Router(config)# config-register 0x2102\n<\/code><\/pre>\nTo configure the router to ignore NVRAM upon the next reboot:<\/p>\n
Router(config)# config-register 0x2142\n<\/code><\/pre>\n<\/span>Step 3: Exit Configuration Mode<\/span><\/h3>\nReturn to privileged EXEC mode:<\/p>\n
Router(config)# exit\nRouter#\n<\/code><\/pre>\n<\/span>Step 4: Verify the Pending Setting<\/span><\/h3>\nConfirm that IOS has registered the upcoming value:<\/p>\n
Router# show version | include Configuration register\nConfiguration register is 0x2102 (will be 0x2142 at next reload)\n<\/code><\/pre>\n<\/span>Step 5: Save Configuration and Reload (If Applicable)<\/span><\/h3>\nIf you made changes to the running configuration that must persist, save them to NVRAM. When ready to apply the register setting, initiate a system reload:<\/p>\n
Router# copy running-config startup-config\nDestination filename [startup-config]? [Enter]\nBuilding configuration...\n[OK]\nRouter# reload\nProceed with reload? [confirm] [Enter]\n<\/code><\/pre>\n
\n<\/span>0x2102 vs. 0x2142: Feature and Use Case Comparison<\/span><\/h2>\nThe two most widely used configuration register values across enterprise routing hardware are 0x2102<\/code> and 0x2142<\/code>. Selecting the wrong value can cause a router to come online completely unconfigured.<\/p>\n\n\n\n| Feature \/ Behavior<\/th>\n | Register Value 0x2102<\/code><\/th>\nRegister Value 0x2142<\/code><\/th>\n<\/tr>\n<\/thead>\n\n\nOperational State<\/strong><\/td>\n| Normal Production Mode<\/td>\n | Disaster Recovery \/ Maintenance Mode<\/td>\n<\/tr>\n | \nStartup-Config in NVRAM<\/strong><\/td>\nLoaded and executed<\/strong> automatically at boot<\/td>\nIgnored<\/strong> during system boot<\/td>\n<\/tr>\n\nBit 6 State (0x0040)<\/strong><\/td>\n0<\/code> (Cleared)<\/td>\n1<\/code> (Set)<\/td>\n<\/tr>\n\nBoot Field (Bits 0\u20133)<\/strong><\/td>\n0x2<\/code> (Parses boot system<\/code> commands or boots Flash)<\/td>\n0x2<\/code> (Boots system image from Flash)<\/td>\n<\/tr>\n\nInitial CLI Prompt<\/strong><\/td>\nStandard hostname prompt (e.g., Branch-R1><\/code>)<\/td>\nInitial Configuration Dialog prompt (setup mode<\/code>)<\/td>\n<\/tr>\n\nConsole Baud Rate<\/strong><\/td>\n| 9600 bps<\/td>\n | 9600 bps<\/td>\n<\/tr>\n | \nConsole Break Key<\/strong><\/td>\n| Enabled during boot sequence<\/td>\n | Enabled during boot sequence<\/td>\n<\/tr>\n | \nPrimary Use Case<\/strong><\/td>\n| Day-to-day enterprise routing operations<\/td>\n | Administrative password recovery and factory reset<\/td>\n<\/tr>\n | \nRisk if Left in Place<\/strong><\/td>\n| None (Expected operational state)<\/td>\n | Router reboots with a blank configuration every time<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n<\/span>Modifying the Register in ROMMON for Password Recovery<\/span><\/h2>\nIf an administrator loses the enable password or is locked out of local AAA authentication, the configuration register must be changed from the ROM Monitor (ROMMON) to bypass NVRAM.<\/p>\n +-----------------------------------------------------------+\n| 1. Power cycle router & send Break signal during boot |\n+-----------------------------+-----------------------------+\n |\n v\n+-----------------------------------------------------------+\n| 2. At ROMMON prompt: confreg 0x2142 |\n| (or o\/r 0x2142 on legacy hardware) |\n+-----------------------------+-----------------------------+\n |\n v\n+-----------------------------------------------------------+\n| 3. Issue "reset" to reboot without loading NVRAM |\n+-----------------------------+-----------------------------+\n |\n v\n+-----------------------------------------------------------+\n| 4. Bypass Setup Dialog -> Enter Privileged EXEC Mode |\n+-----------------------------+-----------------------------+\n |\n v\n+-----------------------------------------------------------+\n| 5. copy startup-config running-config |\n| (Restores interface configs & prevents data loss) |\n+-----------------------------+-----------------------------+\n |\n v\n+-----------------------------------------------------------+\n| 6. Reset enable secret \/ admin user credentials |\n+-----------------------------+-----------------------------+\n |\n v\n+-----------------------------------------------------------+\n| 7. config-register 0x2102 |\n| copy running-config startup-config |\n+-----------------------------------------------------------+\n<\/code><\/pre>\n<\/span>Step 1: Establish a Physical Console Session<\/span><\/h3>\nConnect a rollover or RJ-45-to-USB console cable directly between your management computer and the router console port. Open a terminal emulator configured for
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