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• Register setting 0x2010—Configures <strong>the</strong> router <strong>to</strong> check<br />

NVRAM and boot directly in<strong>to</strong> ROM moni<strong>to</strong>r.<br />

• Register setting 0x8000—Configures <strong>the</strong> router<br />

(2500,4000,7x00) and loads <strong>the</strong> router in<strong>to</strong> diagnostic mode.<br />

Setting 0xA042 is used on 4500 and 4700 series routers.<br />

• Register setting 0x2101—Loads <strong>the</strong> IOS from ROM, and <strong>the</strong><br />

NVRAM configuration is loaded in<strong>to</strong> RAM as <strong>the</strong> running<br />

configuration. This is useful for performing IOS upgrades or if<br />

<strong>the</strong> flash IOS image is corrupted. Not all routers have a<br />

ROM-based IOS <strong>to</strong> boot from, so this option only works on those<br />

that do (2500, 4000, 7x00). If this setting is used on routers<br />

that do not have an IOS in ROM, RFF IOS-based routers will<br />

boot with flash in read/write mode. RFR IOS-based routers will<br />

just read <strong>the</strong> IOS in flash, which is always in read/write mode.<br />

See <strong>the</strong> section "Upgrading Your Router's IOS" for more<br />

information.<br />

• Register setting 0x2102—This is <strong>the</strong> Cisco default conf-reg<br />

setting. The router loads <strong>the</strong> IOS from flash or <strong>the</strong> boot system<br />

source specified in NVRAM. After <strong>the</strong> IOS is loaded, <strong>the</strong> startup<br />

configuration is loaded from NVRAM <strong>to</strong> RAM as <strong>the</strong> running<br />

configuration. By default, console break option is disabled once<br />

<strong>the</strong> IOS is loaded, so if you want <strong>to</strong> have it enabled, use<br />

conf-reg setting 0x2002 instead.<br />

• Register setting 0x2141—Tells <strong>the</strong> router <strong>to</strong> load <strong>the</strong> IOS from<br />

ROM (Cisco 2500, 4x00, and 7x00) and ignore <strong>the</strong> configuration<br />

in NVRAM. Because <strong>the</strong> startup configuration is not copied <strong>to</strong><br />

DRAM, <strong>the</strong> router starts in setup mode. This is great if <strong>the</strong> IOS<br />

image is damaged, or if you need <strong>to</strong> perform an IOS upgrade on<br />

an RFF and have no local TFTP server.<br />

• Register setting 0x2142—The router loads <strong>the</strong> IOS from flash<br />

and ignores <strong>the</strong> NVRAM (just like setting 0x2141). This is <strong>the</strong><br />

Cisco recommended setting <strong>to</strong> use for password recovery. A<br />

choice exists between two recovery processes: brute force or<br />

subtle. This brute force method erases <strong>the</strong> router configuration<br />

completely. If you have a backup of <strong>the</strong> router configuration or<br />

do not need any of <strong>the</strong> configuration information, this setting<br />

works fine.<br />

To change <strong>the</strong> conf-reg setting after <strong>the</strong> router is up and running use<br />

<strong>the</strong> following steps:

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