Router Boot Sequence

Step1: Power on Self Test (POST)

• It is an h/w test to verify that all components are operational and present.
• POST is stored and run from ROM.

  Step 2:  Load and run bootstrap code

 Bootstrap code is used to execute subsequent programs.

• Finds the IOS s/w, loads and run it.
• Not used until next time router is reloaded.

 Step2.1: Find the IOS software 

• Bootstrap code finds the IOS image /software from the flash memory by default.
• Configuration register and configuration file in the NVRAM help determine IOS image. 

Step.2.2: Load the IOS software 

• Bootstrap code loads   the IOS image into RAM and starts IOS running. 

Step 3: Find the configuration 

• By default IOS looks in NVRAM for a valid configuration file.
• File is called start-up configuration.
• If no configuration exists or is ignored, router enters in to setup mode.