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
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
Find and apply the
configuration statements about the router,
including protocol functions and interface
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 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
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
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
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
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
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
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
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
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
If the router cannot find a
configuration file, the router enters setup
The router stores a backup
copy of the new configuration from setup mode in
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