The document discusses Cisco IOS software configuration registers, which are used to identify where a Cisco router boots its IOS image from. It explains that the configuration register value determines the boot option, such as booting from flash memory, a TFTP server, or ROM monitor mode. It also shows commands for configuring the boot system and checking the current configuration register value.

1. Managing the Configuration Environment Copyright © 1998 Cisco Systems, Inc. ICRC_revision_11.3

2. Locating the Cisco IOS Software Configuration Registers Registers in NVRAM for modifying fundamental Cisco IOS software Identifies where to boot Cisco IOS image (for example, use config-mode commands)

3. Locating the Cisco IOS Software Configuration Registers Registers in NVRAM for modifying fundamental Cisco IOS software Identifies where to boot Cisco IOS image (for example, use config-mode commands) Router# configure terminal Router(config)# boot system flash IOS_filename Router(config)# boot system tftp IOS_filename tftp_address Router(config)# boot system rom [Ctrl-Z] Router# copy running-config startup-config

4. Locating the Cisco IOS Software Configuration Registers Registers in NVRAM for modifying fundamental Cisco IOS software Identifies where to boot Cisco IOS image (for example, use config-mode commands) Router# configure terminal Router(config)# boot system flash IOS_filename Router(config)# boot system tftp IOS_filename tftp_address Router(config)# boot system rom [Ctrl-Z] Router# copy running-config startup-config Boot system commands not found In NVRAM

5. Locating the Cisco IOS Software Configuration Registers Registers in NVRAM for modifying fundamental Cisco IOS software Identifies where to boot Cisco IOS image (for example, use config-mode commands) Router# configure terminal Router(config)# boot system flash IOS_filename Router(config)# boot system tftp IOS_filename tftp_address Router(config)# boot system rom [Ctrl-Z] Router# copy running-config startup-config Boot system commands not found In NVRAM Get default Cisco IOS software from Flash

6. Locating the Cisco IOS Software Configuration Registers Registers in NVRAM for modifying fundamental Cisco IOS software Identifies where to boot Cisco IOS image (for example, use config-mode commands) Router# configure terminal Router(config)# boot system flash IOS_filename Router(config)# boot system tftp IOS_filename tftp_address Router(config)# boot system rom [Ctrl-Z] Router# copy running-config startup-config Boot system commands not found In NVRAM Get default Cisco IOS software from Flash Flash memory empty

7. Locating the Cisco IOS Software Configuration Registers Registers in NVRAM for modifying fundamental Cisco IOS software Identifies where to boot Cisco IOS image (for example, use config-mode commands) Router# configure terminal Router(config)# boot system flash IOS_filename Router(config)# boot system tftp IOS_filename tftp_address Router(config)# boot system rom [Ctrl-Z] Router# copy running-config startup-config Boot system commands not found In NVRAM Get default Cisco IOS software from Flash Flash memory empty Get default Cisco IOS software from TFTP server

8. Locating the Cisco IOS Software ROM monitor Configuration Registers Registers in NVRAM for modifying fundamental Cisco IOS software Identifies where to boot Cisco IOS image (for example, use config-mode commands) Router# configure terminal Router(config)# boot system flash IOS_filename Router(config)# boot system tftp IOS_filename tftp_address Router(config)# boot system rom [Ctrl-Z] Router# copy running-config startup-config Boot system commands not found In NVRAM Get default Cisco IOS software from Flash Flash memory empty Get default Cisco IOS software from TFTP server

9. Determining the Current Configuration Register Value Router# show version IOS (tm) 2500 Software (C2500-JS-L), Version 11.2 (6), RELEASE SOFTWARE (fc1) Copyright (c) 1986-1997 by cisco Systems, Inc. Compiled Tue 06-May-97 16:17 by kuong Image text-base: 0x0303ED8C, data-base: 0x00001000 ROM: System Bootstrap, Version 5.2(8a), RELEASE SOFTWARE ROM: 3000 Bootstrap Software (IGS-RXBOOT), version 10.2 (8a), RELEASE SOFTWARE (fc1) Router uptime is 21 hours, 13 minutes System restarted by reload System image file is "flash:c2500-js-l.112-6.bin", booted via flash Configuration register is 0x2102 . . .

10. Configuration Register bits 3, 2, 1, and 0 set boot option Configuration Register Values Router#configure terminal Router(config)# config-register 0x2102 [Ctrl-Z] Router#reload

11. Configuration Register bits 3, 2, 1, and 0 set boot option Configuration Register Values Configuration-Register Value 0x0 Meaning Use ROM monitor mode (Manually boot using the b command) Router#configure terminal Router(config)# config-register 0x2102 [Ctrl-Z] Router#reload

12. Configuration Register bits 3, 2, 1, and 0 set boot option Configuration Register Values Configuration-Register Value 0x0 0x1 Meaning Use ROM monitor mode (Manually boot using the b command) Automatically boot from ROM (Provides IOS subset) Router#configure terminal Router(config)# config-register 0x2102 [Ctrl-Z] Router#reload

13. Configuration Register bits 3, 2, 1, and 0 set boot option Check Configuration Register setting with show version Configuration Register Values Configuration-Register Value 0x0 0x2 to 0xF 0x1 Meaning Use ROM monitor mode (Manually boot using the b command) Examine NVRAM for boot system commands (0x2 default if router has Flash) Automatically boot from ROM (Provides IOS subset) Router#configure terminal Router(config)# config-register 0x2102 [Ctrl-Z] Router#reload

14. Boot System Options in Software Router#configure terminal Router(config)# boot system flash c2500-js-l [Ctrl-Z] Router#copy running-config startup-config Flash

15. Boot System Options in Software Router#configure terminal Router(config)# boot system flash c2500-js-l [Ctrl-Z] Router#copy running-config startup-config Flash Network Router#configure terminal Router(config)# boot system tftp test.exe 172.16.13.111 [Ctrl-Z] Router#copy running-config startup-config

16. Boot System Options in Software Router#configure terminal Router(config)# boot system flash c2500-js-l [Ctrl-Z] Router#copy running-config startup-config Flash Network Router#configure terminal Router(config)# boot system tftp test.exe 172.16.13.111 [Ctrl-Z] Router#copy running-config startup-config ROM Router#configure terminal Router(config)# boot system rom [Ctrl-Z] Router#copy running-config startup-config