For many beginners, the ROM Monitor of Cisco routers is often unfamiliar or even daunting. The reason is very simple. First, we do not often use this mode and are not familiar with its related operations; second, Operation errors in ROM Monitor mode often cause fatal damage To routers, such as destroying IOS files in flash, resulting in system crashes. So many people put their hands on it and are discouraged.
In fact, ROM Monitor is not complex. It is only a low-level operating system of a Cisco router. It is usually used for testing and troubleshooting. It can be done easily with little time. The following describes how to use ROM Monitor, which is the two most common problems for network administrators in actual work.
Scenario 1: vro password recovery
To prevent others from knowing the vro password, especially the privileged password, and threatening local network security, many administrators have made the password particularly complex. However, after configuring the vro, we seldom operate on the vro. After a while, when we need to configure the vro, the password may be lost.
At this time, we only need a PC operating system for the Windows series), a Console cable and the corresponding interface converter, and then follow the steps below to easily deal with it.
1) setting up a super terminal for a PC enables us to use the Console port of the vro to directly operate the vro because the process is very simple. I will omit it to save space ).
2) Start the vro and press the "Break" or "Ctrl + Break" key in the first 60 seconds to enter the ROM Monitor mode of the vro.
3) Next we will give a brief description of the Cisco 2600 series routers most commonly used by beginners.
Press Ctrl + Break to enter ROM Monitor mode)
rommon 2 > confreg 0x2142 |
Use this command to modify the value of the configuration register of the vro so that the vro does not load the startup configuration when it is restarted next time, so as to skip user password and privileged password verification and enter the privileged mode.
You must reset or power cycle for new config to take effect
rommon 3 > reset |
Run the following command to restart the vro:
Would you like to enter the initial configuration dialog? [yes/no]: n |
Select no to enter the CLI mode.
Press RETURN to get started! |
Press enter to continue the next step.
Router>en
Router#show version |
Use the show version command to check that the configuration register value is 0x2142.
Use this command to load the startup configuration and set a new password. If this step is not performed, the new password setting will fail after the next restart.
Router#conf t
Router(config)#config-register 0x2102 |
The next restart of the vro will load the startup configuration. The new password must be used for verification.
Router(config)#end
Router#copy run star |
Save the running configuration to the startup configuration.
Destination filename [startup-config]?
Building configuration...
[OK] |
Password Recovery for Cisco 2500, 2000, 3000, 4000, and 7000 Series routers is basically the same as the above operations. The main difference is that the command to modify the configuration register is "o/r 0x2142 ", and the restart command is "I". The vrouters of other series are basically the same as those of the 2600 series.
Scenario 2: upgrade or repair of IOS files in Router flash
In comparison, the second situation is more rare, but also more serious. It often occurs when the router system crashes due to errors in the upgrade of the IOS version or other hardware and software faults, the entire network is paralyzed.
At this time, we often need to repair the router in ROM Monitor mode.
The following is an example of a student's problem. The student experienced the following faults when upgrading the IOS of a Cisco 2600 router:
System Bootstrap, Version 11.3(2)XA4, RELEASE SOFTWARE (fc1)
Copyright (c) 1999 by Cisco Systems, Inc.
TAC:Home:SW:IOS:Specials for info
C2600 platform with 32768 Kbytes of main memory
loadprog: bad file magic number: 0x0
boot: cannot load "flash:" |
Then, the router boot program repeats the above process. After the failure, it enters the ROM Monitor mode.
This command causes the router to reload the IOS file in flash.
boot: cannot determine first file name on device "flash:" |
After determining that the fault is caused by the failure of the router, we need to restore the IOS file from the TFTP Server to the flash file of the router. In this case, we can perform this task in two ways: first, use the PC with the Cisco TFTP Server installed to recover the IOS router over Ethernet, and second, in ROM Monitor mode, use the xmodem command to restore the IOS router by using a transport protocol that transfers files using the Console cable.
Here, we give priority to the first method. The steps are as follows.
1) connect the PC installed with the Cisco TFTP Server to the Ethernet interface of the router through Ethernet and run the Cisco TFTP Server program.
2) log on to the Console using a Super Terminal. The Console vro has been started and logged on when a fault is found. The terminal screen is shown as follows:
This command displays the default vro settings:
PS1=rommon ! >
IP_ADDRESS=192.168.1.1
IP_SUBNET_MASK=255.255.255.0
DEFAULT_GATEWAY=192.168.1.2
TFTP_SERVER=192.168.1.2
TFTP_TIMEOUT=20000
TFTP_RETRY_COUNT=10
TFTP_FILE=/c2600-ik8o3s-mz.122-11.T/
?=1 |
3) Check the default vro settings and change the IP address of the PC to 192.168.1.2. We can also use the command TFTP_SERVER = 192.168.1.x to modify the settings, make sure that the IP address of the router, the default gateway, and the IP address of the PC are in the same CIDR block.
4) Specify the IOS file name to be restored and ensure that the file is in the root directory of the Cisco TFTP Server.
Rommon 3 > TFTP_FILE=/c2600-i-mz.121-3.T.bin |
Do not forget to add the extension file name. bin.
5) start to restore the IOS file:
Run this command to download the IOS file from the TFTF Server to flash. This command is only applicable to Cisco 2600 series routers.
IP_ADDRESS: 192.168.1.1
IP_SUBNET_MASK: 255.255.255.0
DEFAULT_GATEWAY: 192.168.1.2
TFTP_SERVER: 192.168.1.2
TFTP_FILE:/c2600-i-mz.121-3.T.bin
Invoke this command for disaster recovery only.
WARNING: all existing data in all partitions on flash will be lost!
Do you wish to continue? Y/n: [n]: y
Refreshing ing/c2600-i-mz.121-3.T.bin from 192.168.1.2
After confirmation, the router starts to download the IOS file, omitting multiple lines)
File completion tion completed.
Copying file/c2600-i-mz.121-3.T.bin to flash.
Erasing flash at 0x60fc0000
Program flash location 0x60160000 |
6) restart the router and run the new IOS.
The following is a normal startup process, so it is omitted)
There are many other commands with different functions in the Cisco ROM Monitor mode. We can use them to perform a series of tests and troubleshooting on the vro, for more information about this mode, visit the Cisco site www.Cisco.com to perform a search. the search keyword is Using the ROM Monitor.
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