Ch 6: Basic Catalyst Switch Operations

Which of the following is an advantage of switches over hubs? ❍ A. Switches provide full-duplex microsegmentation of collision domains. ❍ B. Switches' low cost compared to hubs makes them an attractive choice for growing businesses. ❍ C. Although they cannot segment broadcast domains, switches' much greater speed still makes them a desirable upgrade. ❍ D. Switches are impervious to security threats by definition and provide a secure Layer 2 solution out of the box.

Answer A is correct. Switches, when they are configured correctly, can eliminate collisions from the LAN. This design of creating a single collision domain for each connected device is called microsegmentation. Answer B is incorrect; switches cost more than hubs. Answer C is incorrect; switches can segment broadcast domains through the use of VLANs. Answer D is incorrect; switches are not inherently secure and should have basic security measures applied.

Which of the following explains why full-duplex operation is desirable? ❍ A. Full duplex allows for the detection of collisions so that data can be retransmitted when the wire is free. ❍ B. Full duplex allows simultaneous transmit and receive functions, providing higher overall throughput. ❍ C. Full duplex provides inter-VLAN routing capability. ❍ D. Full duplex can take advantage of existing coaxial cabling.

Answer B is correct. Full duplex uses two pairs to establish separate send and receive circuits, effectively doubling potential throughput. Answer A is incorrect; full duplex disables the collision-detection circuit because it is no longer required. Answer C is incorrect; inter-VLAN routing capability is a Layer 3 function available only on certain switches and has nothing to do with duplex setting (Layer 1). Answer D is incorrect; full duplex cannot work on coaxial cabling because there is only one pair of conductors, and full duplex requires two.

What is the function of 802.1d STP? ❍ A. Prevents routing loops in redundant topologies ❍ B. Prevents Layer 2 loops in networks with redundant switched paths ❍ C. Prevents frame forwarding until all IP addresses are known ❍ D. Enables the use of multiple routed paths for load-sharing ❍ E. Allows the propagation of VLAN information from a central source

Answer B is correct. STP prevents Layer 2 loops if redundant paths exist. Answers A, C, D, and E are incorrect; STP is not concerned with routing loops, IP addresses, routing in general, or VLAN administration.

Which switching mode sacrifices speed for error-free switching? ❍ A. Segment-Free ❍ B. Store and Forward ❍ C. Cut Throat ❍ D. Fragment Free ❍ E. Cut Through

Answer B is correct. Store and Forward is the slowest mode but has the advantage of fully error checking every frame for reliability. Answers A, C, D, and E are incorrect. There is no such thing as Segment-Free or Cut-Throat switching. Fragment Free examines the first 64B of every frame for increased reliability, but is not as fast as Cut-Through.

You currently have seven hubs that form the LAN in your office, to connect 12 servers and 30 users. You have the budget to buy one 24-port switch. What is the most efficient way to utilize your limited switch resources? ❍ A. Connect all the hubs to each other, and then connect the string of hubs to one switch port. ❍ B. Connect each hub to a single switch port. ❍ C. Connect each hub to a single switch port. Move the servers to their own switch ports. Move active user PCs to the remaining switch ports, leaving the less-active PCs attached to hubs. Distribute the remaining PCs evenly across the hubs. ❍ D. Connect each hub to the switch with 2 or 3 cables to provide additional bandwidth.

Answer C is correct. Doing this will ensure that the most important devices have the best possible data access speed. Answer A is incorrect; this creates a single large collision domain with minimal bandwidth. Answer B is not wrong, it is just not the best answer; in doing this you create several collision domains, but do not make the best use of the switch resources. Answer D is incorrect; this could create nasty loops in your network, and to take advantage of the potential bandwidth both devices would need to be compatible switches—hubs can't do the intended function.

How many collision and broadcast domains exist on a 12-port switch with default configuration? ❍ A. 2 collision domains, 12 broadcast domains ❍ B. 1 collision domain, 12 broadcast domains ❍ C. 1 collision domain, 1 broadcast domain ❍ D. 12 collision domains, 1 broadcast domain

Answer D is correct. Each port on a switch is a collision domain. Answers A, B, and C are incorrect; with a default configuration (that is, a single VLAN), a switch creates one broadcast domain.

What is the most common Layer 2 device? ❍ A. Hub ❍ B. Repeater ❍ C. Router ❍ D. Switch ❍ E. Bridge

Answer D is correct. Switches are by far the most common Layer 2 device in use. A, B, and C are incorrect because hubs, repeaters, and routers are not Layer 2 devices. (Hubs and repeaters are Layer 1; routers are Layer 3.) Answer E is incorrect because switches are much more common than bridges.

What happens when a switch receives a frame with the destination MAC address of FF-FF-FF-FF-FF-FF? ❍ A. The switch drops the frame and sends a "Destination Unreachable" message back to the source. ❍ B. The switch forwards the frame out the port that connects to the host with that MAC address. ❍ C. The switch filters the frame because the address is not valid. ❍ D. The switch floods the frame out all ports except the one it came in on.

Answer D is correct. The MAC address shown is the broadcast address, so the switch will perform the flood operation. Answer A is what a router would do to a packet it has no route for. Answer B is what the switch would do with a frame whose address is in the MAC address table, and Answer C, the filter operation, happens only when the source and destination addresses are on the same port.

What devices and functions can an administrator use to segment the network, assuming that no VLANs are used? Choose all that apply. ❍ A. Routers to segment broadcast domains ❍ B. Switches to segment broadcast domains ❍ C. Switches to increase the number of collision domains ❍ D. Bridges to segment collision domains ❍ E. Hubs to segment collision domains ❍ F. Bridges to segment broadcast domains ❍ G. Repeaters to segment broadcast domains

Answers A, C, and D are correct. Routers segment broadcast domains; switches and bridges segment (increase the number of) collision domains. Answers B, E, F, and G are incorrect. The question stipulates that VLANs are not in use, so a switch does not segment broadcast domains. Hubs and repeaters extend and enlarge, not segment, collision and broadcast domains. Bridges do not segment broadcast domains.

Which of the following are true of switches and bridges? Choose all that apply. ❍ A. Switches have fewer ports and switch in software. ❍ B. Switches have a higher port density and switch using ASIC hardware. ❍ C. Bridges are faster than switches. ❍ D. Switches are faster than bridges. ❍ E. Switches create only one broadcast domain by default. ❍ F. Bridges create only one broadcast domain.

Answers B, D, E, and F are correct. Switches have more ports than bridges and are faster than bridges. Watch out for the trick: Both switches and bridges create only one broadcast domain. Answers A and C are incorrect.