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IOS upgrade by deleting existing one

Dear Team,

I have a question out of my curiocity. even though I have done this before in working environment I just want to know how it works..

Scenario:

1. Inorder to upgrade the IOS, If I deleted the existing IOS from Router flash/disk due to memory constraints.

My Question is:

1. During router bootup, Does the whole IOS copied to RAM to perform all the functions an IOS can do? --- assume so

if not if the IOS is deleted, if you configure something new on router which might need a special process of IOS to perform this job but unfortunately IOS is not on disk. sure this is not the case, otherwise I wouldnt able to do it...

or 2. whole IOS copied/uncompressed to NVRAM during router bootup and the IOS functions(programs) available in NVRAM these will be loaded to RAM(dynamic) on demand to perform a specific task by main CPU.

I am just comparing the IOS bootup/working process with normal OS(Linux/windows)... I know its not fair....

Please clear my doubt/question.

Thanks in advance

Sanjeev

1 REPLY
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Re: IOS upgrade by deleting existing one

sanjeevreddyallala wrote:

Dear Team,

I have a question out of my curiocity. even though I have done this before in working environment I just want to know how it works..

Scenario:

1. Inorder to upgrade the IOS, If I deleted the existing IOS from Router flash/disk due to memory constraints.

My Question is:

1. During router bootup, Does the whole IOS copied to RAM to perform all the functions an IOS can do? --- assume so

if not if the IOS is deleted, if you configure something new on router which might need a special process of IOS to perform this job but unfortunately IOS is not on disk. sure this is not the case, otherwise I wouldnt able to do it...

or 2. whole IOS copied/uncompressed to NVRAM during router bootup and the IOS functions(programs) available in NVRAM these will be loaded to RAM(dynamic) on demand to perform a specific task by main CPU.

I am just comparing the IOS bootup/working process with normal OS(Linux/windows)... I know its not fair....

Please clear my doubt/question.

Thanks in advance

Sanjeev

Sanjeev

The answer is 1) for the reasons you have stated. NVRAM is used to store information that does not get lost across reloads so there is no reason you would need to store parts of the IOS functionality in NVRAM.

Besides as NVRAM keeps it's information across reboots then in theory you could delete the IOS from flash and reload and it would all work but clearly it doesn't.

Jon

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