B. A transparent bridge can be used to segment a network, which reduces the amount of collisions and the overall network traffic. It is called transparent because the other devices on the network do not need to be aware of the device and will in fact operate as if it wasn't there. Answer D is incorrect as a translational bridge is used in environments where it is necessary to translate from one data format to another. Such a conversion is not necessary in this scenario. Answers A and C are invalid. There is no such thing as a collision bridge or a visible bridge.

Question 7

Which of the following represents a valid MAC address?

  1. 00-D0-56-F2-B5-12

  2. 00-63-T6-4H-7U-78

  3. 00-62-DE-6F-D2

  4. 000-622-DE5-75E-EA6

The correct answer is A. A MAC address is a 6-byte address which is expressed in hexadecimal format. Answer B contains the letters T and U, which are not valid. Hexadecimal format uses only numbers and the letters A through F. For this reason, answer B is incorrect. Answer C is only five bytes and so is incorrect. Answer D is incorrect because a byte in hexadecimal is expressed in two characters and the answer uses three.

Question 8

Which of the following devices passes data based on the MAC address?

  1. Hub

  2. Switch

  3. MSAU

  4. Router

The correct answer is B. When determining the destination for a data packet, the switch learns the MAC address of all devices attached to it and then matches the destination MAC address in the data it receives. None of the other devices pass data based solely on the MAC address.

Question 9

What is the speed of the 16550 UART chip?

  1. 921,600

  2. 430,800

  3. 115,200

  4. 9600

The correct answer is C. 115,200 is the speed of the 16550 UART chip. Answer A is incorrect as 921,600 is the speed of the 16750 and 16950 UART chips. Answer B is incorrect as 430,800 is the speed of the 16650 UART chip and 9600 is the speed of the 8250 UART chip.

Question 10

Which of the following devices would you find only on a Token Ring network?

  1. Hub

  2. Switch

  3. MSAU

  4. Router

The correct answer is C. A Multistation Access Unit (MSAU) is used as the connectivity point on a Token Ring network. Answers A and B are incorrect. Switches and hubs are associated with Ethernet networks. Answer D is incorrect. Routers can be found on both Token Ring and Ethernet networks.

 

Want to know more?

Sheldon, Thomas. McGraw-Hill's Encyclopedia of Networking and Telecommunications. McGraw-Hill Professional Publishing, 2001.

Tulloch, Mitch. Microsoft Encyclopedia of Networking (with CD-ROM). Microsoft Press, 2000.

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