The Internal Components of a Cisco Router and Switch

The Internal Components of a Cisco Router and Switch

Bootstrap
Bootstrap is stored in the microcode of the ROM, the bootstrap is bringing a router up during initialization. It will boot the router and then load the IOS.

POST
POST (power-on-self-test) is stored in the microcode of the ROM, the POST is used to check the basic functionality of the router hardware and determine which interfaces are present.

ROM monitor
ROM monitor stored in the microcode of the ROM monitor is used for manufacturing, testing, and troubleshooting.

Mini-IOS
Mini-IOS called the RXBOOT or boot loader by Cisco, the mini-IOS is a small IOS in ROM that can be used to bring up an interface and load a Cisco IOS into flash memory. The mini-IOS can also perform a few other maintenance operations.

RAM
RAM (randomly used to hold packet buffers, ARP cache, routing table, and also access memory) is the software and data structure that allows the router to function. Running configuration is stored in RAM, and most routers expand the IOS from flash into RAM upon boot.

ROM
ROM (read-only memory) is used to start and maintain the router. Hold the POST and the bootstrap program, as well as the mini-IOS. Flash memory stores the Cisco IOS by default. Flash memory is not erased when the router is reloaded. It is EEPROM (electronically erasable programmable read-only memory) created by Intel.

NVRAM
NVRAM (nonvolatile RAM) is used to hold the router and switch configuration. NVRAM is not erased when the router or switch is reloaded and does not store an IOS. The configuration is stored in NVRAM.

Configuration register
Configuration register used to control how the router boots up. This value can be found as the last time of the show version command output and by default is set to 0x2102, which tells the router to load the IOS from flash memory as well as to load the configuration from NVRAM.

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