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TOPIC: LOADING THE IOS

LOADING THE IOS 7 years 2 weeks ago #31902

  • Losh
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Hi people, I,ve just completed my ccna 4 and some questions realy had my head spinning e.g

If a router is unable to find a suitable IOS to load into RAM, in what mode does the boot process end?
-setup mode
-user mode
-rommon mode
-priviledge mode
~ Networking :- Just when u think its starting to make sense......... ~
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Re: LOADING THE IOS 7 years 2 weeks ago #31903

Router boot sequence is:

FLASH
TFTP
RXBoot
ROMMON

IE, the router goes through POST, then looks at the Flash memory first. If no IOS is found it looks for a TFTP server. If no TFTP server is found it goes to RXBoot, which loads a "cut down" version of the IOS from ROM which has some functionality. If that doesn't work, then you get ROMMON which has even less functionality, but gives you enough to work with to recover the IOS from a back-up somewhere, or by using a nearby router to act as a server so you can copy it's IOS to the dead router. This requires a bit of prep though. Nothing too hard, but a few lines of config need to be gone through and some notes made for things like IP adresses etc.
You can force the router to boot from a specific location by alltering the Configuration Register number at global config.

By far the best resource for these sorts of situations, ie configs that you could do with knowing but don't practice an awful lot, is a book called the CCNA Portable Command Guide. I keep one in my laptop bag at all times for those times when I want to TFTP something, or recover an IOS or password recover a switch... etc...
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Re: LOADING THE IOS 7 years 2 weeks ago #31914

  • S0lo
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Router boot sequence is:

FLASH
TFTP
RXBoot
ROMMON

Losh, so the answer to your question should be rommon mode. Since thats the last resort when the router can't find an IOS.

By the way, you could alter that sequence using the boot system command while setting the configuration register to any value from 0xnnn2 to 0xnnnF as broadcaststorm noted.
Studying CCNP...

Ammar Muqaddas
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www.firewall.cx
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Re: LOADING THE IOS 7 years 2 weeks ago #31932

  • Losh
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Thanx alot broadcastorm and solo. Thats some good answers you got there.
~ Networking :- Just when u think its starting to make sense......... ~
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CCNA, CCNP, CCNA Security, JNCIA, APDS, CISA
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