Answers and Explanations
A1: Answer: C. Switches provide a separate circuit for each interface, and thus provide a separate collision domain for each interface. A is incorrect because hubs do not process frames. B is incorrect because hubs suffer from collisions that decrease bandwidth. D is incorrect, as switches flood received broadcasts.

A2: Answers: A and D. Half-duplex Ethernet typically operates in a shared collision domain. This allows only one device to send or receive data at a time. If any additional devices attempt to transmit, a collision results. Network hubs operate in this manner. Because of this limitation, half-duplex has lower effective throughput than full-duplex, so D is correct as well. B is incorrect, as full-duplex connections typically operate in a private collision domain. C is incorrect because full-duplex has a higher effective throughput. E is incorrect, as Ethernet has no control over broadcasts.

A3: Answer: D. You must be in VLAN Configuration mode for VLAN1. A is incorrect because you cannot configure IP addresses in Privileged EXEC mode. B is incorrect because that is not a valid command. C is incorrect because you must specify the subnet mask when performing this command.

A4: Answer: A. Store-and-forward transmission checks the entire length of the frame before sending it out the appropriate interface or interfaces. B is incorrect, as there is no such method. C is incorrect, as cut-through transmission sends the frame through as soon as the destination MAC address is read. D is incorrect, as fragment-free transmission checks the first 64 bytes before sending the frame.

A5: Answers: A, D, and E. By default, a switch boots up with the following configuration:

No IP address

CDP Enabled

Ports Auto-Negotiate

Spanning-Tree Enabled

No Console Password

A6: Answers: B and D. MAC addresses are 48-bit hexadecimal numbers that are often shown as 12 digits. The allowable values in hexadecimal are 0–9 and A–F. Answer A has too many digits, and C and E include the letter G.

A7: Answers: B and C. Bridges build the bridge table by listening to incoming frames and examining the source MAC address in the frame. Switches are multiport bridges that allow you to create multiple collision domains. A is incorrect, as bridges are software-based, and switches have hardware that assist in speeding up transactions. D is incorrect, as both bridges and switches forward broadcasts.

A8: Answer: C. Cisco and other networking companies refer to the addition of segments on a network as microsegmentation. Answers A, B, and D are not real terms.

A9: Answer: D. As the frame check sequence (FCS) is located in the frame trailer, only store-and-forward switching, which buffers the whole frame before sending it, is able to perform such checks. A is incorrect, as store-and-forward is the slowest of all transmission types. B is incorrect, as the switch uses more memory to store the incoming frames. C is incorrect, as store-and-forward and cut-through are nonproprietary.

A10: Answer: A. By issuing the ip-default gateway command, you are specifying a router that the switch can send frames to if they are sent outside the network segment. This is necessary whenever you want to telnet to a switch from a remote network. B is a nonexistent command on a switch. C is used only on routers. D is a nonexistent command.

A11: Answer: D. Spanning-Tree Protocol was developed by DEC and updated by the IEEE 802.1d standard. It dynamically monitors your switched environment and blocks ports to stop loops from happening in your switched environment. A and C are incorrect, as they do not contain or create routing loops. B is incorrect because STP does not stop broadcasts.

A12: Answer: C. When a port is in Learning mode, it learns MAC addresses and places them into the Content Addressable Memory (CAM) table, but it does not forward data frames. This allows the switch to know the MAC address(es) connected to the port before the port begins forwarding. A and B are incorrect, as both of those modes do not learn MAC addresses. D is incorrect because the port learns MAC addresses as well as forwards frames.

A13: Answer: D. Designated ports on a network segment are placed into a forwarding state. A is incorrect, as nondesignated ports are placed into a blocked state. While designated ports transition through the listening and learning states, they do not remain there; thus, B and C are incorrect.

A14: Answer: C. The convergence time of 802.1d STP is approximately 50 seconds. Thus A, B, and D are incorrect.

A15: Answer: C. The 24 FastEthernet Ports operate at 100Mbps in either full- or half-duplex mode. In half-duplex mode, they have 100Mbps to send or receive traffic. If changed to full-duplex mode, the hosts have 100Mbps to send and 100Mbps to receive (theoretically doubling the amount of bandwidth). Answers A, B, and D are incorrect values.

A16: Answer: A. If you issue the command no cdp run, the switch does not allow CDP frames to be sent out of any interface on the switch. This command is given in Global Configuration mode. B is incorrect, as it disables CDP only on a particular interface. C and D are not valid commands, and thus are incorrect.

A17: Answer: B. If you issue the command no cdp enable, the switch disables CDP advertisements on a particular interface. A is incorrect, as no cdp run disables all interfaces. C and D are not valid commands, and thus are incorrect.

A18: Answer: C. Bridge Protocol Data Units are used by STP to monitor the switched environment and perform root bridge elections. A is incorrect, as packets are Layer 3 data units, whereas Spanning-Tree is Layer 2. B is incorrect, as data frames are not affected by STP. D is incorrect because VTP is used to advertise VLAN information to other switches.

A19: Answer: B. Bridge ID is made up of the bridge priority and MAC address of a particular port. The lowest bridge ID for a switch on a network segment becomes the root bridge. A and C are incorrect, as a BPDU does not have these items. D is incorrect, as the MAC address by itself is not enough to choose the root bridge; rather, it is combined with the bridge priority field to create the bridge ID.

A20: Answers: A and B. Full-duplex requires point-to-point links and provides collision-free operation, as it has a separate pair of wires for transmitting and receiving. C is incorrect, as it has no need to reschedule transmissions. D is incorrect, as two pairs of wires for transmitting and receiving are necessary for full-duplex.

A21: Answer: D. You make the speed and duplex settings in Interface Configuration mode. A, B, and C are incorrect, as those modes do not allow you to make speed and duplex changes.

A22: Answer: C. When you decrease the default bridge priority of 32768, you ensure that the switch will have the lowest bridge ID. A is incorrect, as the MAC address is a burned-in address on the interfaces. B is incorrect, as the lowest bridge ID decides the root bridge, not the highest. D is incorrect, as the router ID is used in OSPF, which is not a Layer 2 switch ability.

A23: Answers: D and E. Modified cut-through transmission (also known as fragment-free) checks the first 64 bytes of a frame before forwarding it out. A is incorrect, as store-and-forward transmission waits until the entire frame is checked before sending it out. B is incorrect, as cut-through transmission checks the destination address only before forwarding. C is not a valid frame transmission method.

A24: Answer: A. When you are configuring port security, all commands begin with the switchport port-security syntax. In addition, the port must be configured as an access port before the port-security features will function (by typing switchport mode access). The switchport port-security command enables the port-security feature. You must then add your MAC addresses using the switchport port-security mac-address command. Finally, using the switchport port-security violation shutdown command instructs the port to shut down when it sees a bad MAC address. All other answers are missing one or more critical pieces of this syntax.

A25: Answer: D. The show port-security interface fa0/20 command allows you to see any port security features you have enabled on an interface. A is incorrect because the show interface command just shows you port statistics such as the number of packets and bytes sent and received. B is incorrect because this command shows you Layer 3 statistics for the interface, and is typically used for routed interfaces. Answer C is incorrect because this command displays the access or trunking characteristics of the port.

A26: Answer: C. The 802.3 protocol specifies Ethernet. A is incorrect; 802.1 standards specify general networking recommendations and requirements, which are media- and vendor-neutral. The 802.1 protocol also specifies bridging/switching standards. B is incorrect, as 802.2 protocols specify the Logical Link Control sublayer of the Data Link layer. D is incorrect, as 802.5 specifies token ring technologies.

A27: Answer: A. Full-duplex requires a point-to-point connection, and a switch connecting to another switch provides it. B, C, and D are incorrect because any device connecting to a hub is not considered a point-to-point connection.

A28: Answer: E. You make this configuration setting on a particular interface, thus the need to be in Interface Configuration mode. A and C are incorrect because the commands are given in the wrong configuration mode. B, D, and F are incorrect commands.

A29: Answers: C and E. Hubs work on half-duplex mode. If more devices connect to a hub and are sending simultaneously, collisions occur. ARP and IPX SAP traffic is broadcast-based and also creates congestion in the network. A is incorrect, as the creation of a new collision domain means connecting a switch instead of a hub. This does not contribute to congestion. B is incorrect, as the creation of VLANs in a switch isolates a broadcast domain. D is incorrect, as switches help contain congestion.

A30: Answers: A and D. For an administrator to remotely manage a switch, an IP address must be assigned, and a default gateway must be set for return traffic. B is incorrect, as a routing protocol is not mandatory; static routes can be used. C is incorrect, as some routers and switches can use half-duplex to communicate. E is incorrect, as you do not need a route from the router to the switch; that's what the default gateway accomplishes.

A31: Answer: D. Spanning-Tree Protocol (STP) ensures that there are no loops in your redundant switched network. When a port or switch fails, STP converges through four stages, taking approximately 50 seconds to do so. A, B, and C are incorrect times of convergence, even when using STP modifications such as PortFast, BackboneFast, and UplinkFast.

A32: Answer: C. When STP is merely monitoring the switched network and all ports are in their appropriate blocking or forwarding state, it is known as a converged network. A is incorrect; although you might describe a converged network as stable, it is not the correct definition. B is incorrect, as blocking is a port state. D is incorrect, as STP dynamically monitors the switched network for any changes because of failed switches or disabled ports.

A33: Answer: B. The Protocol Data Units (PDUs) that operate at Layer 2 of the OSI Model are called frames. A is incorrect, as bits are at Layer 1. C is incorrect, as packets are at Layer 3. D is incorrect, as segments are at Layer 4.

A34: Answers: A and D. Full-duplex provides separate transmit and receive circuits, thus effectively doubling the total bandwidth. Because of this behavior, it requires point-to-point connections. B is incorrect, as full-and half-duplex are Ethernet behaviors, not token ring, which relies on token passing. C is incorrect, as full-duplex, with its separate transmit and receive circuits, does not have collisions.

A35: Answer: C. By default, Layer 2 switches cannot stop broadcasts, and floods them out all ports except the port on which the broadcast was received. A is incorrect as it reads, because adding more ports means adding more end-user broadcasts. B is incorrect, as switches are not efficient with forwarding broadcasts: They flood broadcasts out all ports by default. Only by using VLANs are they able to control broadcasts. D is incorrect, as switches do not "process" broadcasts; they merely flood them out all other ports. However, CPU utilization increases on PCs.

A36: Answer: D. Adjusting your spanning-tree priority to a lower number reduces the switch Bridge ID. This makes it more likely to become the root of the spanning-tree network. The lower the switch Bridge ID, the more likely the chance of becoming the root. Answer A is incorrect because there is no spanning-tree root command. You could use the spanning-tree vlan 1 root primary command, which automatically lowers the Bridge Priority to 4096. Answer B is incorrect, as you are not able to change the MAC address your switch uses for STP in this way. Answer C is incorrect because you need to dictate which VLAN the STP priority is changed for (because Cisco switches run an instance of STP per VLAN). In addition, adjusting the priority to a higher number makes it less likely to become the root.

A37: Answer: E. You make this configuration setting on a particular interface, thus the need to be in Interface Configuration mode. A and C are incorrect, as the commands are given in the wrong configuration mode. B, D, and F are incorrect commands.

A38: Answers: A, B, and C. The correct command is duplex [full/half/auto]. D is incorrect, as control is not a duplex setting on a Catalyst switch.

A39: Answers: B and D. MAC addresses are 48-bit hexadecimal numbers that are often shown as 12 digits. The allowable values in hexadecimal are 0–9 and A–F. A is incorrect because it has too many digits. C and E are incorrect because they include the letter X.

A40: Answer: A. A media access control (MAC) address is a unique physical address that is "burned" into a network interface. It operates at Layer 2 of the OSI Model. B is incorrect because there is no such thing. C is incorrect, as an IP address is a logical address that can be assigned or changed, and it operates at Layer 3 of the OSI Model. D is incorrect, as IPX is a Novell proprietary protocol that operates at Layer 3 of the OSI Model.

A41: Answer: C. A switch helps provide more collision domains, thus keeping collisions from occurring. A and B are incorrect, as hubs and repeaters cannot segment your network; they merely retransmit whatever comes in. D is incorrect, as a terminal adapter is used to connect a non–ISDN-ready device to a NT1.

A42: Answer: C. Virtual local area networks (VLANs) allow a switch to separate ports into different network segments or broadcast domains. A is incorrect, as CDP is used by Cisco devices to share management information. B is incorrect because RIP is a routing protocol that is not used by Layer 2 switches. D and E are incorrect, as duplex settings do not help set up broadcast domains.

A43: Answer: C. The show mac-address-table command reports all static and dynamically learned MAC addresses to the terminal. A is incorrect, as the show ip interface command is used to verify routed interfaces on a router or L3 switch. B and D are incorrect, as there are no such commands.

A44: Answer: D. Hubs are notorious for allowing collisions in a network, as they operate on a shared-wire technology. A is incorrect, as full-duplex does not allow collisions. B is incorrect, as creating collision domains lessens collisions and congestion. C is incorrect, as creating a broadcast domain decreases the number of broadcasts (which cause congestion) in your network.

A45: Answer: A. Store-and-forward transmission buffers the entire contents of the frame before sending it out. B is incorrect, as cut-through transmission sends the frame through as soon as the destination MAC address is read. C and D are incorrect, as modified cut-through and fragment-free transmission check the first 64 bytes before sending the frame.

A46: Answer: D. The hexadecimal value of 215 is 0xAA, which equals 11010111 in binary. A, B, and C equal 186, 159, 170, respectively.

A47: Answer: A. The hexadecimal value of 105 is 0x69, which equals 1101001 in binary. B, C, and D equal 35, 170, and 215, respectively.

A48: Answer: A. The binary 10110010 is the equivalent of the hexadecimal 0xB2. B, C, and D equal 0xB5, 0xCC, and 0xD4, respectively.

A49: Answer: C. Hubs do not separate each port into a separate collision domain. Separate collision domains grant dedicated bandwidth to each port, and thus each end user plugged into that port. A is not correct, as hubs can extend the length of an Ethernet segment. Hubs are also known as multiport repeaters. B is incorrect, as hubs do offer half-duplex connections. D is incorrect, as there are hubs that support FastEthernet connections.

A50: Answer: D. The 802.1d STP can listen to up to seven consecutive hops, or switches chained together, before it is unable to monitor the topology. This is sometimes known as the STP radius. A, B, and C are incorrect, as STP can handle up to seven hops, and the question asks for the maximum. E is incorrect, as it exceeds the maximum of seven.