Booting Process Of a Cisco Router

Booting Process of a Cisco Router.

In this article I am going to show you, how the booting process of Cisco router will take place and which is very important to know for every technical persons which are in networking field. So let’s start... Booting process of a cisco router are as follows step by step.

1.       POST

·         The router performs a POST, The POST test the hardware to verify that all components of the devices are operational and present.

·         For example: The POST checks for the different interface on the router. The POST is stored in and run from ROM (Read Only Memory).

2.       ROM (0x2102, 0x2142)

·         The bootstrap then looks for and loads the cisco IOS software.

·         Bootstrap is a program in ROM that is used to execute programs. It is responsible for finding where each IOS program is located and then loading the file, by default, the IOS software is loaded from the flash memory in all cisco routers.

·         The default order of an IOS loading from a router in flash, TFTP, server then ROM.

3.       IOS

·         It is stands for Internetwork operating System.

·         The IOS looks for a valid configuration file stored in NVRAM. This file called startup-config and is only there if an administrator copies the running-config file into NVRAM.

4.       NVRAM

·         Non-volatile RAM holds router’s configuration files.

·         If a startup-config file is in NVRAM, the router will copy this file and place in it in RAM and call the file running-config.

·         The router will use this file to run this file to run this file to run the router. The router should now be operational. If a startup-config file is not in NVRAM, the router will broadcast out any interface that detects carrier detect (cd) for a TFTP host looking for a configuration, and when that fails, it will start the setup mode configuration process.

5.       RAM

·         Random-access Memory. Stores operational information such as routing tables and the running configuration file.

·         Its content are lost when the router is power down or reloaded.

·         By default, routers look here first for an internetwork operating system (IOS) file during boot.

  Some important points to remember

• RAM contents are lost on reload, where NVRAM and Flash contents are not.
•  NVRAM holds the startup configuration file, where RAM holds the running configuration file.
• 0x2102 is default. Router looks for a startup configuration file in NVRAM and for a valid IOS image in Flash.
• 0x2142 NVRAM contents are bypassed, startup configuration is ignored.
• 0x2100 router boots into ROM monitor mode.