Router Setup And  Startup

In the "Router Components" chapter, you learned the correct procedures and commands to access a router, examine and maintain its components, and test its network connectivity. In this chapter, you will learn how to start a router for the first time by using the correct commands and startup sequence to do an initial configuration of a router. In addition, this chapter explains the startup sequence of a router and the setup dialog that the router uses to create an initial configuration file.

Router startup routine

A router initializes by loading the bootstrap, the operating system, and a configuration file. If the router cannot find a configuration file, then it enters setup mode. The router stores, in NVRAM, a backup copy of the new configuration from setup mode.

The goal of the startup routines for Cisco IOS software is to start the router operations. The router must deliver reliable performance in its job of connecting the user networks it was configured to serve. To do this, the startup routines must:

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

  • Find and load the Cisco IOS software that the router uses for its operating system.

  • Find and apply the configuration statements about the router, including 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 from ROM on all hardware modules. These diagnostics verify the basic operation of the CPU, memory, and network interface ports. After verifying the hardware functions, the router proceeds with software initialization.

Router startup sequence

After the power-on self test on the router, the following events occur as the router initializes:

Step 1 -- The generic bootstrap loader, in ROM, executes on the CPU card. A bootstrap is a simple, preset operation to load instructions that in turn cause other instructions to be loaded into memory, or cause entry into other configuration modes.

Step 2 -- 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.

Step 3 -- The operating system image is loaded. Then, when it is loaded and operational, the operating system 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 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, also called the setup dialog.

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

Commands related to router startup

The top two commands in the Figure -- show startup-config and show running-config -- display the backup and active configuration files. The erase startup-config command deletes the backup configuration file in NVRAM. The reload (reboot) command reloads the router, causing it to run through the entire startup process. The last command, setup, is used to enter setup mode from the privileged EXEC prompt.

* Note: The commands show config, write term, and write erase, used with Cisco IOS Release 10.3 and earlier, have been replaced with new commands. The old commands continue to perform their normal functions in the current release, but are no longer documented. Support for these commands will cease in a future release.

Using the setup command

One of the routines for initial configuration is the setup mode. As you've already learned in this lesson, the main purpose of the setup mode is to bring up, quickly, a minimal configuration for any router that cannot find its configuration from some other source.

For many of the prompts in the system configuration dialog of the setup command facility, default answers appear in square brackets [ ] following the question. Press the Return key to use these defaults. If the system has been previously configured, the defaults that will appear will be the currently configured values. If you are configuring the system for the first time, the factory defaults will be provided. If there is no factory default, as in the case of passwords, nothing is displayed after the question mark [?]. During the setup process, you can press Control+C at any time to terminate the process and start over.

When you complete the configuration process in setup mode, the screen will display the configuration that you have just created. You will then be asked whether you want to use this configuration. If you enter "yes", the configuration will be executed and saved to NVRAM. If you answer "no", the configuration will not be saved and the process will begin again.

If a --More-- prompt appears, press the space bar to continue

Setting up global parameters

After viewing the current interface summary, a prompt will appear on your monitor, indicating that you are to enter the global parameters for your router. These parameters are the configuration values you select.

A prompt appears on your monitor, as illustrated in Figure . It indicates that you are to enter the global parameters that you set for your router. These parameters are the configuration values you decided on.

The first global parameter allows you to set the router host name. This host name will be part of the Cisco IOS prompts for all configuration modes. At initial configuration, the router name default will be displayed between square brackets as [Router].

Use the next global parameters shown in the graphic to set the various passwords used on the router. You must enter an enable password. When you enter a string of password characters for the prompt, "Enter enable secret"; the characters are processed by Cisco proprietary encryption. This enhances the security of the password string. Whenever anyone lists the contents of the router configuration file, this enable password appears as a meaningless string of characters.

Setup recommends, but does not require, that the "enable password" be different from the "enable secret word". The "enable secret word" is a one-way cryptographic secret word that is used instead of the "enable password" when it exists. The "enable password" is used when no "enable secret word" exists. It is also used when using older versions of the IOS.

When you are prompted for parameters for each installed interface, as shown in Figure , use the configuration values that you have selected for your router. Whenever you answer yes to a prompt, additional questions may appear regarding the protocol.


The router initializes by loading a bootstrap, the operating system, and a configuration file.

If the router cannot find a configuration file, the router enters setup mode.

The router stores a backup copy of the new configuration from setup mode in NVRAM.

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