Chapter 4 Troubleshooting the Installation
Performing Other Configuration Tasks
4-4
Cisco 12006 and Cisco 12406 Router Installation and Configuration Guide
OL-11497-03
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)#].
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.
02 to 0F On power up, the system boots automatically from a default Cisco
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.
Note Note: A Cisco 12006 or Cisco 12406 Router is typically delivered from
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.
Table 4-2 Boot Field and Meanings (continued)
Boot Field Definition