Cisco CCNA: Powering on Cisco routers. Boot process explained, from start to finish.

It is very easy for one to know how to use a Cisco router
without knowing the various stages involved during its boot process. As a
network engineer, it is required of you to understand these stages, not just
for certification exam purposes but to help in your career as a network
engineer. In this post, I will share with us the various stages of the router’s
boot process and the events that happen at each stage.

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 Points to note about the router:
>> Routers are layer
3 devices
>> Routers break up
broadcast by default
Routers perform the following functions on a network:
>> Path
>> Packet switching
>> Packet
The router’s boot
When a router is power up,
it goes through the following boot process:
>> Power On
Self Test (POST):
involves checking the various hardware components of the router to determine
if they are all in good working condition. If the POST process fails, the boot
sequence ends there, but if all components are found to be okay, then it
proceeds to the next stage.

>> Load a
valid ios from flash:
passing the POST, the router looks for a valid internetworking operating system
(ios) stored in flash memory and loads it. The router has specific instructions
that tell it to check the flash memory for the ios file. The instructions can
be altered to make the router boot from a TFTP server or a USB, depending on
the model of router. After loading a valid ios from the flash memory, the
router looks for a valid configuration file.
>> Valid
configuration in NVRAM:
stage is where the router looks for a valid configuration file stored in
non-volatile random access memory (NVRAM). The file is called the start-up
configuration. When it is found and loaded into RAM, that copy held in RAM becomes
the running configuration.
In conclusion, there are
three stages involved in a router’s boot process: Post, loading ios from flash,
and loading a running configuration from NVRAM. The router has specific
instructions stored in the configuration register that direct the boot process
on what memory to contact at every stage of the boot operation. 

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Ashioma Michael, a BSc (Computer Science)., MTCNA, CCNA, and CCNP holder with many years of industry-proven experience in network design, implementation and optimization. He has tutored and guided many professionals towards obtaining their Cisco certifications. Mike works as a senior network engineer with one of the leading internet service providers in West Africa.

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