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New Member

ios upgrade

I use a 3845 cisco router and need to upgrade an ios but there is not enough space to accomodate the latest version with the one that is currently running. My question is can I erase the current one befor updating with the latest? would it boot after I have deleted the the current one?


Re: ios upgrade

before delete the old ios, take a copy from it by tftp.

then you can delete the old ios, and DO NOT POWER OFF the rtr.

you must download on it the new soft. then make sure if you need to change some commads that specify the name of ios to use.

then you can reload the rtr.


1-some times you need to use the command squeeze after delete to use the old space.

2-in case of boot failure, reload the old soft from rommon

Super Bronze

Re: ios upgrade

Oussama summarizes the procedure. Router should not automatically reload with an ordinary flash load.

When changing IOS, you should also check whether boot is defined in config or whether there are any other IOS versions on same or different flashes. This to insure if there's more than one IOS on the system, system boots the one you desire.

BTW: The 3845 might supports some USB devices. Might also even support booting from them. If so, its another possible option for storing an IOS image on the router.

New Member

Re: ios upgrade

If you are upgrading it remotely, you can

enter these commands once the ios is deleted:

1. To Boot over the network(from a device thats near to the router)

#boot system tftp ios_image ip address

So that if the router gets switched off for any reason, it will still boot but slowly.

2. Once the new image has been downloaded, you Have to remove the above command, before reloading. Do not forget to remove this !


Cisco Employee

Re: ios upgrade


The command 'boot system tftp ios_image ip address' would help boot the router from the IOS on a tftp server only if there is a working IOS image as the first file in the flash. You can not boot the router from an IOS on the tftp server without having an IOS image in the flash. This is because, the router's interface would not come up and have an IP address on it without an IOS, thus stopping all communication.

You can definitely copy an IOS from a tftp server when the router is in ROMMON using TFTPDNLD procedure, but that's different.

Lawrence, in response to you query, as has been already said - yes, you can delete the file even before you copy the new one. However, you need to ensure that the router is not rebooted till the time the new IOS is not copied. Even if its rebooted accidentally, there are ways to recover it.

Once the new file is copied, issue - show flash: to see if the new image is the first file (which it would be if you erase the flash and not just delete a specific file). If yes, you can safely power cycle the router. If its not the first file then include a boot statement in your config.


conf t

boot system flash:


write mem


Do keep in mind that the file_name is case sensitive.



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