A P P E N D I X A

Answers to the “Do I Know This Already?” Quizzes and Q&A Questions

Chapter 1

“Do I Know This Already?” Quiz

1.Which of the following statements describes part of the process of how a switch decides to forward a frame destined for a unicast MAC address?

Answer: A

2.Which of the following statements describes part of the process of how a LAN switch decides to forward a frame destined for a broadcast MAC address?

Answer: C

3.Which of the following statements best describes what a switch does with a frame destined for an unknown unicast address?

Answer: A

4.Which of the following comparisons does a switch make when deciding whether to add a new MAC address to its bridging table?

Answer: B

5.In which of the following CLI modes could you configure the duplex setting for interface fastethernet 0/5?

Answer: E. The duplex command is an interface subcommand.

6.In which of the following CLI modes could you issue a command to erase the switch’s initial configuration?

Answer: B. The erase command is an EXEC command, so it cannot be issued from any configuration mode. User mode does not allow the use of the erase command.

496Appendix A: Answers to the “Do I Know This Already?” Quizzes and Q&A Questions

7.What type of switch memory is used to store the configuration used by the switch when the switch first comes up?

Answer: D. IOS loads the configuration from NVRAM into RAM during the boot sequence.

8.What command copies the configuration from RAM into NVRAM?

Answer: F. The first parameter identifies the source of the configuration, and the last parameter identifies the destination.

9.You configure the enable secret command, followed by the enable password command, from the console. You log out of the switch and log back in at the console. Which command defines the password you had to enter to access privileged mode again from the console?

Answer: B. When both are configured, the enable secret password takes precedence over the enable password.

10.What command is used on a switch to set the switch’s IP address for in-band management to 10.1.1.1, subnet mask 255.255.255.0?

Answer: A. Interestingly, the syntax matches the syntax of the same command in router IOS.

11.Imagine a 2950 switch with a PC plugged into interface fastethernet 0/1 and a router plugged into interface fastethernet 0/2. The PC needs to use TCP/IP to communicate through the router with other TCP/IP hosts. In what configuration mode could you enter the switch’s IP address?

Answer: G. First of all, the switch does not need an IP address for the PC to use TCP/IP to send packets through the switch to the router. Those details in the question were put there to help make sure you really know the answer. The ip address command is added to interface vlan 1, so the command is used in interface configuration mode for interface vlan 1.

12.What interface subcommand tells the switch to take an interface out of service?

Answer: C. The shutdown command takes the interface out of service, and the no shutdown command puts it in service again.

Chapter 1 497

Q&A

1.Describe how a switch decides whether it should forward a frame, and tell how it chooses the output interface.

Answer: The switch examines the frame’s destination MAC address and looks for the address in its bridge (or address) table. If it’s found, the matching entry tells the switch which output interface to use to forward the frame. If it isn’t found, the switch forwards the frame out all the other interfaces (except for interfaces blocked by spanning tree and the interface in which the frame was received). The switch table is built by examining incoming frames’ source MAC addresses.

2.How does a switch build its address table?

Answer: The switch listens for incoming frames and examines the source MAC address. If it isn’t in the table, the source address is added, along with the port (interface) on which the frame entered the switch. The switch also marks an entry for freshness so that entries can be removed after a period of disuse. This reduces table size and allows for easier table changes in case a spanning tree change forces more-significant changes in the switch (address) table.

3.What configuration command causes the switch to require a password from a user at the console? What configuration mode context must you be in? (That is, what command(s) must you enter before this command after entering configuration mode?) List the commands in the order you must enter them while in config mode.

Answer:

line console 0 login

The line console 0 command is a context-setting command; it adds no information to the configuration. It can be entered from any part of configuration mode. The login command, which follows the line console 0 command, tells IOS that a password prompt is desired at the console.

498Appendix A: Answers to the “Do I Know This Already?” Quizzes and Q&A Questions

4.What configuration command is used to tell the switch the password that is required at the console? What configuration mode context must you be in? (That is, what command(s) must you enter before this command after entering configuration mode?) List the commands in the order in which you must enter them while in config mode.

Answer:

line console 0 password xxxxxxx

The password command tells IOS the value that should be entered when a user wants access from the console. This value is requested by IOS because of the login command. The password xxxxxxx must be entered while in console configuration mode, which you reach by entering line console 0.

5.What command sets the password that is required after you enter the enable command? Is that password encrypted by default?

Answer: enable password or enable secret. The password in the enable command is not encrypted by default. The enable secret password is encrypted using MD5.

6.Is the password required at the console the same one that is required when Telnet is used to access a switch?

Answer: No. The Telnet (“virtual terminal”) password is not the same password, although many installations use the same value.

7.Name two commands used to view the configuration to be used at the 2950 switch’s next reload. Which one is the more-recent addition to IOS?

Answer: show config and show startup-config. show startup-config is the newer one and hopefully is easier to remember.

8.Name two commands used to view the configuration that is currently used in a 2950 switch. Which one is the more-recent addition to IOS?

Answer: write terminal and show running-config. show running-config is the newer command and hopefully is easier to remember.