If you erase the contents of NVRAM (startup configuration) on a Cisco router and then reboot it, which mode will the router enter on startup?

Introduction / Context:
This question tests your understanding of how a Cisco router behaves when there is no startup configuration stored in NVRAM. In real networks and in Cisco certification exams, you must know what happens after you erase the startup configuration and reload the router, because this is a common step when preparing devices for reuse or lab work.

Given Data / Assumptions:

• The router originally had a configuration saved in NVRAM as the startup configuration.
• The contents of NVRAM have been erased using a command such as erase startup-config or write erase.
• The router is then reloaded with a normal IOS image available in flash.
• No configuration file is present for the router to load at boot time.

Concept / Approach:
During the boot process, a Cisco router loads the IOS image from flash and then attempts to load the startup configuration from NVRAM into RAM as the running configuration. If NVRAM is empty, the router cannot find a startup configuration. In that case, IOS enters a special interactive Setup mode, also called the initial configuration dialog, which guides the administrator through a series of questions to create a basic configuration. The command prompt you see first is user EXEC, but the characteristic behaviour is the automatic start of Setup mode.

Step-by-Step Solution:
Step 1: The router powers on and runs the bootstrap code stored in ROM.Step 2: The bootstrap code locates and loads the IOS image from flash into memory.Step 3: IOS attempts to load the startup configuration from NVRAM into RAM as running-config.Step 4: Because NVRAM is empty, IOS detects that no startup configuration exists.Step 5: IOS presents the initial configuration dialog, commonly called Setup mode, asking whether you want to enter basic configuration commands.

Verification / Alternative check:
In a lab, if you erase the startup configuration and reload, you will see a prompt similar to: Would you like to enter the initial configuration dialog? This confirms that the router has entered Setup mode and that NVRAM was empty at boot time.

Why Other Options Are Wrong:
Option A mentions user EXEC mode, which appears briefly, but without highlighting Setup mode it misses the main behaviour tested by this question.Option B is incorrect because the router does not drop directly into privileged EXEC mode with no configuration.Option D is wrong because ROM monitor mode is used when there is a problem with the IOS image, not simply because the configuration is missing.Option E is incorrect because the router does not automatically place you into global configuration mode with interfaces enabled.

Common Pitfalls:
Students sometimes confuse Setup mode with normal user or privileged EXEC modes. Setup mode is a guided configuration dialog that appears only when no startup configuration is present. Knowing this difference is important when you prepare routers for labs or when you inherit used equipment that must be wiped and reconfigured.

Final Answer:
The router will enter Setup mode (initial configuration dialog) used to create a new basic configuration after you erase NVRAM and reboot.