Basic Router Configuration

What are the Internal Components of a Router? Most of the components in a router are hardware.

Major Components of a Router The major components of the router are shown in the image.

The following table lists the description of each of these components: Component

Description

RAM

Random access memory contains the software and data structures that allow the router to function. The principle software running in RAM is the Cisco IOS image and the running configuration.

ROM

Read-only memory contains microcode for basic functions to start and maintain the router.

Flash memory

Flash is primarily used to contain the IOS software image. Some routers run the IOS image directly from Flash and do not need to transfer it to RAM.

NVRAM

Non-volatile random access memory is mainly used to store the configuration. NVRAM uses a battery to maintain the data when power is removed from the router.

Configuration Register

The configuration register is used to control how the router boots up.

Interfaces

The physical connections to the external world for the router. These interfaces include the following types: • • • • • •

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Ethernet and Fast Ethernet Asynchronous and synchronous serial Token Ring FDDI ATM Console and auxiliary ports

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Stages of the Router Power On/Bootup Sequence The sequence of events that occurs during the power-up or the booting of a router is important to understand. Knowledge of this sequence can assist in accomplishing operational tasks and troubleshooting router problems. Order of Router Bootup Events

When power is initially applied to a router, events occur in a particular process order:

Router Bootup Process Table The following table summarizes the router bootup process. Step

Stage

What Happens

1.

Power On Self Test (POST)

This event is a series of hardware tests to verify that all components of the router are functional. During this test the router also determines what hardware is present. POST executes from microcode resident in the system ROM.

2.

Load and run bootstrap code

Bootstrap code is used to perform subsequent events like finding the IOS software, loading it, and then running it. Once the IOS software is loaded and running, the bootstrap code is not used until the next time the router is reloaded or power cycled.

3.

Find the IOS software

The bootstrap code determines where the IOS software to be run is located. The configuration register, configuration file, or Flash memory are the normal places to house the IOS image. Where and what image file to use can be configured.

4.

Load the IOS software

Once the bootstrap code has found the proper image, it then loads that image into RAM and starts the IOS running. Some routers do not load the IOS image into RAM, but execute it directly from Flash memory.

5.

Find the configuration

The default is to look in NVRAM for a valid configuration.

6.

Load the configuration

The desired configuration for the router is loaded and executed. If no configuration exists the router will enter the setup utility or attempt an autoinstall.

7.

Run

The router is now running the configured IOS.

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Starting a Router This lesson describes the initial configuration for a Cisco router

Initial Startup of Cisco Routers This section covers startup and initial configuration of a Cisco IOS router.

How Startup Routines Start Operations To start router operations, the startup routines must: 1. Make sure that the router finds tested hardware. 2. Find and load the Cisco IOS software that the router uses for its operating system. 3. Find and apply the configuration statements about router-specific attributes, protocol functions, and interface addresses. When a Cisco router powers up, it performs a Power-On Self Test (POST). During this self test, the router executes diagnostics to verify the basic operation of the CPU, memory, and interface circuitry.

After verifying the hardware functions, the router proceeds with software initialization.

Examining the Initial Bootup Output from the Router

Some startup routines act as fallback operations that are able to perform the router startup should other routines be unable to do so. This flexibility allows Cisco IOS software to start up in a variety of initial situations.

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. This special mode is also called the setup dialog.

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Examining Router Login After you have configured a router from the setup utility, you will reconfigure or add to the configuration from the user interface that runs on the router console or terminal. You can also configure Cisco routers using remote access. This topic discusses the access levels and the user mode command list. Access Levels

As discussed earlier, for security purposes, the EXEC has two levels of access to commands: •

User mode - Typical tasks include those that check the router status.

•

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

When you first log in to the router, you will see a user-mode prompt. EXEC commands available in user mode are a subset of the EXEC commands available in privileged mode. For the most part, these commands allow you to display information without changing router configuration settings. To access the full set of commands, you must first enable privileged mode with the enable command and supply the enable secret password. Your EXEC prompt will then show as a pound sign (#) while you are in this mode.

From the privileged level, you can also access global configuration mode and the other specific configuration modes. These modes include interface, sub-interface, line, router, route-map, and several others. What are the CLI Command Modes?

The first method of configuration presented was the setup utility. Setup allows a basic initial configuration to be created. For more complex and specific configurations, we can use the command line interface to enter terminal configuration mode. Accessing the Modes

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From the privileged EXEC mode you can enter global configuration mode with the configure terminal command. From the global configuration mode, you have access to the specific configuration modes, which include: • • • • • •

Interface - Supports commands that configure operations on a per-interface basis Subinterface - Supports commands that configure multiple virtual interfaces on a single physical interface Controller - Supports commands that configure controllers (for example E1 and T1 controllers) Line - Supports commands that configure the operation of a terminal line Router - Supports commands that configure an IP routing protocol IPX-router - Supports commands that configure the Novell network-layer protocol

Common CLI Error Messages Console error messages help you identify problems with an incorrect command entry. Error messages that you might encounter while using the command line interface include the following:

Error message

Message Meaning

% Ambiguous You did not enter enough command: "show characters for your device to recognize the con" command.

How to Get Help Reenter the command followed by a question mark (?) with no space between the command and the question mark. The possible keywords that you can enter with the command are displayed.

% Incomplete command.

You did not enter all of the Reenter the command followed by a question mark (?) keywords or values with a space between the command and the question required by this command. mark.

% Invalid input detected at '^' marker.

You entered the command Enter a question mark (?) to display all of the incorrectly. The caret (^) commands or parameters that are available in this marks the point of the mode. error.

Viewing the Configurations The show running-config and show startup-config commands are among the most used Cisco IOS software EXEC commands. They allow an administrator to see the current running configuration in RAM on the router or the startup configuration commands in NVRAM that the router will use on the next restart.

Recognizing the Active and Backup Configurations Confusion can sometimes occur between these two commands. Learning to recognize what you are viewing will help.

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You will know that you are looking at the active configuration file when you see the words "Current Configuration" at the top of the display.

To do. • • • •

You will know that you are looking at the backup configuration file when you see a message at the top telling you how much nonvolatile memory has been used.

Show Copy Hostname Password

Configuring Router Passwords You can secure your router by using passwords to restrict access. Passwords can be established both on individual lines and to the privileged EXEC mode. Passwords are case sensitive. Procedure for Configuring Router Passwords The procedure outlined in the following table describes how to configure passwords on a router.

Step Action 1.

Set the login password on the console terminal by using the line console 0 command followed by the login and password subcommands.

Results and Notes The number in the configuration specifies the single console port; the port is number 0.

Router(config)#line console 0 Router(config-line)#login Router(config-line)#password cisco 2.

Set a login password on incoming Telnet sessions by using the line vty 0 4 command followed by the login and password subcommands .

The numbers 0 4 specify the number of Telnet sessions allowed in the router. You can also set up a different password for each line by using the line vty port number command.

Router(config)#line vty 0 4 Router(config-line)#login Router(config-line)#password sanjose

3.

Set restricted access to the privileged EXEC mode using the enable password global command.

Disable the privileged EXEC mode password using the no enable password command.

Router(config)#enable password cisco 4.

Set an encrypted form of the enable password called the enable secret password by entering the enable secret command at the global configuration mode prompt.

Disable the encrypted password using the no enable secret command. Note - If you configure the enable secret password, it is used instead of the enable password, not in addition to it.

Router(config)#enable secret sanfran 5.

Set other password encryptions to add a further layer of security to the router passwords using the service password-encryption command. Router(config)#service password-encryption set passwords here

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This command is particularly useful for passwords that cross the network or are stored on a TFTP server. Disable the encryption on the passwords using the no service password-encryption command.

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