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.

You can connect to a Cisco router to configure it, verify its configuration, and check statistics. There are different ways to do this, but most often, the first place you would connect to is the console port. The console port is usually an RJ-45 (8-pin modular) connection located at the back of the router–by default, there’s no password set.

You can also connect to a Cisco router through an auxiliary port–which is really the same thing as a console port, so it follows that you can use it as one. But this auxiliary port also allows you to configure modem commands so that a modem can be connected to the router. This is a cool feature—it lets you dial up a remote router and attach to the auxiliary port if the router is down and you need to configure it “out-of-band” (meaning “out-of-the-network”). “In-band” means the opposite—configuring the router through the network.

The third way to connect to a Cisco router is in-band, through the program Telnet. Telnet is a terminal emulation program that acts as though it’s a dumb terminal. You can use Telnet to connect to any active interface on a router, such as an Ethernet or serial port.

When you first bring up a Cisco router, it will run a power-on self-test (POST). If it passes, it will then look for and load the Cisco IOS from flash memory–if an IOS file is present. (Just in case you don’t know, flash memory is an electronically erasable programmable read-only memory– an EEPROM.) After that, the IOS loads and looks for a valid configuration–the startup-config– that’s stored by default in nonvolatile RAM, or NVRAM. The following messages appear when you first boot or reload a router:

System Bootstrap, Version 12.2(13)T, RELEASE SOFTWARE (fc1)
Copyright (c) 2000 by cisco Systems, Inc.
C2600 platform with 32768 Kbytes of main memory

This is the first part of the router boot process output. It’s information about the bootstrap program that first runs the POST, and then tells the router how to load, which by default is to find the IOS in flash memory.

The next part shows us that the IOS is being decompressed into RAM:

program load complete, entry point: 0×80008000, size:
0×43b7fc
Self decompressing the image :
###############################
###########################
################### [OK]

Before you upgrade or restore a Cisco IOS, you really should copy the existing file to a TFTP host as a backup just in case the new image crashes and burns.

And you can use any TFTP host to accomplish this. By default, the flash memory in a router is used to store the Cisco IOS. In this page describe how to check the amount of flash memory, how to copy the Cisco IOS from flash memory to a TFTP host, and how to copy the IOS from a TFTP host to flash memory.

But before you back up an IOS image to a network server on your intranet, you’ve got to do these three things:

1. Make sure you can access the network server.
2. Ensure that the network server has adequate space for the code image.
3. Verify the file naming and path requirement.

And if you have a laptop Ethernet port directly connected to a router’s Ethernet interface, as shown in Figure as below, you need to verify the following before attempting to copy the image to or from the router:

Backing Up the Cisco Router Configuration
To copy the router’s configuration from a router to a TFTP server, you can use either the copy running-config tftp or the copy startup-config tftp command. Either one will back up the router configuration that’s currently running in DRAM, or that’s stored in NVRAM.

Verifying the Current Configuration
To verify the configuration in DRAM, use the show running-config command (sh run for short) like this:

Router#sh run
Building configuration…
Current configuration:
!
version 12.0

The current configuration information indicates that the router is now running version 12.0 of the IOS.

Verifying the Stored Configuration
Next, you should check the configuration stored in NVRAM. To see this, use the show startup-config command (sh start for short) like this:

Router#sh start
Using 366 out of 32762 bytes
!
version 11.2

The second line shows you how much room your backup configuration is using. Here, we can see that NVRAM is 32KB and that only 366 bytes of it are used.