Config-register Command on CISCO Router/Switch

Command

Config-register

Use

This command is used to modify what configuration files the router reads as it is starting up.
This is most commonly used for password recovery purposes.

Syntax

R1(config)#config-register <value>

Optional values

0x2102 This tells the router to startup normally, reading the config in NVRAM
0x2142 This tells the router to ignore the contents of NVRAM and load a default config.

Example

In this example, we will change the configuartion register to 0x2142.

2611XM#show version | in 0x
Configuration register is 0x2102

2611XM#conf t
Enter configuration commands, one per line. End with CNTL/Z.
2611XM(config)#config-register 0x2142

To test this, we reloaded the 2611XM router and we see it booted with a default configuration.

2611XM(config)#do reload
Proceed with reload? [confirm]
*Jul 18 05:23:05.182: %SYS-5-RELOAD: Reload requested by drobb on vty0 (10.10.2. 5). Reload Reason: Reload Command.
[Connection to 10.10.2.5 closed by local host]
2611XM#
System Bootstrap, Version 12.2(8r) [cmong 8r], RELEASE SOFTWARE (fc1)
Copyright (c) 2003 by cisco Systems, Inc.
C2600 platform with 262144 Kbytes of main memory

program load complete, entry point: 0x80008000, size: 0x1c8a09c
Self decompressing the image : ################################################# ################################################################################ ################################################################################ ################################################################################ ################################################################################ ################################################################################ ############ [OK]

Smart Init is enabled
smart init is sizing iomem
ID MEMORY_REQ TYPE
00036B 0X00103980 C2611XM Dual Fast Ethernet
0X00098670 public buffer pools
0X00211000 public particle pools
TOTAL: 0X003ACFF0

If any of the above Memory Requirements are
“UNKNOWN”, you may be using an unsupported
configuration or there is a software problem and
system operation may be compromised.
Rounded IOMEM up to: 3Mb.
Using 1 percent iomem. [3Mb/256Mb]

Increasing IOMEM up to: 8Mb
Restricted Rights Legend

Use, duplication, or disclosure by the Government is
subject to restrictions as set forth in subparagraph
(c) of the Commercial Computer Software – Restricted
Rights clause at FAR sec. 52.227-19 and subparagraph
(c) (1) (ii) of the Rights in Technical Data and Computer
Software clause at DFARS sec. 252.227-7013.

cisco Systems, Inc.
170 West Tasman Drive
San Jose, California 95134-1706

Cisco IOS Software, C2600 Software (C2600-ADVENTERPRISEK9-M), Version 12.4(17), RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2007 by Cisco Systems, Inc.
Compiled Fri 07-Sep-07 16:05 by prod_rel_team
Image text-base: 0x800080F8, data-base: 0x82B92F54

This product contains cryptographic features and is subject to United
States and local country laws governing import, export, transfer and
use. Delivery of Cisco cryptographic products does not imply
third-party authority to import, export, distribute or use encryption.
Importers, exporters, distributors and users are responsible for
compliance with U.S. and local country laws. By using this product you
agree to comply with applicable laws and regulations. If you are unable
to comply with U.S. and local laws, return this product immediately.

A summary of U.S. laws governing Cisco cryptographic products may be found at:
http://www.cisco.com/wwl/export/crypto/tool/stqrg.html

If you require further assistance please contact us by sending email to
export@cisco.com.

Cisco 2611XM (MPC860P) processor (revision 4.1) with 253952K/8192K bytes of memo ry.
Processor board ID FCZ094571UF
M860 processor: part number 5, mask 2
2 FastEthernet interfaces
32K bytes of NVRAM.
32768K bytes of processor board System flash (Read/Write)

— System Configuration Dialog —

Would you like to enter the initial configuration dialog? [yes/no]: no

Press RETURN to get started!

*Mar 1 00:00:07.584: %LINEPROTO-5-UPDOWN: Line protocol on Interface VoIP-Null0 , changed state to up
*Mar 1 00:00:29.324: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state t o up
*Mar 1 00:00:29.324: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state t o up
*Mar 1 00:00:30.325: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthern et0/0, changed state to down
*Mar 1 00:00:30.325: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthern et0/1, changed state to down
*Jul 18 05:23:06.650: %LINK-5-CHANGED: Interface FastEthernet0/0, changed state to administratively down
*Jul 18 05:23:06.650: %LINK-5-CHANGED: Interface FastEthernet0/1, changed state to administratively down
*Jul 18 05:23:07.508: %SYS-5-RESTART: System restarted —
Cisco IOS Software, C2600 Software (C2600-ADVENTERPRISEK9-M), Version 12.4(17), RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2007 by Cisco Systems, Inc.
Compiled Fri 07-Sep-07 16:
Router>
Route05 by prod_rel_team
*Jul 18 05:23:07.512: %SNMP-5-COLDSTART: SNMP agent on host Router is undergoing a cold startr>
Router>en
Router#copy start run
Destination filename [running-config]?

Slot is empty or does not support clock participate
WIC slot is empty or does not support clock participate
8575 bytes copied in 17.773 secs (482 bytes/sec)
2611XM#
*Jul 18 05:23:36.379: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback0, changed state to up
*Jul 18 05:23:36.379: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback44, changed state to up
*Jul 18 05:23:38.062: %LINEPROTO-5-UPDOWN: Line protocol on Interface NVI0, changed state to up
*Jul 18 05:23:39.332: %HA_EM-4-FMPD_NO_EVENT: No event configured for applet INTDOWN
*Jul 18 05:23:36.163: %CRYPTO-6-ISAKMP_ON_OFF: ISAKMP is ON

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