Introduction to Cisco IOS CLI (Command-Line Interface)

It helped a lot, I tested it and I could see it. Thanks

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Can you please describe little bit about internal hardware structure of router and L2 & l3 switch in terms of RAm,Hardisk,ASIC and POST process.??

Hello Narad

You can find much detailed information about the internal structure of Cisco switches and how they operate at the following Cisco documentation:
An example of how how POST operates and how to use it for troubleshooting can also be found here:

I hope this has been helpful!


this is the error im facing in packet tracer . dont know if its an issue ?

Switch#erase startup-config 
Erasing the nvram filesystem will remove all configuration files! Continue? [confirm]y[OK]
Erase of nvram: complete
%SYS-7-NV_BLOCK_INIT: Initialized the geometry of nvram

hello Abdul

The Syslog message you receive is not an error but is an informational message that lets you know that the NVRAM memory has been initialized. The message is normal behavior and is not an issue.

This occurs whenever you issue the command erase startup-config or if you issue the command write erase. These essentially do the same thing.

I hope this has been helpful!


Hi Rene,

Thanks for lesson. Could you advise if this is the correct boot up process please.

  1. POST
  2. Bootstrap - located on the chip on EEPROM (ROM/ROMMON) - same as loading BIOS is copied from ROM to RAM
  3. Bootstrap decides whcih IOS to load from flash memory into RAM and then loads chosen IOS
  4. IOS fins the startup configuration rile, usually in the NVRAM and loads it into RAM as the running configuration

Are the above steps correct?


Hello Irfan

Yes, that’s correct. If you want a bit more detail, the bootstrap will decide which IOS to load based on the value of the configuration register.

I hope this has been helpful!