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Extension practice

Configuration Register Practice Questions

Extension practice: boot behavior controlled by the configuration register.

Author-reviewed by LabFabric · 7 September 2026 · Report a content issue

One solved question, so you can see how these are marked

A router boots with show version reporting a configuration register value of 0x2142. What effect does this have?

The router ignores the contents of NVRAM and boots into setup mode without the saved configuration

Bit 6 of the register (0x2142) tells the router to skip reading the startup-config in NVRAM at boot, which is the classic setting used for password recovery and the cause of a router appearing blank after a reload.

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All 4 Configuration Register questions in this set

Answers and explanations appear when you work through the set above.

  1. Which value is the factory default configuration register that causes a router to boot normally and load its saved startup-config?

    • 0x2102
    • 0x2142
    • 0x2100
    • 0x0000

  2. After changing the configuration register back to 0x2102 with config-register 0x2102 and issuing reload, the router prompts 'System configuration has been modified. Save? [yes/no]'. Why should the answer be no in this scenario?

    • Answering yes is required to apply the new configuration register value
    • Answering yes would overwrite the existing startup-config in NVRAM with the current (blank) running-config, wiping the real configuration
    • Answering no prevents the configuration register from taking effect
    • The answer makes no difference in this scenario

  3. A router's configuration register is set to 0x2100, and show version confirms this. What is the correct way to fix it before the next reload?

    • Type config-register 0x2102 in global configuration mode while the router is running normally
    • Reload the router, then at the rommon prompt run confreg 0x2102 followed by reset
    • Edit the startup-config file directly to change the register value
    • Power cycle the device repeatedly until the register resets itself

  4. A router's startup-config was lost, but a valid configuration named live-config still exists in flash. Which sequence correctly restores it as the active configuration?

    • copy running-config flash, then reload
    • more flash:live-config to view it, then copy flash running-config specifying live-config as the source, then write memory
    • erase startup-config, then reload, then confreg 0x2102
    • copy flash:live-config startup-config only, with no further action needed