Cisco 12406 User Manual
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Troubleshooting the Installation
This chapter provides troubleshooting guidelines for Cisco 12006 and
Cisco 12406 Routers. If the solutions provided in this chapter do not make the
router fully functional, contact your Cisco service representative for assistance.
• Performing Other Configuration Tasks, page 4-1
• Problem Solving with Subsystems, page 4-14
Performing Other Configuration Tasks
This section describes the following additional configuration tasks.
• Configuring the Software Configuration Register, page 4-1
• Recovering a Lost Password, page 4-11
4
Configuring the Software Configuration Register
The software configuration register is a 16-bit register in NVRAM that you use to
define specific system parameters. You can set or change the contents of this
register to accomplish the following tasks:
• Define boot sources for the default Cisco IOS software, assigning them in the
following order of precedence:
–
Flash memory card inserted in PCMCIA slot 0
–
TFTP server on the network
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Performing Other Configuration Tasks
–
Flash memory SIMM (NVRAM) on the RP
–
Boot image stored within the operating environment, which you access
by using an appropriate form of the boot command entered at the ROM
monitor prompt (
• Define a default boot filename.
• Enable or disable the Break function.
• Control broadcast addresses.
• Set the console terminal baud rate.
• Force an automatic boot using a boot image.
When you first power on the router, a boot image called the RP ROM monitor
is executed, and the ROM monitor prompt (
prompt, you have access to a limited set of commands that enable you to set
values in the software configuration register and to perform other tasks.
The RP ROM monitor is loaded into the RP Flash ROM when the RP is
manufactured. You can use it to boot the system from local Flash memory
devices. The RP ROM monitor software can be upgraded in the field, if
necessary.
• Read boot system commands from the configuration file stored in NVRAM.
Table 4-1 defines the bits in the software configuration register.
Chapter 4 Troubleshooting the Installation
rommon>)
rommon>) is displayed. At this
4-2
Caution To avoid confusion and possibly halting the system, remember that valid software
configuration register values may be combinations of settings, rather than the
individual settings listed in Table 4-1 . For example, the factory default value
0x0102 for the software configuration register is a composite of several settings.
Table 4-1 Software Configuration Register Bit Meanings
Hexadecimal
1
Bit Number
00 to 03 0x0000 to
Value Definition/Function
Comprises the boot field for defining the source of
0x000F
a default Cisco IOS software image required to run
the router
06 0x0040 Causes system software to ignore the contents of
NVRAM
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Table 4-1 Software Configuration Register Bit Meanings (continued)
Bit Number
1
07 0x0080 Enables the OEM
08 0x0100 Disables the Break function
09 0x0200 Uses a secondary bootstrap
10 0x0400 Broadcasts Internet Protocol (IP) with all zeros
11 and 12 0x0800 to
13 0x2000 Boots the default Flash memory software if the
14 0x4000 Excludes network numbers from IP broadcasts
15 0x8000 Enables diagnostic messages and ignores the
1. The factory default value for the software configuration register is 0x0102. This value is a
combination of binary bit 8 = 0x0100 and binary bits 00 through 03 = 0x0002.
2. OEM = original equipment manufacturer.
Hexadecimal
Value Definition/Function
Defines the console baud rate (the default setting
0x1000
is 9600 bps)
network boot fails
contents of NVRAM
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2
bit
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Table 4-2 specifies the content of the boot field, which defines a source for
booting the default Cisco IOS software image required to run the router. The
content of the boot field is specified as a binary number.
Table 4-2 Boot Field and Meanings
Boot Field Definition
00 On power up, the system remains at the ROM monitor prompt
(
rommon>) awaiting a user command to boot the system manually.
01 On power up, the system automatically boots the first system image
found in the onboard Flash memory SIMM on the RP.
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Table 4-2 Boot Field and Meanings (continued)
Boot Field Definition
02 to 0F On power up, the system boots automatically from a default Cisco
Note Note: A Cisco 12006 or Cisco 12406 Router is typically delivered from
Boot Field Settings
The four low-order bits of the software configuration register (bits 3, 2, 1, and 0)
form a boot field that defines the source of a Cisco IOS software image for booting
the router. You can set or change the contents of the boot field by issuing the
config-register command at the global configuration mode prompt
[
router(config)#].
Chapter 4 Troubleshooting the Installation
IOS software image stored on a TFTP server in the network. For
this setting, it is assumed that the Ethernet port on the RP is
configured and operational. This setting also enables boot system
commands that override the default filename.
the factory with a boot image in the boot flash and a Flash card
containing a suitable working Cisco IOS image. If you need a Cisco IOS
upgrade, you should FTP the appropriate Cisco IOS image from CCO.
4-4
Note The factory default configuration register setting for an RP shipped in a router or
an RP shipped as a field-replaceable unit is 0x0102.
When the boot field is set to either 0 or 1 (0000 or 0001), the system ignores any
boot instructions in the system configuration file and one of the following occurs,
depending on the boot field setting:
• When the boot field is set to 0, you must boot the operating system manually
by entering the boot command at the ROM monitor prompt (
rommon>). You
can enter the boot command with or without arguments.
If you enter the boot command without an argument (that is, without
specifying a file or any other boot instructions), the system automatically
boots using the default image in the Flash memory SIMM on the RP.
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If you enter the boot command with arguments (that is, by instructing the
system to boot from a specific source), you have these options:
–
You can instruct the system to boot from a specific Flash SIMM image
by entering the boot bootflash:filename command, or from a specific
image stored on a PCMCIA Flash memory card by entering the
boot slot #: imagename command.
–
You can instruct the system to boot from a network TFTP server either
by sending broadcast TFTP requests by entering a boot filename
command, or by sending a direct request to a specific network TFTP
server by issuing a boot filename ip-address command.
• When the boot field is set to 1, the system automatically boots using the first
image found in the onboard Flash SIMM on the RP.
• When the boot field is set to a bit pattern other than 0 or 1, the router uses the
software configuration register settings to compute the filename of a default
system image stored on a network TFTP server. It then uses that system image
to boot the router. But if the configuration file contains boot instructions, the
system uses these instructions to boot the system, rather than using the
filename it computed from the software configuration register settings.
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To form this filename, the system starts with cisco and links the octal
equivalent of the boot field value and the processor type in this format:
cisco<bootfieldvalue>-<processorname>
For example, the filename formation process would yield a range of filenames
such as the following:
cisco2-grp
.
.
.
cisco17-grp
or
cisco2-prp
.
.
.
cisco17-prp
The system would use one of the filenames in this range to boot a default system
image stored on a network TFTP server.
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Note If a bootable Cisco IOS software image exists in a Flash memory card inserted in
PCMCIA slot 0 or slot 1, the software configuration register boot field setting is
overridden. The system then boots from the Cisco IOS software image in the Flash
memory card, rather than from a network TFTP image (that is, from a computed
filename in the range from cisco2-grp through cisco17-grp or cisco2-prp through
cisco17-prp).
Configuration Register Settings
To change the software configuration register settings while running system
software, follow these steps:
Step 1 Enter the enable command and your password at the user EXEC mode prompt to
enter privileged EXEC mode:
Router> enable
Password: <password>
Router#
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Step 2 Enter the configure terminal command at the privileged EXEC mode prompt on
the system console to enter global configuration mode, as shown in the following
example:
Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#
Step 3 Set the contents of the software configuration register by entering the
config-register value command at the global configuration mode prompt, where
value is a hexadecimal number preceded by 0x, as in the following:
Router(config)# config-register 0xvalue
Consult the hexadecimal column in Table 4-1 on page 4-2 for the possible settings
to enter as the four-bit value parameter.
Step 4 Exit global configuration mode by entering Ctrl-Z.
Router(config)# config-register 0xvalue
Router(config)# Ctrl-Z
Router#
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This command sequence saves the new contents of the software configuration
register to NVRAM, but these new settings do not take effect until you reload or
reboot the router.
Step 5 Enter the show version privileged EXEC command to display the software
configuration register value currently in effect. This value will be used the next
time the router reloads. The value is displayed on the last line of the screen
display, as in the following example:
Router# show version
.
.
.
Configuration register is 0x141 (will be 0x102 at next reload)
Step 6 Save the software configuration register settings as described in the “Problem
Solving with Subsystems” section on page 4-14.
Note Configuration register changes take effect only after the system reloads,
such as when you enter a reload command from the console.
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Step 7 Reboot the router.
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Bits in the Software Configuration Register
This section provides more detailed descriptions of the significance of the bits in
the software configuration register and how they interact during the boot process.
As described in the “Boot Field Settings” section on page 4-4, the boot field
setting determines the source of the Cisco IOS software image that is used to boot
the router. If you set the boot field value to 0 (0x0000), you must boot the
operating system manually by entering the boot command at the ROM monitor
prompt (
If you set the boot field value to 0x2 through 0xF and a valid boot system
command is stored in the configuration file, the router boots the Cisco IOS
software image as directed by that value. If no boot system command is present
in the configuration file, the router forms a default boot filename and attempts to
acquire that file from a network TFTP server.
In the following example, the software configuration register is set to boot the
router from the Flash memory SIMM on the RP and to ignore the Break function
at the next reboot of the system:
Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)# config-register 0x0102
Router(config)# boot system flash filename
Ctrl-Z
Router#
rommon>) on the system console.
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With the configuration register set to 0x0102, the system computes a default boot
filename. In forming this filename, the system starts with cisco and appends the
octal equivalent of the boot field number, a hyphen, and the processor type (grp
or prp).
Table 4-3 lists the range of possible computed default filenames for booting over
the network. However, a valid boot system configuration command stored in the
NVRAM configuration file overrides any computed default filename for booting
over the network.
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Note If a bootable Cisco IOS software image exists in a Flash memory card installed in
PCMCIA slot 0 or 1, the configuration register setting is overridden, and the
bootable Cisco IOS software image will be booted instead of the default
TFTP-bootable Cisco IOS software image (cisco2-grp through cisco17-grp or
cisco2-prp through cisco17-prp).
Table 4-3 Default Boot Filenames
Action/Filename Bit 3 Bit 2 Bit 1 Bit 0
Bootstrap mode 0 0 0 0
Default software 0 0 0 1
cisco2-grp or cisco2-prp 0 0 1 0
cisco3-grp or cisco3-prp 0 0 1 1
cisco4-grp or cisco4-prp 0 1 0 0
cisco5-grp or cisco5-prp 0 1 0 1
cisco6-grp or cisco6-prp 0 1 1 0
cisco7-grp or cisco7-prp 0 1 1 1
cisco10-grp or cisco10-prp 1 0 0 0
cisco11-grp or cisco11-prp 1 0 0 1
cisco12-grp or cisco12-prp 1 0 1 0
cisco13-grp or cisco13-prp 1 0 1 1
cisco14-grp or cisco14-prp 1 1 0 0
cisco15-grp or cisco15-prp 1 1 0 1
cisco16-grp or cisco16-prp 1 1 1 0
cisco17-grp or cisco17-prp 1 1 1 1
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The significance of bits 8 through 14 in the software configuration register
follows.
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Bit 8—Bit 8 of the software configuration register controls the console Break key.
Setting bit 8 causes the system to ignore the console Break key. This is the factory
default. Conversely, clearing bit 8 causes the system to interpret a Break
keystroke as a command to halt normal system operation and force the system into
ROM monitor mode. Regardless of the setting of the Break enable bit in the
software configuration register, pressing the Break key during approximately the
first 5 seconds of booting causes a return to the ROM monitor.
Bit 9—Bit 9 is not used.
Bits 10 and 14—Bit 10 of the software configuration register controls the host
portion of the IP broadcast address. Setting bit 10 causes the processor to use all
zeros in the host portion of the IP broadcast address; clearing bit 10 (the factory
default) causes the processor to use all ones. Bit 10 interacts with bit 14, which
controls the network and subnet portions of the IP broadcast address. Tab le 4 -4
shows the combined effect of bits 10 and 14.
Table 4-4 Configuration Register Settings for Broadcast Address
Bit 10 Bit 14 Address (<net> <host>)
Off Off <ones> <ones>
On Off <zeros> <zeros>
On On <net> <zeros>
Off On <net> <ones>
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Destination
4-10
Bits 11 and 12—Bits 11 and 12 of the software configuration register determine
the data transmission rate of the console terminal. Tab le 4- 5 shows the bit settings
for the four available data transmission rates. The factory-set default data
transmission rate is 9600 bps.
Table 4-5 System Console Terminal Data Transmission Rate Settings
Bit 12 Bit 11 Data Transmission Rate (bps)
0 0 9600
0 1 4800
1 0 1200
1 1 2400
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Bit 13—Bit 13 of the software configuration register determines the system
response to a bootload failure. Setting bit 13 causes the system to load Cisco IOS
software from Flash memory after five unsuccessful attempts to load a boot file
from the network TFTP server. Clearing bit 13 causes the system to continue
attempting to load a boot file from the network TFTP server indefinitely. Bit 13 is
set to 0 as the default at the factory.
Recovering a Lost Password
This section provides information on how to recover a lost password.
Note If the enable password is encrypted, the following procedure will not work for
password recovery, and you will have to reconfigure the system before attempting
a reboot. To reconfigure the system, use the displayed configuration, which is
shown using the show startup-config command in privileged EXEC mode,
shown in Step 11.
To recover a lost password, follow these steps:
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Step 1 Attach an ASCII terminal to the RP console port.
Step 2 Configure the terminal to operate at 9600 bps, 8 data bits, no parity, 2 stop bits (or
whatever settings the console port is set to).
Step 3 Enter the show version command at the privileged EXEC mode prompt to display
the existing software configuration register value.
Router# show version
.
.
.
The current configuration setting appears in the last line of the show version
command output. Write this value on paper for use in Step 13.
Step 4 If the Break function is disabled, turn off power to the power supplies, wait
5 seconds, then restore power.
If the Break function is enabled, press the Break key or send a break by holding
down the Control key and pressing the right square bracket key (Ctrl-]).
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