Transcript Configuration Register

CCNA 2 v3.1 Module 5
Managing Cisco IOS Software
© 2004, Cisco Systems, Inc. All rights reserved.
1
Objectives
Router Startup Sequence
Router Startup Sequence
•
The purpose of the router power-on/bootup sequence is to not only verify the operation of
hardware but also load the correct IOS and configuration file.
•
The router follow a predefined set of steps when booting, listed below:
When the router is first powered-on, it executes the Power-on self test or POST
These diagnostics are located in ROM and verify the proper operation of the router’s
hardware
If the router passes the POST, the bootstrap loader in ROM executes
The bootstrap loader provides capability to load the IOS
Now the router is ready to load the operating system, Cisco’s IOS
The IOS can be found in several different places, flash, TFTP, or ROM. The boot field of the
configuration register will indicate the location of the IOS image
After the operating system is loaded and operational, the configuration file from NVRAM is then
loaded and executed
If you erase the configuration from NVRAM you can observe the process of first checking
for a TFTP server and then entering a question driven setup menu when the TFTP server
is not found
Use Control <C> to exit the setup menu
Stages of the Router Power-on Boot Sequence
Test the router hardware
POST
Run program which provides
the ability to read from
FLASH
Bootstrap
Flash
TFTP
ROM
Cisco
Internetwork
Operating
System
NVRAM
TFTP
Find and load the Cisco IOS
software into RAM
Console
Configuration
File
Find and apply configuration
statements
i.e. interface addresses, routing
protocol configuration
Locating and Loading the Cisco IOS
• The router can load the Cisco IOS from several different
locations that can be specified by the operator
• 1. Through the use of the boot system commands, the
router will look for the location of the IOS.
These boot system commands will be executed only if they are
saved in NVRAM
• 2. If no boot system commands are saved in NVRAM, the
router will use the default fallback process: flash, TFTP,
and finally ROM
The IOS loaded from ROM is only a subset of the IOS loaded
from flash
Locating IOS Software
Using the boot system Command
• Once the boot system command has been saved to the
start-up configuration in NVRAM, it will be used in the next
startup to locate the IOS
• Loading the IOS from flash memory has the
advantage of being located locally
• Loading the IOS from a TFTP server might be an
option if flash memory has been corrupted
• Finally, if the IOS is not loaded from flash or the TFTP
server, a subset of the IOS can be loaded from ROM
How a Cisco Device Locates and Loads IOS
The router uses boot system commands saved in NVRAM to locate the IOS.
Router#configure terminal
Router(config)# Boot system flash c4500-p-mz_111-18.bin
Router(config)# Boot system tftp c4500-1.bin 192.168.1.7
Router(config)# Boot system rom
Router(config)# exit
Router(config)# copy running-config startup-config
After it is reloaded, the router will try these commands in the order they were
entered.
The order in which the router looks for system bootstrap information depends
on the boot field setting in the configuration register. The default
configuration register setting can be changed with the following command:
Router(config)#config-register 0x2142
Note hex number
Configuration Register – Boot Field
To view the current values of the configuration register:
Router# show version
..<output omitted>..
Configuration register is 0x2102
The configuration register is a 16-bit register in NVRAM.
Note: the notation 0x informs us that the following number is a hexadecimal number.
From the example, Hex 2142 is 0010.0001.0000.0010 in binary.
The lowest four bits of the configuration register form the boot field.
Configuration register is 0x2102
Setting
0xnnn0
0xnnn1
0xnnn2
Description
Enter ROM monitor mode
on reload.
Boot automatically from ROM.
Use boot system commands in NVRAM, this is the default.
The Configuration Register
•
•
16-bit value
bits divided into fields
•
0 – 3 = boot field
– 0 = bootstrap prompt,
– 1 = load IOS from ROM
– 2 = check for boot system
commands or load IOS from
Flash
•
6 = ignore NVRM contents
•
8 = break key disabled
•
11 – 12 = console line speeds
•
13 = boot from network
indefinitely
Troubleshooting IOS Boot Failure
•
In the event that the router does not
boot properly, there are several
things that could be wrong:
Configuration file has missing or
incorrect boot system statement
Incorrect configuration register value
Corrupted flash image
Hardware failure
•
To identify the boot image source,
type the show version command
and look for the line that identifies
the image boot source
•
Use the show running-config
command and look for a boot
system statement near the top of the
configuration. If the boot system
statement points to an incorrect IOS
image, delete the statement using
the “no” version of the command
IOS File System Overview
1. The two types of software required are _________________
operating system and
_____________.
configuration
2. The ___________
Cisco IOS® is software that allows the hardware to function as a
router or switch.
3. The configuration contains the “instructions” that define how the device is
to _________________.
route or switch
4. A ____________________
network administrator creates the configuration that defines the
desired functionality of the Cisco device.
5. The IOS is stored in a memory area called _______.
flash
6. The flash allows the IOS to be _________
upgraded or stores _____________
multiple IOS files.
7. The IOS is copied into and run from ______.
RAM
8. A copy of the configuration file is stored in ________.
NVRAM
9. This is referred to as the “______________”.
startup-config
10. The startup configuration is copied into RAM at _________.
boot time
11. This configuration in RAM is the configuration used to _______
operate the router.
12. It is referred to as the “_____________”.
running-config
13. Beginning with version 12, the ______________________
Cisco IOS File System provides a
single method to perform all file system management.
14. The IFS uses ______
URLs to specify files on network devices and the network.
Identifying Boot Image Source
Software Components in Memory
Fields in the IOS Name
IOS Naming Convention
Platform Feature Set
Binary file
System image file is "flash:c2600-d-mz.122-16a.bin"
Located in Flash
File Format
IOS Version number
Examples of feature-set categories are:
• Basic
• Plus
• Encryption (designated by ‘k8’ or ‘k9’ in IOS 12.2 and later)
The file format flag “z” specifies if the IOS is compressed in flash and if
the IOS is relocatable.
A relocatable image is copied from flash into RAM to run.
A non-relocatable image is run directly from flash.
As Cisco develops newer versions of the IOS, the numerical version
number increases.
File System
•
Any location that information is stored can be examined or addressed
using the standard directory structure format
Managing Configuration Files using TFTP
To store the current configuration on a network TFTP server use the
following command:
My# copy running-config tftp
Remote host []? 131.108.2.155
Name of configuration file to write[my-config]? myconfig
Write file myconfig to 131.108.2.155 ? [confirm] y
!!!!!!!!!!!!!!!!!!!! [OK]
Writing myconfig
A configuration file on a network servers can be used to configure a router:
Router# copy tftp running-config
Host or network configuration file [host]?
IP address of remote host[255.255.255.255]? 10.0.0.13
Name of configuration file [Router-config] ? myconfig
Configure using myconfig from 10.0.0.13? [confirm] y
Booting myconfig from 10.0.0.13:
!!!!!! [OK-180/16000 bytes]
Managing Configuration Files Using TFTP
Managing Configuration Files Using Copy and
Paste
Managing Configuration Files using Capture and Send
To capture the configuration from HyperTerminal to a text file:
1.
Select Transfer  Capture Text
2.
Specify a name for the text file to capture the output to
3.
Select Start to start capturing text
Now all that appears on the screen will be written to the text file.
4.
Display the configuration with a show running-config
Press the space bar when –more– is displayed
5.
To stop the capture select Transfer  Capture Text  Stop
After the capture is complete, the configuration file needs to be edited to remove extra text, to add
commands or to add comments with a !
HyperTerminal can be used to restore a configuration. The edited backup of the configuration can be
copied into the router:
1.
Enter router global configuration mode.
2.
From HyperTerminal, click on Transfer > Send Text File.
3.
Select the name of the saved configuration file.
4.
The lines of the file will be entered into the router as if they were being typed at the CLI. Observe
any errors.
Lost / Damaged IOS
•
If the router will not properly boot, a new IOS image needs to be
downloaded
•
The IOS file may be recovered using one of two methods:
1.
Use Xmodem to restore the image through the console
2.
Download the image using TFTP from the ROMmon mode
Managing IOS Images Using TFTP
Managing IOS Images using TFTP
Occasionally the router will need to have the IOS upgraded or restored.
Also the IOS on a new router should be backed up.
Nescot01# copy tftp flash
Address or name of remote host []? 192.168.1.17
Source filename []? c2600-d-mz.122-16a.bin
Destination filename [c2600-d-mz.122-16a.bin]?
Accessing tftp://192.168.1.17/c2600-d-mz.122-16a.bin
Erase Flash: before copying? [confirm]
Erasing the flash file system will remove all files
Continue? [confirm]
Erasing device eeeeeeeeeeeeeeeeeeee.. Erased
Loading c2600-d-mz.122-16a.bin from 192.168.1.17 (via
FastEthernet 0/0): !!!!!!!!!!!!!!!!!!!!!!
Verifying checksum .. .. .. ..OK
[OK 8906598 bytes]
8906598 bytes copied in 270.12 secs
Recovering IOS Images
To identify why the IOS image did not load from flash
1. Check to see if an image is available in flash:
rommon 1> dir flash:
2. If a valid image is present try to boot it:
rommon 1> boot flash:c2600-is-mz.121-5
3. If router now boots properly check the configuration register:
Router# show version
4. If the configuration register value is correct check for boot system
commands:
Router# show startup-config
If the router will not properly boot from the image or there is no IOS image,
a new IOS will need to be downloaded.
The IOS file may be recovered using either:

Xmodem to restore the image through the console

TFTP from the rommon mode
Managing IOS Using XModem
Download using Xmodem from rommon >
To restore the IOS through the console you need:
1.
Copy of the IOS file on a PC.
2.
Terminal emulation program such as HyperTerminal.
Changing the baud rate from 9600 bps to 115200 bps speeds up the
download. To change console speed from rommon:
rommon 1> confreg
Configuration Summary
..<output omitted>..
Console baud: 9600
Boot: the ROM Monitor
Do you wish to change the configuration? y/n [n]: y
Enable diagnostic mode y/n [n]:
..<output omitted>..
Change console baud rate? y/n [n]: y
Enter rate: 0 = 9600, 1 = 4800, 2 = 1200, 3 = 2400 4
= 19200, 5 = 38400, 6 = 57600, 7 = 115200 [0]: 7
Note:
After changing the console speed and restarting the router in rommon
mode, the original terminal session at 9600 bps should be terminated
and a new session started to match the 115200 bps console speed.
The confreg Command
Download using Xmodem from rommon >
The xmodem command can be used from the rommon mode to restore the IOS
software image from the PC:
Use CRC for error checking during the download
Rommon 1> xmodem -c c2600-is-mz.122-10a.bin
Do not start sending program yet…
Warning: All existing data in bootflash will be lost!
Invoke this application only for disaster recovery.
Do you wish to continue? y/n [n]: y
Ready to receive file c2600-is-mz.122-10a.bin . . .
Next, In HyperTerminal select Transfer > Send File.
1.
2.
3.
Specify the image name/location
select Xmodem as the protocol
start the transfer.
During the transfer the Sending File popup will display the status of the transfer.
On completion, return config-register and HyperTerminal settings to normal.
TFTP and Environment Variables
Downloading the image using TFTP from rommon is the fastest way to
restore an IOS image to the router. This is done by setting environmental
variables and then using the tftpdnld command:
rommon 1> ip_address=10.0.0.1
rommon 2> ip_subnet_mask=255.255.255.0
rommon 3> default_gateway=10.0.0.254
rommon 4> tftp_server=192.168.1.1
rommon 5> tftp_file=GAD/basic0204/c2600-I-mz.12-1.bin
rommon 6> set
IP_ADDRESS=10.0.0.1
IP_SUBNET_MASK=255.255.255.0
DEFAULT_GATEWAY=10.0.0.254
TFTP_SERVER=192.168.1.1
TFTP_FILE=GAD/basic0204/c2600-i-mz.12-1.bin
rommon 7> tftpdnld
..<output omitted>..
Receiving GAD/basic0204/c2600-I-mz.12-1.bin from
192.168.1.1 !!!!!!!!!!!!!!!!!! File reception completed
The set Command
The tftpdnld Command
File System Verification
• There are several commands used to verify the router
file system:
One is the show version command. This command is used
to check the current image and available flash. It also
verifies the source of the IOS image and the config
register boot field setting
The show flash command is also used to verify the flash
system. This command identifies the amount of flash
that is available. It also confirms that there is ample
space to store a new IOS image
The show version Command
The show flash Command
Summary