Router and Switch Boot Process

telecomops101

I just want to be sure that I understand this. When a router or switch boot's up, is the process the same for both as below:

POST
Bootstrap from ROM
Config-Register is looked at to determaine boot process
0=RomMon
1=RxBoot
2=normal boot process (flash, tftp)
If no Config -Register is found, follow Boot System command order


Also, where is the Config-Register stored: is it in NVRAM?
Where are the Boot System commands stored: is it also in NVRAM

iproute

telecomops101 wrote:

Also, where is the Config-Register stored: is it in NVRAM?
Where are the Boot System commands stored: is it also in NVRAM

That's a good question. I guess I just always assumed it was NVRAM.

Rearden

Am I the only one that is bothered that it is called the config REGISTER? Registers belong on CPUs if you ask me.

Paul Boz

Rearden wrote:

Am I the only one that is bothered that it is called the config REGISTER? Registers belong on CPUs if you ask me.

A register is just a memory location that can be accessed very quickly, which is what the configuration register does from nvram.

markzab

From the 57 page word doc I just completed (phase 2 of my study process)

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When a router boots up, it performs a series of steps, called the boot sequence, to test the hardware and load the necessary software. The boot sequence consists of the following steps:

1. The router performs a POST. The POST tests the hardware to verify that all components of the device are operational and present. For example, the POST checks for the different interfaces on the router. The POST is stored in and run from ROM (read-only memory).

2. The bootstrap looks for and loads the Cisco IOS software. The bootstrap is a program in ROM that is used to execute programs. 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.

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

4. If a startup-config file is in NVRAM, the router will load and run this file. The router is now operational. If a startup-config file is not in NVRAM, the router will start the setup-mode configuration upon bootup.

All Cisco routers have a 16-bit software register that’s written into NVRAM. By default, the configuration register is set to load the Cisco IOS from flash memory and to look for and load the startup-config file from NVRAM.