Router Fundamentals

Router Fundamentals

The startup routines for Cisco IOS Software have the goal of starting router operations. The router uses information from the configuration file when it starts up. The configuration file contains commands to customize router operation. As you saw in Chapter 10, "WANs and Routers," if no configuration file is available, the system configuration dialog setup guides you through creating one. The router must deliver reliable performance connecting the user networks that it was configured to serve. To do this, the startup routines must do the following:

· Make sure that the router comes up with all its hardware tested.

· Find from memory and load the Cisco IOS Software image that the router uses for its operating system.

· Find from memory and apply the configuration statements about the router, including protocol functions and interface addresses.

The router makes sure that it comes up with tested hardware. When a Cisco router powers up, it performs a power-on self-test (POST). During this self-test, the router executes diagnostics from ROM on all modules. These diagnostics verify the basic operation of the CPU, memory, and network interface ports. After the router verifies the hardware functions, it proceeds with software initialization. You configure Cisco routers from the user interface that runs on the router console or terminal. You also can configure Cisco routers by using remote access. You must log in to the router before you can enter an EXEC command. For security purposes, the router has two levels of access to commands:

· User mode—Typical tasks include those that check the router status. In this mode, router configuration changes are not allowed.

· Privileged mode—Typical tasks include those that change the router configuration.

Concept Questions

Demonstrate your knowledge of these concepts by answering the following questions in the space provided.

1. Configuration files can come from the console, NVRAM, or a TFTP server. What are the different router modes?

· Privileged mode is used for copying and managing entire configuration files.

· Global configuration mode is used for one-line commands and commands that change the entire router.

· Other configuration modes are used for multiple command lines and detailed configurations.

2. What does it mean to configure a router?

Router configuration information can be generated by several means. You can use the privileged EXEC configure command to configure from a virtual (remote) terminal, a modem connection, or a console terminal. This enables you to enter changes to an existing configuration at any time.

You can also use the privileged EXEC configure command to load a configuration from a network TFTP server, which enables you to maintain and store configuration information at a central site.

3. Why must routers be configured?

A router must know which interfaces are to be used, which routed and routing protocols are supported, along with security and access list configurations.

4. The router initializes by loading a bootstrap, the operating system, and a configuration file. What does each of these items do?

A bootstrap is a simple, preset operation to load instructions that, in turn, cause other instructions to be loaded into memory or that affect entry into other configuration modes.

The operating system (Cisco IOS) can be found in one of several places. The location is disclosed in the boot field of the configuration register. If the boot field indicates a Flash, or network load, boot system commands in the configuration file indicate the exact location of the image.

The configuration file saved in NVRAM is loaded into main memory and is executed one line at a time. These configuration commands start routing processes, supply addresses for interfaces, set media characteristics, and so on.

5. If the router cannot find a configuration file, the router enters setup mode. What does the setup mode do?

If no valid configuration file exists in NVRAM, the operating system executes a question-driven initial configuration routine referred to as the system configuration dialog, or setup dialog.

Setup is not intended as the mode for configuring complex protocol features in the router. You should use setup to bring up a minimal configuration, and then use various configuration-mode commands rather than setup for most router configuration tasks.

6. The router stores a backup copy of the new configuration from setup mode. Where does the router store this backup copy?

The router stores in NVRAM a backup copy of the current configuration.

7. Prepare a flowchart of the startup (boot) sequence of a multimedia PC.

Refer to the Companion Guide.

8. You can use the router to do the following: log in with the user password, enter privileged mode with the enable password, disable, or quit. What procedures would you follow to log in to the router?

When you first log in to a router, you see a user-mode prompt:

Router>

At the > prompt, type enable

At the password prompt, enter the password that has been set with the enable secret command.

When you have completed the login steps, the prompt changes to a pound sign (#) because you are now in privileged mode. From privileged mode, you can access modes such as global configuration mode and other specific configuration modes.

Logging in to and out of the Router

Router con0 is now available.

Press RETURN to get started.

User Access Verification

Password:

Router>

Router> enable

Password:

Router#

Router# disable

9. You can use the following advanced help features: Command completion, command prompting, and syntax checking. Why would you need to use syntax checking?

You can use the following advanced editing features:

Þ Automatic line scrolling

Þ Cursor controls

Þ History buffer with command recall

Þ Copy and paste, which are available on most laptop computers

10. Why is it important to have two different levels of command access?

Commands available at user level are a subset of the commands available at the privileged level. For the most part, these commands enable you to display information without changing router configuration settings. You may want to have multiple administrators with varied levels of access. To access the full set of commands, you must first enable privileged mode.

Vocabulary Exercise

Define the following terms as completely as you can. Refer to the online curriculum or Chapter 11 from the Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Third Edition, for help.

Configure terminal—Command used to configure manually from the console terminal.

CPU (central processing unit)—The part of a computer that controls all the other parts. It fetches instructions from memory and decodes them. This may cause it to transfer data to or from memory or to activate peripherals to perform input or output.

erase startup-config—Command used to delete the backup configuration file in NVRAM.

Privileged mode—Typical tasks include those that change the router configuration.

Reload—The event of a Cisco router rebooting, or the command that causes the router to reboot.

User mode—Typical tasks include those that check the router status. In this mode, router configuration changes are not allowed.

Focus Questions

1. How do you access a router?

To configure Cisco routers, you must either access the user interface on the router with a terminal or access the router remotely. When accessing a router, you must log in to the router before you enter any other commands.

2. Distinguish between user mode and privileged mode.

User mode enables you to check router status; privileged mode enables you to actually change the router’s configuration.

3. What does it mean to configure a router? Why must routers be configured?

Configuring a router usually describes the process by which a router learns its Layer 3 addresses, hostname, passwords, support protocols. A router must know which interfaces are to be used, which routed and routing protocols are supported, along with security and access list configurations.

4. What do the prompts for user EXEC mode, privileged EXEC mode, and global configuration mode look like?

Router>, Router#, and Router(config)#

5. What are two basic tasks when first configuring a router?

Password configuration and naming the router (router identification configuration).

6. In Cisco IOS Software, what is the user mode prompt and what is the privileged mode prompt?

The > is the user-mode prompt; the # is the privileged-mode prompt.

7. What must you type at the user or privileged mode prompts to display a list of commonly used commands?

You must type a ? to display the list of commonly used commands.

8. When in user mode, what must you do to enter privileged mode?

You must type ena (short for enable) and then a password.

9. If you are unsure of the syntax or arguments for a command, what feature can be of great help to you?

If you guess at the command syntax and arguments, the Cisco IOS context-sensitive help will highlight your errors and suggest corrections. Additionally, by adding a space and then the question mark after a partial command, you will get hints about how to proceed.

10. What are the three main things the router accomplishes upon startup?

Þ Makes sure that the router comes up with all its hardware tested.

Þ Finds and loads the Cisco IOS Software that the router uses for its operating system.

Þ Finds the startup-config file and applies the configuration statements, including protocol functions and interface addresses.

11. Briefly describe the router startup sequence.

Step 1. The generic bootstrap loader executes on the CPU card.

Step 2. The location of the IOS image is found by searching the configuration registers, If the boot field indicates a Flash, or network load, boot system commands in the configuration file indicate the exact location of the image.

Step 3. The operating system image is loaded. Once operational, the OS locates the hardware and software components and lists the results on the console terminal

Step 4. The configuration file saved in NVRAM is loaded into main memory and is executed one line at a time. These configuration commands start routing processes, supply addresses for interfaces, set media characteristics, and so on.

Step 5. If no valid configuration file exists in NVRAM, the operating system executes a question-driven initial configuration routine referred to as the system configuration dialog, or setup dialog.

12. What is the main purpose of setup mode?

The main purpose of setup mode is to quickly bring up a minimal configuration for any router that cannot find its configuration from some other source.

13. During the system configuration dialog, you are prompted to set up “global parameters” and to set up “interfaces.” Explain.

Global parameters are used to configure hostnames, enable passwords, enable secret passwords, and global configuration values. When prompted to set up “interfaces,” you need to use the configuration values that you have determined for each interface. These values include IP address, subnet mask, network protocol, and so on.

14. After you have completed the setup command program and your configuration displays, you are asked whether you want to use this configuration. If you answer “yes,” what happens?

If you answer “yes,” the configuration is executed and saved to NVRAM. Your system is now ready to use.
CCNA Exam Review Questions

The following questions help you review for the CCNA exam. Answers appear in Appendix B, "CCNA Exam Review Questions Answer Key."

1. What are the two modes of access to router commands for Cisco routers?

A. User and privileged

B. User and guest

C. Privileged and guest

D. Guest and anonymous

2. Why are there two modes of access to router commands on Cisco routers?

A. One mode is for remotely working on the router, whereas the other mode is for directly working on the router via a console.

B. One mode, which has many automatic sequences, is for new users, whereas the other mode is for experienced users who can issue direct commands.

C. One mode lets a number of users see what's happening on the router, whereas the other mode lets a few users change how the router operates.

D. One mode is for the initial router configuration and startup, whereas the other mode is for maintaining, updating, and changing the router after initial startup.

3. What can be done only in privileged mode on Cisco routers?

A. Change the configuration.

B. Enter commands.

C. Check routing tables.

D. Monitor performance.

4. How do you switch from user to privileged mode on Cisco routers?

A. Type admin and enter a password.

B. Type root and enter a password.

C. Type enable and enter a password.

D. Type privileged and enter a password.

5. What happens if you type enable on a Cisco router user interface?

A. You switch to user mode.

B. The last command entered is activated.

C. A new LAN is added to the router table.

D. You switch to privileged mode.

6. Which of the following commands is not available in the user access mode?

A. show

B. ppp

C. trace

D. ping

7. Which of the following is the user-mode prompt for Cisco router user interfaces?

A. #

B. >

C. <

D. |#

8. Which of the following is the privileged-mode prompt for Cisco router user interfaces?

A. #

B. >

C. <

D. |#

9. How do you log out of a Cisco router user interface?

A. Type Control-Q.

B. Type quit.

C. Type exit.

D. Type Control-X.

10. How can you get a list of commonly used commands from a Cisco router user interface?

A. Type list.

B. Type Control-C.

C. Type Control-?.

D. Type ?.

11. What does the "More" prompt at the bottom of a screen on a Cisco router user interface mean?

A. Multiple screens are available as output.

B. Additional detail is available in the manual pages.

C. Multiple entries are required in the command.

D. Additional conditions must be stated.

12. How do you get to the next screen if "More" is indicated at the bottom of the current screen on a Cisco router user interface?

A. Press the Page Down key.

B. Press the spacebar.

C. Press the End key.

D. Press the Tab key.

13. Which keystroke(s) automatically repeat(s) the previous command entry on a Cisco router user interface?

A. Left arrow

B. Right arrow

C. Ctrl-R

D. Ctrl-P

14. What happens if you press ? in a Cisco router user interface?

A. You see all users logged in to the router.

B. You list the last command you typed.

C. You enter the help system.

D. You find out which mode you are currently in.

15. What does it mean if you see the symbol ^ on a Cisco router user interface?

A. There is an error in the command string.

B. You are in Help mode.

C. You must enter more information to complete the command.

D. You are in privileged mode.

16. What would you type at the router user prompt if you wanted to see which show subcommands were available?

A. ?

B. command ?

C. show ?

D. list ?

17. What would you type at the router user prompt if you wanted to see which configuration subcommands were available?

A. ?

B. command ?

C. list ?

D. config ?

18. Which of the following commands is only available at the privileged access mode?

A. ping

B. show

C. trace

D. ppp

19. Which of the following is the correct order of steps in the Cisco router system startup routine?

A. Locate and load the operating system, load the bootstrap, test the hardware, and locate and load the configuration file.

B. Test the hardware, load the bootstrap, locate and load the operating system, and locate and load the configuration file.

C. Load the bootstrap, locate and load the configuration file, test the hardware, and locate and load the operating system.

D. Test the hardware, load the bootstrap, locate and load the configuration file, and locate and load the operating system.

20. Which of the following is not a step in the Cisco router system startup routine?

A. Loading the bootstrap

B. Power-up hardware self-test

C. Enabling CDP on each interface

D. Locating and loading the configuration file

21. Which of the following is an important function of POST?

A. Determining the router hardware and software components and listing them on the console terminal

B. Causing other instructions to be loaded into memory

C. Executing diagnostics that verify the basic operation of router hardware

D. Starting routing processes, supplying addresses for interfaces, and setting up media characteristics

22. Which of the following is an important result of Cisco IOS Software loading onto a router?

A. Determining the router hardware and software components and listing them on the console terminal

B. Causing other instructions to be loaded into memory

C. Executing diagnostics that verify the basic operation of router hardware

D. Starting routing processes, supplying addresses for interfaces, and setting up media characteristics

23. Which of the following is an important result of the configuration file loading onto a router?

A. Determining the router hardware and software components and listing them on the console terminal

B. Causing other instructions to be loaded into memory

C. Executing diagnostics that verify the basic operation of router hardware

D. Starting routing processes, supplying addresses for interfaces, and setting up media characteristics

24. Which of the following is not a function of the router system startup routine?

A. Verifying the routing of protocol packets

B. Testing of the basic operations of router hardware

C. Causing other instructions to be loaded into memory

D. Starting routing processes, supplying addresses for interfaces, and setting up media characteristics

25. When is the router setup mode executed?

A. After the saved configuration file is loaded into the main memory

B. When the network administrator needs to enter complex protocol features on the router

C. When the router begins software initialization

D. When the router cannot find a valid configuration file

26. Which of the following does not describe features of the router setup mode?

A. Many default settings appear in square brackets.

B. The prompt and command for the setup mode are "router# setup".

C. The first line and title of the setup dialog is "System Configuration Dialog".

D. Pressing the Enter key cancels dialog prompts.

27. Which of the following correctly describes a procedure for setup of router global and interface parameters on a router?

A. A default parameter is shown in square brackets at every prompt.

B. The router host name must be set.

C. An enable secret password can be set, but it is not required.

D. For each installed interface, a series of questions must be answered.

28. Which of the following does not correctly describe a procedure for setup of global and interface parameters on a router?

A. An enable secret password must be entered.

B. A default parameter is shown in square brackets at every prompt.

C. Configuration values that you have determined for the installed interfaces are entered as parameters at the interface prompts.

D. The router hostname must be set.

29. What information do you need to gather before starting a global or interface configuration session on a router?

A. Brand and model of router and type of networks the router connects to directly

B. Cisco IOS Software version and current register setting

C. Which routing protocols will be needed, IP addresses of interface and subnets, and which interfaces are being used

D. IP addresses of neighboring routers and size of Flash memory

30. Which of the following correctly describes the router setup script review?

A. The setup command program displays the configuration that was created from your answers to the setup prompts.

B. The setup command program asks you whether you want to change any of your answers.

C. If you choose to use the displayed configuration, you select a location to save it to.

D. If you choose not to use the configuration, you must reboot the router.

31. Which of the following correctly describes the procedure for modifying the script displayed upon completion of the router configuration process?

A. The setup command program prompts you at each of the script lines as to whether you want to change your answers.

B. When you choose not to accept the configuration, the router reboots.

C. When you select the dialog lines that you want to change, the program prompts you again at those lines.

D. The script tells you to use configuration mode to modify the configuration.