For what two reasons has the router loaded its IOS image from the location that is shown? (Choose two.)
A. Router1 has specific boot system commands that instruct it to load IOS from a TFTP server. B. Router1 is acting as a TFTP server for other routers. C. Router1 cannot locate a valid IOS image in flash memory. D. Router1 defaulted to ROMMON mode and loaded the IOS image from a TFTP server. E. Cisco routers will first attempt to load an image from TFTP for management purposes.
Correct Answers: A, C
Explanation:
The loading sequence of CISCO IOS is as follows:
Booting up the router and locating the Cisco IOS
1. POST (power on self-test)
2. Bootstrap code executed
3. Check Configuration Register value (NVRAM) which can be modified using the config-register command
0 = ROM Monitor mode
1 = ROM IOS
2 – 15 = startup-config in NVRAM
4. Startup-config filE. Check for boot system commands (NVRAM)
If boot system commands in startup-config
a. Run boot system commands in order they appear in startup-config to locate the IOS
b. [If boot system commands fail, use default fallback sequence to locate the IOS (Flash, TFTP, ROM)?]
If no boot system commands in startup-config use the default fallback sequence in locating the IOS:
a. Flash (sequential)
b. TFTP server (netboot)
c. ROM (partial IOS) or keep retrying TFTP depending upon router model
5. If IOS is loaded, but there is no startup-config file, the router will use the default fallback sequence for locating the IOS and then it will enter setup mode or the setup dialogue.
