[Cisco Networking Academy] Del Mar College
ITNW 1392-Beginning Router Configuration
 Instructor:Michael P. Harris
Sem2Les10

Semester 2, Lesson 10 Notes:

Sources for Cisco IOS Software

The default source for Cisco IOS software depends on the hardware platform, but most commonly the router looks to the 'configuration commands' saved in NVRAM.

You can specify other sources where the router should look for software, or the router will use its own "fall back sequence" as necessary to load software. Settings in the "configuration register" enable alternatives for where the router will bootstrap Cisco IOS software.

You can specify "enabled config-mode boot" (Router(config)# boot...) system commands to enter fall back sources for the router to use in sequence. Save these statments in NVRAM to use during the next startup with the command "copy running-config startup-config". The router will use these commands as needed, in sequence, when it restsarts.

However, if NVRAM lacks boot system commands the router can use; the system has its own 'fall back alternatives':
  1. the router will fall back and use defalut Cisco IOS in Flash memory.
  2. If Flash memory is empty, the router will try its next TFTP alternative. ...The router uses the configuration register value to form a filename from which to boot a default system image stored on a network.

2. What important command displays information about the Cisco IOS software that is currently running on the router, including the 'configuration register' setting?
"show version"

The order in which the router looks for system bootstrap information depends on the 'boot field' setting in the "configuration register". You can change the default "configuration register" setting with the 'enabled config-mode command', "config-register" (Router(config)# config-register 0x10F^Z).

The "configuration register" is a 16-bit register in NVRAM. The lowest four bits of the configuration register (bits 3, 2, 1, and 0) form the 'boot field'. Configuration register values (bits 3, 2, 1, and 0): 

 0x100 ROM monitor mode                boot field 0-0-0-0
 0x101 Boot from ROM                   boot field 0-0-0-1
 0x102 - 0x10F Examine NVRAM           boot field 0-0-1-0-1-1-1-1
To check the boot field setting, for example, to verify the config-register command, you must use the "show version" command. Note: You will not see evidence of any config-register setting in output from either the "show running-config" or "show startup-config comands".

The command "copy running-config startup-config" saves the command in NVRAM.

3. If both flash memory is corrupted and the network server fails to load the software image, what is the final software bootstrap option?
(3)Booting from ROM.

A 'TFTP server' can be another router, or it can be a host system. The TFTP host can be any system (Unix, DOS, Windows) with TFTP loaded and is able to contain files on the TCP/IP network. You will be copying software between the TFTP host and Flash memory in the router.

4. What comand would you use to make sure that you can see and write into Flash and verify that the router has sufficient room in Flash to accomodate the Cisco IOS software image you want to load?

"show flash"

  1. Command used to verify that you have sufficient memory on your system for the Cosci IOS software you want to load.
  2. Command used to learn the name of the system image file.

With Cisco IOS Release 11.2, the naming convention for Cisco IOS contains three parts:(Ex. igs-inr-1, c4500-aj-m, gs7-k-mz)

  1. The first part of the image name contains the platform on which the image runs. (ex. cpa25, igs, c4500, gs7)
  2. The second part of the image name identifies the special capabilities of the image. A letter or series of letters identifies the feature sets supported in the image. (Ex. 1, cg, inr, aj, k)
  3. The third part of the image name specifies where the image runs and if it has been 'zip' compressed. (Ex. 1, m, mz)

5. What two related commands are useful for transferring Cisco IOS images between tftp server and flash memory?

1. "copy tftp flash" - Copy the system image to a TFTP server.
Provides for a backup copy of the current Cisco IOS software image.
2. "copy tftp flash" - Download the new image from the TFTP server.
This command begins operation by requesting the 'IP address' of the remote host that will act as a TFTP server. Next you are prompted for the 'image name' of the update image. Following an opportunity to confirm your entries, the procedure asks if you are willing to 'erase Flash'. Each exclamation point (!) means that one User Datagram Protocol (UDP) segment has successfully transferred. The series of Vs indicates successful check run verification of a segment.

Use the "show flash" command to view the file and to compare its size with that of the original on the server before changing the 'boot system commands' to use the updated image. Following a successful copy, the "reload" command boots up the router as specified with the boot system system using the updated image.

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