Cisco Router Boot Process and Sequence

Cisco Router Boot Process and Sequence

Both Cisco switches and routers follow a same Cisco Router Boot Process and Sequence to load the IOS image and boot configuration file into RAM. In this article we will discus the process of Cisco Router startup. Whenever a Cisco devices started it goes into following step for loading Cisco IOS.

1. The IOS image file, stored in flash memory, contains the IOS.
2. Flash memory also stores other system files.
3. The NVRAM stores configuration parameters.

The running configuration is modified when the network administrator performs device configurations. The changes that have been made in the running-config file must be saved in the configuration file in the NVRAM, in case the router is rebooted or is not receiving power.

ROUTER BOOT PROCESS

There are three phases of great importance in the boot process:

What is post in Cisco router?

During the self-test on power-up (POST), the router performs diagnostics in the ROM on various hardware components, including the CPU, RAM and NVRAM. After POST, the boot program is copied from ROM to RAM. The main task of the boot program is to locate the Cisco IOS and load it into RAM.

Ref: 9tut.com

In general, the IOS is stored in flash memory and copied to RAM for the CPU to run. If the IOS image is not in flash memory, the router can search for it with a trivial file transfer protocol (TFTP) server. If a complete IOS image cannot be located, a limited IOS is copied to RAM, which It can be used to diagnose problems and transfer a full IOS to flash memory.

The boot configuration file is located and loaded or the configuration mode is entered : The boot program copies the NVRAM startup configuration file to RAM. This becomes the running configuration. If the startup configuration file does not exist in NVRAM, the router can be configured to search for a TFTP server. If no TFTP server is found, the router displays the request to enter the configuration mode.