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Router Boot Sequence – GeeksforGeeks

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A Router is a networking gadget that forwards knowledge packets between laptop networks. Router Boot sequence entails the next reminiscence parts:

  • Learn-Solely Reminiscence (ROM): ROM shops the bootstrap startup program of the router together with the working system software program and different check packages like POST packages (Energy On Self Check).
  • Flash Reminiscence: Flash reminiscence usually referred to as flash holds the IOS photos. The flash content material is utilized by the router on the time of reload. Flash is erasable and reprogrammable ROM.
  • Random Entry Reminiscence (RAM): RAM shops data equivalent to routing tables and working configuration recordsdata. RAM is risky therefore, its content material is misplaced throughout router energy down and reload.
  • Non-volatile RAM (NVRAM): NVRAM shops the startup configuration recordsdata. It’s non-volatile RAM; therefore contents should not misplaced throughout router energy down and reload.


Cisco routers have two varieties of ports: Interfaces and features. Interfaces join routers to different gadgets. Knowledge travels via these ports within the community. Interfaces are recognized by their title and quantity. Some frequent interfaces are:

We are able to configure routers by connecting them with different varieties of ports referred to as traces. Like interfaces, traces are additionally recognized by line title and quantity. Some frequent traces are:

  • Console Ports
  • Auxiliary Ports
  • VTY Ports

Command Line Interface:

IOS offers a command line interface to work together with the Cisco router. The command line interface is first used to configure and handle Cisco gadgets. It may be accessed via modem, console, and telnet connection. In CLI, we are able to sort a command and execute it.

Router Boot Sequence: 

The sequence of steps carried out by the router throughout the booting course of is named the router boot sequence. The router boot sequence defines the sequence during which the booting course of takes place in a router.

Steps of Router Boot Sequence:

  1. When the router is turned on it performs the POST (Energy On Self Check) program. The POST program assessments the current {hardware} and checks it’s operational or not. The POST packages are saved and run from the ROM.
  2. The bootstrap program current within the ROM checks the Configuration Register worth to seek out the place to load the IOS. The default worth of configuration register 0x2102 signifies that the router ought to load the Cisco IOS Working System software program picture from the flash reminiscence and cargo the startup configuration.
  3. The Bootstrap Program seems to be for and hundreds the IOS program to the configuration register. This program can be answerable for initializing the {hardware} and discovering the IOS program location and loading the IOS picture from the flash reminiscence.
  4. If the Bootstrap program doesn’t discover the IOS picture it should act as ROM Monitor. It helps a command line that’s used to carry out configuration duties.
  5. The IOS finds the legitimate configuration file saved in NVRAM. This file is named startup-config.
  6. If the Startup configuration(startup-config) is current in NVRAM the router hundreds the file into RAM and applies the startup-config file. If the file shouldn’t be current in NVRAM it tries to load a file from TFTP. If no TFTP server responds it enters the Setup mode.
  7. When the Startup Configuration is loaded IOS will show CLI mode in consumer mode. 
Boot Sequence


Router Booting Course of Instance:

The router goes via the above steps throughout the booting course of.

  • The router is powered on.
  • POST is carried out which checks the {hardware} parts together with reminiscence and interfaces.
  • The bootstrap program is loaded and executed.
  • Bootstrap reads the configuration register worth which identifies how the router will boot up.
  • Relying on the worth of the configuration register, the bootstrap program finds and locates the IOS picture.
  • If bootstrap fails to load the IOS it should drop the boot sequence to ROMMON (ROM Monitor) mode for troubleshooting.
  • If IOS is loaded it finds and hundreds the configuration.
  • If the configuration shouldn’t be current, the system configuration dialog could be launched.
  • If the configuration is loaded, you’ll be introduced within the CLI interface.


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