Router Components: ROM

1
Router Components ROM

• Read-only memory (ROM)
• Stores
• the bootstrap program, also called the ROM
  Monitor, that initializes the routers basic
  hardware components.
• POST (power-on self test), that checks the basic
  functionality of the router hardware and
  determines interfaces.
• Mini-IOS, which is used to bring up an interface.
• ROM monitor mode
• Router mode that allows to configure your router
  in the event that there is no valid IOS file on
  your flash memory

2
Router Components RAM
RAM stores following components
RAM
(2) Internetwork Operating System (IOS) The IOS
is located by the bootstrap program, it is loaded
in to RAM
(3) Command Executive Commands are loaded.

• Programs
• POST and bootstrap to test the equipment
• and locate the IOS

(4) Running Config. File the IOS loads active
configuration file (usually from NVRAM)
(5) Tables ARP and routing tables
(6) Buffers used for routing incoming and
outgoing packets
3
Router Components NVRAM

• Nonvolatile random access memory (NVRAM)
• Special type of RAM
• Not cleared when the router is rebooted
• Startup configuration for the router is stored in
  NVRAM by default
• Stores all the user-defined configuration
  information for the router

4
Router Components Flash Memory

• Erasable, programmable, read-only memory (EPROM)
• Not typically modified during normal operations
• Can be upgraded or erased when necessary
• Content of flash memory is maintained even when
  the router is rebooted

5
Show Commands
Rshow flash
Rshow version
Rshow interfaces
RAM
NVRAM
Flash
Internetwork Operating System
Backup Configuration File
Operating Systems
Interfaces
Programs
Running Configuration
Table and Buffers
Rshow process CPU Rshow protocols
Rshow mem Rshow stacks Rshow buffers
Rshow startup-config
Rshow running-config Rwrite term
6
Startup
7
Managing Configuration Registers

• 16-bit software register, which is written into
  NVRAM.
• By default, it is set to load IOS from flash
  memory and look for startup-configuration from
  NVRAM.
• ..\Calc\config_register.exe

8
Checking Current Configuration
9
Chancing the Configuration Register

• Router(config)config-register 0x101.
• Recovering Passwords pp. 356-359