Cisco IOS XR ROM Monitor Guide, Release 3.8
ROM Monitor Overview and Basic Procedures
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Table Of Contents
ROM Monitor Overview and Basic Procedures
The ROM Monitor is a bootstrap program that initializes the hardware and boots the Cisco IOS XR  oftware when you power on or reload a router. A version of the ROM Monitor software exists on each card. If the Cisco IOS XR  oftware ca ot boot on a card, the card startup ends in ROM Monitor mode. When you co ect a terminal to a card that is in ROM Monitor mode, the ROM Monitor command-line interface (CLI) prompt is di layed:
Cisco CRS-1 Prompt
rommon B1
Cisco XR 12000 Serie #160;Router Prompt
rommon1
During normal operation, users do not see the ROM Monitor prompt or use ROM Monitor mode. ROM Monitor mode is used only in ecial circumstances, such as rei talling the entire software set, resetting the router pa word, or ecifying a configuration file to use at startup.
This chapter provides an overview of ROM Monitor concepts and operatio . For i tructio on how to perform various tasks in ROM Monitor mode, see the other chapters in this book.
This chapter includes the following main topics:
•
•
•
•
•
•
•
•
ROM Monitor Overview
The ROM Monitor software is known by many names. It is sometimes called ROMMON because of the CLI prompt in ROM Monitor mode. The ROM Monitor software is also called the boot software, boot image, or boot helper. On Cisco XR 12000 Serie #160;Routers, the Boothelper software is different from the ROM Monitor software, and it is described in
Although it is distributed with routers that use the Cisco IOS XR  oftware, ROM Monitor is a separate program from the Cisco IOS XR  oftware. During normal startup, the ROM Monitor initializes the cards, and then control pa es to the Cisco IOS XR  oftware. After the Cisco IOS XR  oftware takes over, ROM Monitor is no longer in use.
A copy of the ROM Monitor software exists on each card. If a card fails to boot the Cisco IOS XR  oftware, the ROM Monitor software takes control and places the card in ROM Monitor mode. Because a card in ROM Monitor mode is not ru ing the Cisco IOS XR  oftware, that card will be unavailable for normal router operatio .
When the Designated Secure Domain Router Shelf Controller (DSDRSC) in an SDR is placed in ROM Monitor mode, the router operatio are tra ferred to the standby DSDRSC (if available). If both the primary and standby DSDRSCs are in ROM Monitor mode, then the router operatio cease since the Cisco IOS XR  oftware is no longer ru ing.
Understanding the Role of the DSC
The active RP for the
owner SDR
is called the Designated Shelf Controller, or DSC. This card performs system-wide functio , including the creation of additional
non-owner
SDRs. If the DSC is placed in ROM Monitor mode, it is no longer ru ing the Cisco IOS XR  oftware. If a standby DSC is available, then the standby a umes router operatio . If a standby DSC is not available or is also placed in ROM Monitor mode, then router operatio will stop.
Designated Secure Domain Router Shelf Controller (DSDRSC)
In addition to the DSC, each SDR in the system contai at least one DSDRSC. The DSDRSCs provide configuration and administrative functio for a single SDR only. The DSC also serves as the DSDRSC for the owner SDR.
Acce ing ROMMON on the DSC
In most situatio , you will interact with ROM Monitor mode only on the DSC (DSDRSC for the owner SDR). The DSC contai the admin configuration for the entire system and distributes the required software to all the other nodes in the router. All the tasks in this document describe ROM Monitor mode acce ed through the DSC for the system.
The only time you will interact with a non-DSC node is when rei talling the Cisco IOS XR  oftware on the standby PRP of a Cisco XR 12000 Serie #160;Router. See
for more information.
Remember, the DSC is also the following:
•
The active RP of rack 0.
•
The DSDRSC for the owner SDR.
Environmental Variables and the Configuration Register
Two primary co ectio exist between ROM Monitor and the Cisco IOS XR  oftware: the ROM Monitor environment variables and the configuration register. The ROM Monitor environment variables define the location of the Cisco IOS XR  oftware and how to load it. After ROM Monitor has initialized the card, it uses the environment variables to locate and load the Cisco IOS XR  oftware.
The configuration register is a software setting that controls how a card starts up. One of the primary uses of the configuration register is to control whether the card starts in ROM Monitor mode or EXEC mode. The configuration register is set in either ROM Monitor mode or EXEC mode as needed. Typically, you set the configuration register using the Cisco IOS XR  oftware prompt on the active RP when you need to use ROM Monitor mode. When your maintenance in ROM Monitor mode is complete, you change the configuration register so the card will reboot with the Cisco IOS XR  oftware.
Acce ing ROM Monitor Mode with a Terminal Co ection
When an RP is in ROM Monitor mode, you can acce the ROM Monitor software only from a terminal co ected directly to the Co ole port of the card. Because the Cisco IOS XR  oftware (EXEC mode) is not operating, the nonmanagement interfaces (such as POS interfaces) are not acce ible. Basically, all Cisco IOS XR  oftware resources are unavailable. The hardware is there, but no configuration exists to make use of the hardware.
Network Management Acce and ROM Monitor Mode
Some people get confused when they start to use ROM Monitor mode. It is important to remember that ROM Monitor mode is a router mode, not a mode within the Cisco IOS XR  oftware. It is best to remember that ROM Monitor software and the Cisco IOS XR  oftware are two separate programs that run on the same router. At any given time, the router is ru ing one of these programs, but it never ru both at the same time.
One area that confuses people when using ROM Monitor and the Cisco IOS XR  oftware is that area that defines the IP configuration for the Management Ethernet interface. Most router users get comfortable with configuring the Management Ethernet interface in the Cisco IOS XR  oftware. When the router is in ROM Monitor mode, however, the router is not ru ing the Cisco IOS XR  oftware, so that Management Ethernet interface configuration is not available.
When you want to acce other devices, such as a TFTP server, while in ROM Monitor mode on Cisco CRS-1s, you must configure the ROM Monitor variables with IP acce information. On Cisco XR 12000 Serie #160;Routers, you must configure the Boothelper software, as described in
Entering ROM Monitor Mode
The following sectio describe two ways to enter ROM Monitor mode:
•
•
Resetting the Configuration Register and Reloading a DSC to ROM Monitor Mode
In normal operating conditio , it should not be nece ary to use ROM Monitor mode. If you do find it nece ary to place a designated shelf controller (DSC) in ROMMON, make sure that the system is in a steady state and that you are prepared for the co equences of a system reload. In particular, verify the items described in the
Prerequisites
Before you place a DSC in ROM Monitor mode, verify that the system is in a steady state:
Prepare the DSC:
Anticipate su tantial downtime, including the lo of packet forwarding on the system.
Verify the sanity of the configuration file system using the command
cfs check
in EXEC mode.
Verify that all changes to the active router configuration are saved with the
command in any configuration mode.
Verify that all changes to the active software set are saved with the
i tall commit
command in Administration EXEC mode.
Verify that all i tall commit proce es are complete with the
show i tall committed
command in Administration EXEC mode. This command di lays the committed packages that become active during the next router boot.
Verify that the other nodes in the system are in a steady state:
If a standby DSC is i talled, verify that it is in the ready state with the
show redundancy
command in EXEC mode.
Verify that all available nodes in the system are in IOS XR RUN state with the
show platform
command in EXEC mode.
After you have verified that the system is in a stable state, you can enter ROM Monitor mode by setting the configuration register setting and entering the
command, as described in the following ste .
SUMMARY STEPS
Verify that the router is in a steady state.
Co ect a terminal to the DSC co ole port and log in to the router.
Place the DSC, or all RPs in ROM Monitor mode:
•
Place only the DSC in ROM Monitor mode:
config-register 0x0
•
Or place all RPs in ROM Monitor mode:
config-register 0x0 location all
location all
DETAILED STEPS
Command or Action
Purpose
Ste #160;1 
Verify that the router is in a steady state.
E ures that all configuratio are saved and that no i tallation proce es are ru ing.
•
See the
Ste #160;2 
Co ect a terminal to the DSC co ole port and log in to the router.
Co ects a terminal or PC to the DSC co ole port and establishes a router management se ion.
•
See Co ecting and Communicating with the Router in the
Cisco IOS XR Getting Started Guide
for more information on co ecting a terminal.
Ste #160;3 
Example:
RP/0/RP0/CPU0:router#
Enters administration EXEC mode.
Ste #160;4 
config-register 0x0
config-register 0x0 location all
location all
Examples:
RP/0/RP0/CPU0:router(admin)
config-register
RP/0/RP0/CPU0:router(admin
)# 
RP/0/RP0/CPU0:router
# 
RP/0/RP0/CPU0:router(admin)#
config-register 0x0
location all
RP/0/RP0/CPU0:router(admin)#
reload location all
Enter the following commands to place only the DSC in ROM Monitor mode:
Enter the command
config-register 0x0
to set the configuration register for ROM Monitor mode during the next card reload.
Enter the command
to exit administration EXEC mode.
Enter the command
to reload the DSC and enter ROMMON mode.
If there is a standby DSC, the configuration register on the standby DSC is also set to 0x0. When you place the active RP in ROM Monitor mode, the system fails over to the standby RP, which then becomes the active RP. If both RPs need to be in ROM Monitor mode, co ect to the new active RP and enter the
command.
Or enter the following commands to place all RPs and SCs in ROM Monitor mode:
Enter the
config-register
location
command to reset the configuration register for all RPs in the system.
Enter the
reload location all
command in administration EXEC mode to reload all RPs in the system.
Caution
Resetting the configuration register may change the baud rate for the co ole.
To verify the configuration register setting, enter the
show variables boot
command administration EXEC mode.
Examples
The following examples show how to place the DSC in ROM Monitor mode:
•
•
Verifying the Router State: Example
The following example shows the redundancy roles of both RPs and that both are operating in IOS XR RUN state:
RP/0/RP0/CPU0:router#
show redundancy
Redundancy information for node 0/RP0/CPU0:
==========================================
Node 0/RP0/CPU0 is in ACTIVE role
Partner node (0/RP1/CPU0) is in STANDBY role
Standby node in 0/RP1/CPU0 is ready
RP/0/RP0/CPU0:router#
show platform
Config State
-----------------------------------------------------------------------------
0/1/CPU0
Jacket Card
IOS XR RUN
PWR,NSHUT,MON
MSC(SPA)
4XOC3-POS
PWR,NSHUT,MON
MSC(SPA)
PWR,NSHUT,MON
0/6/CPU0
Jacket Card
IOS XR RUN
PWR,NSHUT,MON
MSC(SPA)
4XOC3-POS
PWR,NSHUT,MON
MSC(SPA)
8XOC3/OC12-POS
PWR,NSHUT,MON
MSC(SPA)
PWR,NSHUT,MON
0/RP0/CPU0
RP(Active)
IOS XR RUN
PWR,NSHUT,MON
0/RP1/CPU0
RP(Standby)
IOS XR RUN
PWR,NSHUT,MON
Placing the DSC in ROM Monitor Mode: Example
The following example shows how to place the RP0 in ROM Monitor mode. This example is for a Cisco XR 12000 Serie #160;Router.
RP/0/0/CPU0:router#
RP/0/0/CPU0:router(admin)#
config-register 0x0
Succe fully set config-register to 0x0 on node 0/0/CPU0
Succe fully set config-register to 0x0 on node 0/1/CPU0
RP/0/0/CPU0:router(admin)#
RP/0/0/CPU0:router#
Proceed with reload? [confirm]
System Bootstrap, Version 12.0(20040624:164256) [a afb-misc1 1.14dev(0.91)] DEV
ELOPMENT SOFTWARE
Copyright (c) 1994-2004 by cisco Systems, Inc.
DRAM DIMM Slot 1: 512M found, Slot 2: Empty
MPC7450 platform with 524288 Kbytes of main memory
rommon 1
Manually Halting the Initialization Proce During System Reload
To force the DSC to stop loading and enter ROM Monitor mode, pre Ctrl-] when you see the following me age:
MBI validation sending request.
HIT Ctrl-]
TYPE 'Send Break'to abort
This me age usually a ears during the first 20 seconds of system startup. Pre the
key combination immediately. This ends your Telnet se ion to the co ole or auxiliary port. Then, type
send break
and pre the
key repeatedly to e ure that the initialization proce sto and the system enters ROMMON.
This operation can be performed only from a terminal directly co ected to the DSC co ole port. See Co ecting and Communicating with the Router in
Cisco IOS XR Getting Started Guide
for more information.
When the DSC is placed in ROMMON, it switches over to the standby DSC, which can then also be placed in ROMMON. Repeat this proce for both RPs.
ROM Monitor Commands
The commands in ROM Monitor are different from those available in the Cisco IOS XR  oftware. You can run ROM Monitor commands only while in ROMMON, and you ca ot run Cisco IOS XR  oftware commands. This section includes the following topics:
•
•
•
Commonly Used ROM Monitor Commands
The commands commonly used in ROM Monitor are summarized in
. For ecific i tructio to use these commands, refer to the relevant procedure in this document.
Table 1-1 Commonly Used ROM Monitor Command #160;
ROMMON Command
Description
Manually boots a vm Cisco IOS XR  oftware image.
image -
config-file-path
Manually boots the Cisco IOS XR  oftware with a temporary alternative Administration configuration file.
image -
config-file-path
Manually boots the Cisco IOS XR  oftware with an alternative secure domain router (SDR) configuration file.
confreg
Changes the config-register setting.
Di lays the available local storage devices (for example, disk0: and disk1:).
Di lays the files on a storage device.
dum laneeeprom
Di lays the cha is serial number in a Cisco CRS-1 router.
Resets the node.
Di lays the currently set ROM Monitor environmental settings.
Saves the new ROM Monitor environmental settings.
Removes an environmental variable setting.
version
Di lays the ROM Monitor version.
Di laying the Available ROM Monitor Commands
describes the available help commands for ROM Monitor mode.
Table 1-2 Help Commands in ROMMON
Command
Description
Di lays a summary of all available ROM Monitor commands.
Di lays information about command syntax.
Commands are case se itive. You can halt any command by pre ing Ctrl-C.
Examples
The following example shows what a ears when you enter the
command on a Cisco CRS-1:
rommon B5
set and di lay aliases command
show_bcm_links
Show Links status on Broadcom Switches
show_bcm
Show Broadcom Switches Information
boot up an external proce confreg
configuration register utility
continue executing a downloaded image
context
di lay the context of a loaded image
list the device table
list files in file system
disa emble i truction stream
serial download a program module
monitor builtin command help
history
monitor command history
meminfo
main memory information
Dump the Serial Presents Detect info from the SDRAM DIMMs
dum laneeeprom
Dump the contents of the back plane
repeat a monitor command
system reset
sca ci0
scan for devices on PCI bus 0
sca ci1
scan for devices on PCI bus 1
di lay the monitor variables
smptest
Test the other CPU on an SMP board
write monitor environment to NVRAM
tftpdnld
tftpdnld no longer available, use boot
unalias
u et an alias
u et a monitor variable
version
di lay rommon software, board, version
writei2c
Write to an I2C device
rommon B2
The following example shows the parameters for the
(directory) command:
rommon 7
bad device name
usage: dir device
Changing the ROM Monitor Prompt
You can change the prompt in ROM Monitor mode by using the
command as shown in the following example:
rommon B1
PS1= CRS1_rp1_rommon !
This can be useful if you are working with multiple routers in ROM Monitor at the same time. This example ecifies that the prompt will be CRS1_rp1_rommo quot; followed by the line number.
Di laying the Configuration Register Setting
To di lay the current configuration register setting, enter the
confreg
command without parameters as follows:
rommon B1
confreg
Configuration Summary
(Virtual Configuration Register: 0x0)
enabled are:
co ole baud: 9600
boot: the ROM Monitor
do you wish to change the configuration? y/n
The configuration register setting is labeled
Virtual Configuration Register
. Enter
to avoid changing the configuration register setting. To change the configuration setting with this command, see the
Environment Variable Settings
The ROM Monitor environment variables define the attributes of the ROM Monitor such as the IP addre for an RP control Ethernet port, or the location of the Cisco IOS XR  oftware and how to load it. Environmental variables are entered like commands and are always followed by the equal sign (=). Environment variable settings are entered in capital letters, followed by a definition. For example:
TURBOBOOT=on,disk0,format
Under normal operating conditio , you will not need to modify these variables. They are cleared or set only when you need to make changes to the way ROM Monitor operates.
This section includes the following topics:
•
•
•
•
Frequently Used Environmental Variables
shows the main ROMMON environmental variables. For i tructio to use these variables, see the relevant i tructio in this document.
Table 1-3 Frequently Used ROM Monitor Environmental Variable #160;
Environmental variable
Description
IP_ADDRESS=
ip_addre On the Cisco CRS-1 RP only. Sets the IP addre for the Management Ethernet interface on the DSC.
IP_SUBNET_MASK=
ip_addre On the Cisco CRS-1 RP only. Sets the su et mask for the Management Ethernet interface on the DSC.
DEFAULT_GATEWAY=
ip_addre On the Cisco CRS-1 RP only. Sets the default gateway that serves the DSC.
TFTP_SERVER=
ip_addre Sets the IP addre of the TFTP server where a bootable software image is located.
TFTP_FILE=
Sets the directory and filename of a a bootable software image.
TURBOBOOT=
on, boot-device, optio Completely replaces the existing software when the router is reloaded.
Identifies the boot software for a node. This variable is usually set automatically when the router boots.
AUX_AUTHEN_LEVEL=
Bypa es
authentication. A reboot is required only on the card that has to bypa authentication.
IOX_ADMIN_CONFIG_FILE=
Permanently changes the location of the default Administration configuration file.
IOX_CONFIG_FILE=
Permanently changes the location of the secure domain router (SDR) configuration file.
IOX_CONFIG_MEDIUM=
Permanently changes the default location where configuration files are saved.
Di laying Environment Variable Settings
To di lay the current environment variable settings, enter the
command as follows:
rommon B1
PS1=rommon !
TFTP_VERBOSE=2
IP_ADDRESS=1.1.1.1
IP_SUBNET_MASK=255.255.0.0
TFTP_SERVER=
DEFAULT_GATEWAY=12.25.0.1
TFTP_FILE=
CONFIG_FILE=
BOOT=disk0:hfr-os-mbi-1.0.0/mbihfr-rp.vm,1;
rommon B2
Entering Environment Variable Settings
Environment variable settings are entered in capital letters, followed by a definition. The following example shows the environmental variables used to configure the control Ethernet port on a Cisco CRS-1 router:
rommon B1
IP_ADDRESS=1.1.1.1
rommon B2
IP_SUBNET_MASK=255.255.254.0
rommon B3
DEFAULT_GATEWAY=1.1.0.1
Saving Environment Variable Settings
To save the current environment variable settings, enter the
command as follows:
rommon B1
Environmental values that are not saved with the
command are discarded whenever the system is reset or booted.
Viewing Cha is Serial Numbers (Cisco CRS-1 Routers)
The cha is serial number is required for multishelf routers and can be read from an SC or RP that is ru ing in ROM Monitor mode. This may be nece ary if the physical label is mi ing or damaged.
You can view the cha is serial numbers using the Cisco IOS XR  oftware. For more information, see Di laying the Cha is Serial Numbers (Cisco CRS-1 Routers) in
Cisco IOS XR
System Management Configuration Guide
Ste #160;1
Attach a co ole to the co ole port of an SC or RP in the cha is. (Only the SC or RP needs to run to perform this procedure. Other cards need not be i erted.)
Ste #160;2
If you have not already done so, a ly power to the cha is.
Ste #160;3
Enter ROM Monitor mode, as described in the
Ste #160;4
Enter the ROMMON command
dum laneeeprom
in the privilege mode of ROMMON to di lay the cha is serial number. In the following example, the serial number is TBC0636606900000:
rommon B3
rommon B4
dum laneeeprom
EEPORM data backplane
00 00 01 e2 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 08 00 45 3b 61 01 04 00 00 00 ........E;a.....
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
54 42 43 30 36 33 36 36 30 36 39 30 30 30 30 30 TBC0636606900000
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
The cha is serial number is di layed in the output to the right (row 00050). A similar number is present for every cha is.
Ste #160;5
Return the router to EXEC mode, as described in the
Exiting ROM Monitor Mode
To exit ROM Monitor mode, you must change the configuration register to 0x102 and reset the RP. This proce can be done by either entering CLI commands or re onding to prompts.
The first RP to enter EXEC mode becomes the DSC. You can determine which RP is the DSC by resetting that card to EXEC mode first and then waiting 1 to 2 minutes to allow it to boot fully. You can also fail over to the standby DSDRSC at any time with the
redundancy switchover
command in EXEC mode.
The following sectio describe ways to exit ROM Monitor mode:
•
•
Resetting to EXEC Mode with CLI Commands
Perform this task to reset the configuration register in ROMMON and start the RP in EXEC mode.
SUMMARY STEPS
confreg 0x102
DETAILED STEPS
Command or Action
Purpose
Ste #160;1 
confreg 0x102
Example:
rommon B1 confreg 0x102
Resets the configuration register to enter EXEC mode when the system is reset.
Ste #160;2 
Example:
rommon B1 reset
Resets and initializes the router.
Resetting the Configuration Register Using Prompts
In ROM Monitor mode, you can change the configuration register value using the configuration register prompts, as shown in this procedure.
SUMMARY STEPS
confreg
Re ond to each prompt as i tructed.
DETAILED STEPS
Command or Action
Purpose
Ste #160;1 
confreg
Example:
rommon B1 confreg
Initiates the configuration register configuration prompts.
Ste #160;2 
Re ond to each prompt as i tructed.
For more information, see the example that follows this procedure.
Ste #160;3 
Example:
rommon B2 reset
Resets and initializes the router.
Examples
The following example shows the commands required and the prompts that a ear when you reset the RP to EXEC mode using the configuration register prompts:
rommon B1
confreg
Configuration Summary
(Virtual Configuration Register: 0x0)
enabled are:
co ole baud: 9600
boot: the ROM Monitor
do you wish to change the configuration? y/n
"diagnostic mode"? y/n
change co ole baud rate? y/n
change the boot characteristics? y/n
enter to boot:
0 = ROM Monitor
1 = MBI Validation Boot Mode
Configuration Summary
(Virtual Configuration Register: 0x102)
enabled are:
co ole baud: 9600
boot: image ecified by the boot system commands
do you wish to change the configuration? y/n
You must reset or power cycle for new config to take effect
rommon B2
Minimum Boot Image (MBI) validation mode causes the RP to boot the startup Cisco IOS XR  oftware and configuration.
Additional References
The following sectio provide references related to the ROM Monitor.
Related Documents
Related Topic
Document Title
Di lay cha is serial numbers (Cisco CRS-1 Routers)
Di laying the Cha is Serial Numbers (Cisco CRS-1 Routers) in
Cisco IOS XR System Management Configuration Guide
Co ecting a terminal to a router.
Co ecting and Communicating with the Router in
Cisco IOS XR Getting Started Guide
Configuring a router with Cisco IOS XR software
Cisco IOS XR Software Documentation:
Technical A istance
Description
The Cisco Technical Su ort we ite contai thousands of pages of searchable technical content, including links to products, technologies, solutio , technical ti , and tools. Registered Cisco.com users can log in from this page to acce even more content.3.1 熟悉ROM Monitor维护路由器
3.1 熟悉ROM Monitor维护路由器
2007-08-29 17:03
《网管员世界》杂志社
电子工业出版社易飞思公司
《网管员世界2007超值精华本》全书分为攻防实战、管理维护、故障诊断、疑难解答4个部分，共精选收录了400多篇实用、精彩的技术文章,该书第三章主要介绍了各种故障诊断，本节介绍了怎样熟悉ROM Monitor来维护路由器。
对于许多初学者来说，Cisco路由器的ROM Monitor常常令人感到陌生甚至望而生畏，原因很简单，一是我们并不经常用到该模式，对其相关操作不熟悉；二是在ROM Monitor模式下的操作失误，往往会对路由器造成致命的伤害（比如破坏flash中的IOS文件，导致系统崩溃），以至于很多人对它束手束脚，望而却步。
其实，ROM Monitor并不复杂，它只是Cisco路由器的一个低级操作系统，通常用于测试和排错，我们只需要花费很少的时间，就可以轻松搞定。下面笔者就以网管员在实际工作中最常遇到的两种需要使用ROM Monitor的情况为例，做一个说明。
情景一：路由器的口令恢复
为了防止别人知道路由器的口令（特别是特权口令），威胁本地网络安全，许多管理员将口令设得特别复杂。但由于路由器的配置完成后，我们就很少再去操作路由器，这样过了一段时间后，我们因为某种需要对路由器进行配置时，就可能因忘记口令而无法进行。
这时候，我们只需要一台PC（操作系统为Windows系列），一条Co ole电缆及相应的接口转换器，然后按照下面的操作，就可以轻松搞定。
（1）设置PC的超级终端，使我们能够使用路由器的Co ole口直接对路由器进行操作（因其过程非常简单，笔者为节省篇幅，将其省略）。
（2）启动路由器，并在前60秒钟内按下“Break”键或“Ctrl+Break”组合键，进入路由器的ROM Monitor模式。
（3）下面以初学者最常接触到的Cisco 2600系列路由器为例，做一些简要描述。
（按下“Ctrl+Break”组合键，进入ROM Monitor模式）
rommon 2 > confreg 0x2142 使用该命令修改路由器的配置寄存器的值，使路由器在下次重启时不要加载启动配置，从而跳过用户口令及特权口令的验证，进入特权模式。
You must reset or power cycle for new config to take effect
rommon 3 > reset 使用该命令重新启动路由器，重启后，系统提示：
Would you like to enter the initial configuration dialog? [yes/no]: n
选择no直接进入CLI模式。
Pre RETURN to get started!
按回车键继续下一步。
Router>en
Router#show version
此时使用show version命令查看配置寄存器的值为0x2142。
Router#copy star ru 使用该命令加载启动配置，然后设置新口令。若没有该步操作，会导致在下次重启后，新口令设置失败。
Router#conf t
Router(config)#config-register 0x2102 路由器下次重启后将加载启动配置，须使用新口令进行验证。
Router(config)#end
Router#copy run star 保存运行配置到启动配置。
Destination filename [startup-config]?
Building configuration...
Cisco 2500、2000、3000、4000和7000系列路由器的口令恢复与上述操作基本相同，其主要差别为，修改配置寄存器的命令为“o/r 0x2142”，以及重启命令为“i”，其他系列的路由器与2600系列基本一致。
情景二：路由器flash中IOS文件的升级或损坏后的恢复 相比较而言，第二种情况更为少见，但也更为严重，它常常发生在对路由器IOS版本升级操作失误或其他软硬件故障原因导致路由器系统崩溃而无法进行工作，致使整个网络瘫痪。
此时，我们常常需要在路由器的ROM Monitor模式下将其修复。
下面就以笔者的一个学生遇到的问题为例，做一下探讨。该学生在对一台Cisco 2600路由器的IOS进行升级时，出现如下故障：
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: ca ot load "flash:"
然后，路由器引导程序再重复上述过程，失败后，进入ROM Monitor模式。
rommon 1 >boot 使用该命令，使路由器重新加载flash中的IOS文件，失败。
boot: ca ot determine first file name on device "flash:"
在确定故障是由路由器不能确定flash中的IOS文件后，我们需要将IOS文件从TFTP Server中恢复到路由器的flash中。此时我们可以通过两种方法完成此任务：其一，使用***了Cisco TFTP Server的PC通过以太网对路由器IOS进行恢复，其二，在ROM Monitor模式下使用xmodem（一种能使用Co ole电缆传输文件的传输协议）命令对路由器IOS进行恢复。
在这里，我们优先使用第一种方法，其步骤如下。
（1）将***了Cisco TFTP Server的PC通过以太网与路由器的以太网接口相连，运行Cisco TFTP Server 程序。
（2）使用超级终端登录路由器Co ole口控制台（路由器已启动，查询故障时已登录），终端屏幕显示如下：
rommon 2 > set 该命令显示路由器相关默认设置：
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/
（3）检查路由器的默认设置，将PC的IP地址改为192.168.1.2（我们同样可以使用命令TFTP_SERVER= 192.168.1.x来修改该设置，但要保证路由器的IP、默认网关与PC的IP在同一网段），这样更简单。
（4）指定要恢复的IOS文件名，并保证该文件在Cisco TFTP Server根目录下。 Rommon 3 > TFTP_FILE=/c2600-i-mz.121-3.T.bin 不要忘记加上扩展文件名.bin。
（5）开始恢复IOS文件：
rommon 4 > tftpdnld 执行该命令从TFTF Server下载IOS文件到flash，该命令仅适用于Cisco 2600系列路由器。
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 partitio on flash will be lost!
Do you wish to continue? y/n: [n]: y
Receiving /c2600-i-mz.121-3.T.bin from 192.168.1.2
（确认后，路由器开始下载IOS文件，省略多行）
File reception completed.
Copying file /c2600-i-mz.121-3.T.bin to flash.
Erasing flash at 0x60fc0000
program flash location 0x60160000
（6）重新启动路由器，运行新的IOS。
rommon 5 > reset
（下面为正常的启动过程，故省略）
Cisco ROM Monitor模式下还有其他很多不同功能的命令，我们可以使用它们对路由器进行一系列的测试与排错，有关该模式的详细说明请访问Cisco站点
进行相关搜索，搜索关键字为Using the ROM Monitor。
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对于许多初学者来说，Cisco路由器的ROM Monitor常常令人感到陌生甚至望而生畏，原因很简单，一是我们并不经常用到该模式，对其相关操作不熟悉；二是在ROM Monitor模式下的操作失误，往往会对路由器造成致命的伤害（比如破坏flash中的IOS文件，导致系统崩溃），以至于很多人对它束手束脚，望而却步。 　　对于许多初学者来说，Cisco路由器的ROM Monitor常常令人感到陌生甚至望而生畏，原因很简单，一是我们并不经常用到该模式，对其相关操作不熟悉；二是在ROM Monitor模式下的操作失误，往往会对路由器造成致命的伤害（比如破坏flash中的IOS文件，导致系统崩溃），以至于很多人对它束手束脚，望而却步。 其实，ROM Monitor并不复杂，它只是Cisco路由器的一个低级操作系统，通常用于测试和排错，我们只需花费很少的时间，就可以轻松搞定。下面笔者就以网管员在实际工作中最常遇到的两种需要使用ROM Monitor的情况为例，做一个说明。 情景一：路由器的口令恢复 为了防止别人知道路由器的口令（特别是特权口令），威胁本地网络安全，许多管理员将口令设得特别复杂。但由于路由器的配置完成后，我们就很少再去操作路由器，这样过了一段时间后，我们因为某种需要需对路由器进行配置时，就可能因忘记口令而无法进行。 这时候，我们只需要一台PC机（操作系统为
Windows
系列），一条Co ole电缆及相应的接口转换器，然后按照下面的操作，就可以轻松搞定。 1. 设置PC机的超级终端，使我们能够使用路由器的Co ole口直接对路由器进行操作（因其过程非常简单，笔者为节省篇幅，将其省略）。 2.启动路由器，并在前60秒内按下Break或Ctrl+Break键，进入路由器的ROM Monitor模式。 3.下面以初学者最常接触到的Cisco 2600系列路由器为例，做一些简要描述。 （按下Ctrl+Break键，进入ROM Monitor模式） rommon 2 > confreg 0x2142 使用该命令修改路由器的配置寄存器的值，使路由器在下次重启时不要加载启动配置，从而跳过用户口令及特权口令的验证，进入特权模式。 You must reset or power cycle for new config to take effect rommon 3 > reset 使用该命令重新启动路由器，重启后，系统提示： Would you like to enter the initial configuration dialog？ [yes/no]： n 选择no直接进入CLI模式 Pre RETURN to get started！ 按回车键继续下一步。 Router>en Router#show version 此时使用show version命令查看配置寄存器的值为0x2142. Router#copy star run 使用该命令加载启动配置，然后设置新口令。若没有该步操作，会导致在下次重启后，新口令设置失败。 Router#conf t Router（config）#config-register 0x2102 路由器下次重启后将加载启动配置，需使用新口令进行验证。 Router（config）#end Router#copy run star 保存运行配置到启动配置 Destination filename [startup-config]？ Building configuration…… [OK] 提示：Cisco 2500、2000、3000、4000和7000系列路由器的口令恢复与上述操作基本相同，其主要差别为修改配置寄存器的命令为“o/r 0x2142”，以及重启命令为“i”，其他系列的路由器与2600系列基本一致。 情景二：路由器flash中
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