1. Performing the POST
2. Loading the bootstrap program
3. Locating and loading the Cisco IOS software
4. Locating and loading the startup configuration file or entering setup mode
1. Performing the POST
The Power-On Self
1. Performing the POST
2. Loading the bootstrap program
3. Locating and loading the Cisco IOS software
4. Locating and loading the startup configuration file or entering setup mode
1. Performing the POST
The Power-On Self Test (POST) is a common process that occurs on almost every computer during bootup. The POST process is used to test the router hardware. When the router is powered on, software on the ROM chip conducts the POST. During this self-test, the router executes diagnostics from ROM on several hardware components including the CPU, RAM, and NVRAM. After the POST has been completed, the router executes the bootstrap program.
2. Loading the Bootstrap Program
After the POST, the bootstrap program is copied from ROM into RAM. Once in RAM, the CPU executes the instructions in the bootstrap program. The main task of the bootstrap program is to locate the Cisco IOS and load it into RAM.
Note: At this point, if you have a console connection to the router, you will begin to see output on the screen.
3. Locating and Loading Cisco IOS
Locating the Cisco IOS software. The IOS is typically stored in flash memory, but can also be stored in other places such as a TFTP (Trivial File Transfer Protocol) server.
If a full IOS image can not be located, a scaled-down version of the IOS is copied from ROM into RAM. This version of IOS is used to help diagnose any problems and can be used to load a complete version of the IOS into RAM.
Note: A TFTP server is usually used as a backup server for IOS but it can also be used as a central point for storing and loading the IOS. IOS management and using the TFTP server is discussed in a later course.
Loading the IOS. Some of the older Cisco routers ran the IOS directly from flash, but current models copy the IOS into RAM for execution by the CPU.
Note: Once the IOS begins to load, you may see a string of pounds signs (#), as shown in the figure, while the image decompresses.
4. Locating and Loading the Configuration File
Locating the Startup Configuration File. After the IOS is loaded, the bootstrap program searches for the startup configuration file, known as startup-config, in NVRAM. This file has the previously saved configuration commands and parameters including:
any other configurations saved by the network administrator
If the startup configuration file, startup-config, is located in NVRAM, it is copied into RAM as the running configuration file, running-config.
Note: If the startup configuration file does not exist in NVRAM, the router may search for a TFTP server. If the router detects that it has an active link to another configured router, it sends a broadcast searching for a configuration file across the active link. This condition will cause the router to pause, but you will eventually see a console message like the following one:
%Error opening tftp://255.255.255.255/network-confg (Timed out)
%Error opening tftp://255.255.255.255/cisconet.cfg (Timed out)
Executing the Configuration File. If a startup configuration file is found in NVRAM, the IOS loads it into RAM as the running-config and executes the commands in the file, one line at a time. The running-config file contains interface addresses, starts routing processes, configures router passwords and defines other characteristics of the router.
Enter Setup Mode (Optional). If the startup configuration file can not be located, the router prompts the user to enter setup mode. Setup mode is a series of questions prompting the user for basic configuration information. Setup mode is not intended to be used to enter complex router configurations, and it is not commonly used by network administrators.
When booting a router that does not contain a startup configuration file, you will see the following question after the IOS has been loaded:
Would you like to enter the initial configuration dialog? [yes/no]: no
Setup mode will not be used in this course to configure the router. When prompted to enter setup mode, always answer no. If you answer yes and enter setup mode, you can press Ctrl-C at any time to terminate the setup process.
When setup mode is not used, the IOS creates a default running-config. The default running-config is a basic configuration file that includes the router interfaces, management interfaces, and certain default information. The default running-config does not contain any interface addresses, routing information, passwords, or other specific configuration information.
Command Line Interface
Depending on the platform and IOS, the router may ask the following question before displaying the prompt:
Would you like to terminate autoinstall? [yes]:
Press the Enter key to accept the default answer.
Note: If a startup configuration file was found, the running-config may contain a hostname and the prompt will display the hostname of the router.
Once the prompt displays, the router is now running the IOS with the current running configuration file. The network administrator can now begin using IOS commands on this router.
Note: The bootup process is discussed in more detail in a later course.
Verifying Router Bootup Process
The show version command can be used to help verify and troubleshoot some of the basic hardware and software components of the router. The show version command displays information about the version of the Cisco IOS software currently running on the router, the version of the bootstrap program, and information about the hardware configuration, including the amount of system memory.
The output from the show version command includes:
Cisco 