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For example, there's 4400 series router may have modules installed, such as in this bottom example or

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may not have modules installed.

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So when the router boots up, it's got to determine what interfaces it has inserted, what modules are

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available, how much RAM is available, and various other components.

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You could even install a UCS server into a router today.

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So when the rubber boots up, it needs to determine what's physically installed and available on the

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router.

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So the power on self-test will test the basic functionality of the router hardware to determine whether

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it's working, determine whether it's supported, and determine which components are present.

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As an example, you may have mistakenly inserted a voice interface card into a WAN interface card slot.

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Voice interface cards or

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VICs may need to be inserted into specific modules and you may have inserted the wrong card into the

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wrong module on a router.

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So it needs to do this power and self-test to determine what's installed and whether things are installed

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correctly and working correctly.

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ROM Monitor includes a low-level operating system that is used for troubleshooting, password recovery and

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testing.

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This is different to the standard operating system and doesn't support routing.

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You could use ROM Monitor as an example to download a router operating system if there's none available

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on the router

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or you could use ROM Monitor to do a password recovery, which I'll demonstrate in this course.