Components of Router
Router components:
To configure and troubleshoot a Cisco internetwork, you need to know the major components of Cisco routers and understand what each one does.
1-Bootstrap Stored in the ROM, It will boot the router and then load the IOS.
2-POST (power-on self-test) Stored in the ROM, the POST is used to check the basic functionality of the router hardware and determines which interfaces are present.
3-ROM monitor Stored in the ROM, the ROM monitor is used for manufacturing, testing, and troubleshooting.
4-Mini-IOS Called the RXBOOT or bootloader 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. Mini-IOS is not present on every router.
5-RAM (random access memory) Used to hold ARP cache, routing tables, software and data structures that allow the router to function. Running-config is stored in RAM, and most routers loads the IOS from flash into RAM upon boot.
6-ROM (read-only memory) Used to start and maintain the router. Holds the POST and the bootstrap program as well as the mini-IOS.
7-Flash memory Stores the Cisco IOS by default. It is EEPROM (electronically erasable programmable read-only memory) created by Intel.
8-NVRAM (nonvolatile RAM) Used to hold the permanent configuration of router. The configuration register is stored in NVRAM.
9-Configuration register It's a 16 digit hexadecimal configuration file that is used to control how the router boots up. Default value is set to 0x2102, which tells the router to load the IOS from flash memory as well as to load the configuration from NVRAM.
10- IOS Internet-networking Operating System. The kernel of Cisco Router IOS, developed by William Eager.
Now you know the different kinds of router components, you can move to learn Booting process of Router.
The Router Boot Sequence
Every device that uses operating system performs a series of steps, called the boot sequence, to test the hardware and load the necessary software. The router boot sequence consists of the following steps:
Step 1. The router performs a POST. The POST tests the hardware to verify that all components of the device are operational and present. The POST is stored in and run from ROM (read-only memory).
Step 2. The bootstrap then looks for and loads the Cisco IOS software. The bootstrap program is responsible for finding where each IOS program is located and then loading the file. By default, the IOS software is loaded from flash memory in all Cisco routers. The default order of an IOS loading from a router is flash, TFTP server, then ROM.
Step 3. The IOS software looks for a valid configuration file stored in NVRAM. This file is called startup-config.
Step 4. If a startup-config file is in NVRAM, the router will copy this file and place it in RAM and call the file running-config.
Step 5. Finally you will get router user console prompt. Where you can perform all the tasks.
To configure and troubleshoot a Cisco internetwork, you need to know the major components of Cisco routers and understand what each one does.
1-Bootstrap Stored in the ROM, It will boot the router and then load the IOS.
2-POST (power-on self-test) Stored in the ROM, the POST is used to check the basic functionality of the router hardware and determines which interfaces are present.
3-ROM monitor Stored in the ROM, the ROM monitor is used for manufacturing, testing, and troubleshooting.
4-Mini-IOS Called the RXBOOT or bootloader 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. Mini-IOS is not present on every router.
5-RAM (random access memory) Used to hold ARP cache, routing tables, software and data structures that allow the router to function. Running-config is stored in RAM, and most routers loads the IOS from flash into RAM upon boot.
6-ROM (read-only memory) Used to start and maintain the router. Holds the POST and the bootstrap program as well as the mini-IOS.
7-Flash memory Stores the Cisco IOS by default. It is EEPROM (electronically erasable programmable read-only memory) created by Intel.
8-NVRAM (nonvolatile RAM) Used to hold the permanent configuration of router. The configuration register is stored in NVRAM.
9-Configuration register It's a 16 digit hexadecimal configuration file that is used to control how the router boots up. Default value is set to 0x2102, which tells the router to load the IOS from flash memory as well as to load the configuration from NVRAM.
10- IOS Internet-networking Operating System. The kernel of Cisco Router IOS, developed by William Eager.
Now you know the different kinds of router components, you can move to learn Booting process of Router.
The Router Boot Sequence
Every device that uses operating system performs a series of steps, called the boot sequence, to test the hardware and load the necessary software. The router boot sequence consists of the following steps:
Step 1. The router performs a POST. The POST tests the hardware to verify that all components of the device are operational and present. The POST is stored in and run from ROM (read-only memory).
Step 2. The bootstrap then looks for and loads the Cisco IOS software. The bootstrap program is responsible for finding where each IOS program is located and then loading the file. By default, the IOS software is loaded from flash memory in all Cisco routers. The default order of an IOS loading from a router is flash, TFTP server, then ROM.
Step 3. The IOS software looks for a valid configuration file stored in NVRAM. This file is called startup-config.
Step 4. If a startup-config file is in NVRAM, the router will copy this file and place it in RAM and call the file running-config.
Step 5. Finally you will get router user console prompt. Where you can perform all the tasks.
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