Managing IOS files & Device Details

RAM - Stores running configuration "working memory"
Flash - Holds the Cisco IOS software
ROM - location of bootstrap program and ROMMON recovery IOS
NVRAM - stores start up configuration

Cisco Boot Order

  1. POST (Power on Self Test)
  2. Copies Rom bootstrap to RAM and runs bootstrap program
  3. bootstrap decides which IOS to load
  4. Copies start-up config to running config
Configuration register for ROMMON is 0x2100

How a router chooses which OS to load
  1. the last hex digit in the configuration register (bootfield)
  2. any boot system global config in start up
Modern Routr bootfield options
  1. if bootfield = 0, use ROMMON oS
  2. if bootfield = 1, load first os in flash
  3. if boot field = 2-fi
    1. try boot system in startup until one works 
    2. if all boot systems fail load first OS in flash