Questions and Answers
What is the primary function of a repeater in a LAN?
To regenerate and retime the original bit pattern of incoming signals
What happens to a packet arriving at a hub from station A to station B?
It is broadcast to all stations except the one that sent it
At which layers of the OSI model does a link-layer switch operate?
Physical and data-link layers
What does a link-layer switch do when it receives a frame with a destination MAC address not in its table?
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What is the purpose of a link-layer switch's table?
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What happens when a learning switch does not have an entry for a destination MAC address in its table?
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What is the primary goal of the Spanning Tree Algorithm in Step 2?
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What is the purpose of the forwarding ports in the Spanning Tree Algorithm?
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What is the purpose of the blocking ports in the Spanning Tree Algorithm?
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What is the primary function of a router?
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What is the technology used to connect the two LANs in the example given in Figure 17.9?
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What is the result of applying the Spanning Tree Algorithm to a network?
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When a station moves from one VLAN to another, what happens to the broadcast messages it receives?
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What is the primary purpose of grouping stations in a VLAN?
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What is the method by which stations are configured to belong to a VLAN?
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In a multi-switched backbone, how do switches communicate with each other to determine VLAN membership?
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What is one of the advantages of using VLANs in a network?
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What is the characteristic used to group stations in a VLAN, according to vendors?
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What is the primary function of the Dynamic Host Configuration Protocol (DHCP) in an organization?
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What is the main benefit of using Network Address Translation (NAT) in a small network?
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What happens when a router receives a packet while processing another packet?
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What is the consequence of packet loss on the Internet network layer?
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How many bits are used for the Host ID in a 220.8.24.128/25 network?
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What is the primary goal of congestion control?
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What is the maximum number of sub-networks possible in a 220.8.24.128/25 network?
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What are the two metrics used to measure the performance of a network in congestion control?
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What is the purpose of DHCP in relation to TCP/IP?
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What is the primary reason for using NAT in most situations?
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What are the two approaches to congestion control?
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What is the relationship between congestion at the network layer and congestion at the transport layer?
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Study Notes
Repeaters and Hubs
- A repeater is a multiport device that receives a signal, regenerates and retimes the original bit pattern, and forwards the packet from all outgoing ports except the one from which the signal was received.
- This process is called broadcasting, and all stations in the LAN receive the frame, but only the intended recipient keeps it.
Link-Layer Switches
- A link-layer switch operates in both the physical and data-link layers, regenerating the signal it receives and checking the MAC addresses contained in the frame.
- The switch forwards the frame only through the port that corresponds to the destination MAC address.
- If the switch does not have an entry for the destination MAC address, it will broadcast the frame to all ports.
VLANs
- VLAN (Virtual Local Area Network) technology allows the grouping of stations connected to different switches in a VLAN.
- Stations can be grouped based on characteristics such as interface numbers, port numbers, MAC addresses, IP addresses, IP multicast addresses, or a combination of two or more of these.
- Stations are configured into VLANs manually, automatically, or semi-automatically.
- In a multi-switched backbone, each switch must know the membership status of stations connected to other switches, which can be achieved through table maintenance, frame tagging, or time-division multiplexing.
- Advantages of VLANs include reducing packet loss, improving performance, and increasing security.
Congestion Control
- Congestion control refers to the mechanisms and techniques used to control congestion and keep the load below the capacity of the network.
- Congestion control involves two metrics: delay and throughput.
- Congestion control techniques can either prevent congestion before it happens or remove congestion after it has happened.
Network Address Translation (NAT)
- NAT enables a user to have a large set of addresses internally and a small set of addresses externally.
- NAT provides the mapping between private and universal addresses, supporting virtual private networks.
Spanning Tree Algorithm
- The Spanning Tree Algorithm is used to prevent loops in a network.
- Step 1: Select a root switch.
- Step 2: Find the shortest path from the root switch to every other switch or LAN.
- Step 3: Mark the ports that are part of the spanning tree (forwarding ports) and those that are not part of the spanning tree (blocking ports).
Routers
- A router is a three-layer device that operates in the physical, data-link, and network layers.
- Routers can be used to connect multiple LANs to form a larger LAN.
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