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CCNA 2: Routers and Routing Basics v3.1 Instructor Guide – Module 5
Copyright
©
2004, Cisco Systems, Inc.
5.1 Router Boot Sequence and Verification
Essential Labs:
5.1.3 and 5.1.5
Optional Labs:
None
Core TIs:
All
Optional TIs:
none
Course-Level Claim:
Students can Identify the stages of the router boot-up sequence and
show how
the configuration-register
and
boot system
commands modify that
sequence.
Certification-Level Claim:
Students can describe the components of network devices.
Hands-on skills:
none
5.1.1 Stages of the router power-on boot sequence
The purpose of the router boot-up sequence is to verify the operation of hardware and load the
correct IOS and configuration file. The router must follow a predefined set of steps while it
boots up:
•
When the router is first powered-on, it executes the power-on self test (POST).
These diagnostics are located in ROM and verify the proper operation of the router
hardware.
•
If the router passes the POST, the bootstrap loader in ROM executes. The
bootstrap basically indicates a starting point in memory that will load other
instructions.
•
Now the router is ready to load the operating system, which is Cisco IOS. The IOS
can be found in flash, TFTP, or ROM. The boot field of the configuration register
will indicate the location of the IOS image.
•
After the operating system is loaded and operational, the configuration file from
NVRAM is loaded and executed. If no configuration file exists in NVRAM, the
router will prompt the user to use a question-driven setup menu.
Review the figure in this TI with the students. This is an excellent visual representation of the
different aspects of the boot process. Each student should be able to reproduce this figure
from memory. Remove the configuration from NVRAM to demonstrate the process used to
check for a TFTP server and then enter the setup menu. Demonstrate the use of
Ctrl
-
C
to exit
from the setup menu.
5.1.2 How a Cisco device locates and loads the Cisco IOS
The router can load the Cisco IOS from several different locations that can be specified by the
operator. The
boot system
commands can be used to identify a fallback sequence of
locations to look for the IOS.