Answer / shahin

Default boot sequence for Cisco IOS software:

1. NVRAM
2. Flash (Sequentail)
3. TFTP (Network Boot)
4. ROM (partial IOS)


Cisco routers can boot Cisco IOS software from these locations:

1. Flash memory
2. TFTP server
3. ROM (not full Cisco IOS)

Answer / jitendera kumar sinha

actauly in there are 4 option and each option conatin 3
sequance
i mark
nvram-------flash-----post rom

am i write?
please give feedback

Answer / shahin

Hi Jitendera,

When the router boots, it looks for the boot command stored
in NVRAM which is By default "boot system flash" means boot
from flash

then the router loads the IOS from flash.

If it is unable to load IOS from Flash, then it goes for
TFTP server then ROM etc


So during boot, Router goes to -

NVRAM > Flash > TFTP > ROM.



I think i made it clear.

Answer / deepak

Boot Process


ROM - bootstrap

- the system bootstrap routine starts from ROM and tells the
router to run the POST and then look for an IOS in Flash memory

- router runs the POST (Power-On Self Test)
FLASH ( IOS--->DRAM)

- looks for a compressed IOS image in Flash Memory

· if an IOS is found, it is decompressed and loaded
into DRAM

· if no IOS is found the bootstrap routine can either
load an image from a TFTP server or from the included CD
that come with the router
NVRAM (Config--->DRAM)

- the router looks to NVRAM for a startup config

· if a startup config is found in NVRAM it is loaded
into DRAM

· if there is no startup config in NVRAM, then the
router goes into *setup mode

DRAM (ARP cache and routing tables)

- the DRAM is now loaded with the IOS and config, and the
router sends out ARP’s and Routing protocol broadcasts to
build it’s ARP cache and routing tables and store them in
DRAM. This is now the operating memory of the router. All
other types of memory are fairly dormant from this point on.



* setup mode is an interactive, step-by-step process with
only very basic global commands. You can enter setup mode
at any time from priviledged mode by typing “setup”. There
are two versions: Basic Management and Extended Setup

Answer / nikhil maggu

bhaio NVRAM me jane se pehle POST(Power on Self test) bhi
hota h(generally ye specify nahi karte);just for knowledge m
sharing this,so the complete sequence will be :

POST > NVRAM > Flash > TFTP > ROM.

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