5
Ethernet (802.3) Switched LANs
Last Name: _____________________________________
First Name: _____________________________________
Due Date: ___________________
Instructions
To receive credit, you must download these files and hand-write the answers. HWs must be turned into me prior to the associated chapter exam.
Ethernet Begins
1. What is a local area network (LAN)?
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2. a) At what layers are Ethernet standards defined?
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b) Are Ethernet messages packets or frames?
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c) Are Ethernet forwarding devices switches or routers?
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d) Is the path an Ethernet message takes a physical link, a data link, or a route?
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e) Does Ethernet use EUI-48 addresses or IP addresses?
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f) Why are Ethernet standards formally called 802.3 standards?
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3. a) _____ switches connect users to the network.
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b) _____ switches connect switches to other switches.
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c) _____ links connect users to workgroup switches.
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d) _____ links connect switches to other switches.
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Ethernet Physical Layer Standards
4. What four things do physical layer standards govern?
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5. a) Distinguish between binary and digital signaling.
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e) The 802.11ac Wi-Fi standard uses 256 states. How many bits can it send per clock cycle?
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f) Every time you double the number of states, how many more bits can you transmit? (The answer is not in the text.)
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g) Why is the signal held constant over each clock cycle?
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6. a) How many wires are there in Ethernet cable?
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f) What propagation problem limits transmission distance in 4-pair UTP?
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7. a) If you need to transmit 600 million bits per second 90 meters, what signaling standard and UTP quality standard would you use?
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b) If you need to transmit 7 Gbps 40 meters, what signaling standard and UTP quality standards could you use?
Ethernet Signaling Standard
Transmission Speed
Cable Quality Category
Maximum Cord Length
100BASE-TX
100 Mbps
Cat 5e, 6, 6A
100 meters
1000BASE-T
1 Gbps
Cat 5e, 6, 6A
100 meters
2.5GBASE-Ta
2.5 Gbps
Cat 5e, 6, 6A
100 meters
5GBASE-Ta
5 Gbps
Cat 5e, 6, 6A
100 meters
10GBASE-T
10 Gbps
Cat 6, Cat 6A
55 meters
10GBASE-T
10 Gbps
Cat 6A
100 meters
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c) Which would you probably use if you wanted to send the signal over installed cabling?
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8. For what specific purpose were the 2.5GBASE-T and 5GBASE-T standards developed?
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9. a) How does fiber usually transmit a 1?
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b) How do fiber cords typically provide full-duplex transmission?
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c) In what units are light wavelengths measured?
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d) What are the three wavelength windows used in fiber transmission?
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e) What is amplitude?
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10. a) What is a mode?
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b) What is multimode fiber?
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c) What limits transmission distance in multimode fiber?
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g) What is the quality designator for multimode optical fiber?
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In More Depth: Fiber Modes and Light Wavelength
14. a) Compare relative cost and maximum propagation distance for multimode and single-mode fiber.
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b) Why does multimode fiber dominate LAN installations?
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c) For LAN fiber, what is the dominant signal wavelength?
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d) Why does this wavelength dominate?
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The Ethernet Data Link Layer Switching and Frame Syntax Standard
16. a) Do switches know the entire data link between the source and destination host?
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b) What does a switch know?
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17. a) How are switches in an Ethernet LAN organized?
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b) Because of this organization, how many possible paths can there be between any two hosts?
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c) In Figure 5-2 what is the single possible path between Client PC 1 and Server X? Just give the letters of the switches.
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18. a) What is the benefit of having a single possible path through an Ethernet network?
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b) Why has Ethernet become the dominant LAN technology?
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19. a) Are Ethernet EUI-48 addresses expressed in hex for humans, devices, or both?
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b) Which letters may appear in a hex EUI-48 address?
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c) What is 5 hex in binary?
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l) Convert A1-B2-C3-44-5D-3C to binary. Leave a space between each octet. As a check, there must be 48 bits.
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In More Depth: Secondary Fields in the Ethernet Frame
20. a) What information do the two tag fields give?
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b) When is the PAD Field added?
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Management
21. a) What protocol do companies use to manage their Ethernet networks?
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b) What are manageable switches?
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c) Are all Ethernet switches manageable?
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22. a) What reliability problem does Ethernet have?
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b) How can some redundant backup links be installed without creating loops?
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c) Is this easy to do?
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Ethernet Security
23. a) What is the security benefit of Ethernet VLANs?
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b) In Figure 5-28, to which hosts can Host D4… send frames?
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24. a) What security threat is 802.1X designed to protect against?
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b) When 802.1X is being used, what happens if an attacker plugs his or her host into a switch?
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25. What type of attack does 802.1AE protect against?
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26. a) Before the attack, where does the ARP cache tell the victim to send a frame carrying a packet to the router?
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b) Where does it tell the victim to send such frames after the attack?
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c) What harm can the attacker do?
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End-of-Chapter Questions
5-1. a) If both UTP and optical fiber can be used for a particular physical link, which should I choose? Why?
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c) Some companies are now installing OM4 even when OM3 can do the job. Why do you think they do that?
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5-2. What Work Group of the 802 LAN/MAN Standards Committee developed the 802.1X and 802.1AE standards? This working group, by the way, creates security and management standards for use in all other Working Groups.
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5-3. In ARP cache poisoning, the attacker poisons the victim’s ARP cache. This allows the attacker to read frames that the victim sends to the router. How can it read the frames that the victim receives from the router?
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5-4. Can you think of a way to allow a client on one virtual LAN to communicate with a server on another VLAN. Hint: Switches typically have no way of doing it. Hint 2: It involves an access control list or some other type of device. The ACL permits specific client-server host pairs to communicate.
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