Router Boot Sequence – GeeksforGeeks

A Router is a networking system that forwards information packets between laptop networks. Router Boot sequence entails the next reminiscence components:

• 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 pictures. 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 comparable to routing tables and working configuration information. RAM is unstable therefore, its content material is misplaced throughout router energy down and reload.
• Non-volatile RAM (NVRAM): NVRAM shops the startup configuration information. It’s non-volatile RAM; therefore contents will not be misplaced throughout router energy down and reload.

Ports:

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

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

• Console Ports
• Auxiliary Ports
• VTY Ports

Command Line Interface:

IOS gives a command line interface to work together with the Cisco router. The command line interface is first used to configure and handle Cisco units. It may be accessed by modem, console, and telnet connection. In CLI, we will kind a command and execute it.

Router Boot Sequence: 

The sequence of steps carried out by the router through the booting course of is named the router boot sequence. The router boot sequence defines the sequence by 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 exams 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 search 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 appears to be like for and masses the IOS program to the configuration register. This program can also be liable 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 masses the file into RAM and applies the startup-config file. If the file will not 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 person mode. 

 

Router Booting Course of Instance:

The router goes by the above steps through 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 masses the configuration.
• If the configuration will not be current, the system configuration dialog can be launched.
• If the configuration is loaded, you’ll be introduced within the CLI interface.