Cisco 1841 IOS upgrade

Posted on 2012-08-27
Last Modified: 2012-09-17

I have to upgrade the IOS image of the Cisco 1841 IOS router with a new IOS image.
Please if someone let me know the steps of how to do it.

I have a disk which has around 5 IOS images. So how to run which IOS image etc.

Please someone can brief me about the steps of IOS upgarde with all details of the each steps.

I have conncted the console on the Cisco 1841 router.
Question by:network-guru
    LVL 25

    Expert Comment

    LVL 17

    Accepted Solution

    If you can't run SDM (it's sometimes a bit flaky) you can do it on the console ... I assume you can get to the console either via serial line, or by telnet/ssh. Also assuming the router has a working network connection to your LAN.
    Depending on the version of IOS on the box right now, you can use either TFTP (always works) or ftp/http to get the newer IOS onto the router.
    First make sure you're putting an IOS on the router that has all the features you're already using, which can be done by comparing the file name of the image. Do a "show version" to see which IOS is currently being used (alternatively, do "show flash:", chances are there's only one image currently on the router). Chose an IOS whose name is the same you already have, apart from the version ... (caveat: the name alone in some cases may not be enough, as e.g. the 12.4T train has features the regular 12.4 does not have - albeit they may not be used). You may just want to post the name of the current IOS, as well as the ones you have available ... for a decision, a sanitized version of the config may also be required ...
    Once you have selected the IOS, you need to transfer it to the router. Next hurdle: Is there enough space to store the additional IOS? Again, check the output of the "show flash" command, which states how much space is free in the flash. Compare it to the IOS you want to install. If it's too large, you will need to delete unnecessary files (choosing which are may require some knowledge of Cisco routers), worst case you will need to delete the old image and install the new - if something goes wrong in between, you need to do some more serious hacking to get the image back on the router (serial X-Modem upload in the boot loader).
    Assuming you have enough space, make sure you have a TFTP server available (see Solarwinds TFTP e.g.), store the image there, and copy it with "copy tftp flash", answering the question about the server (enter the IP of the TFTP server), the filename (use the image file name) and the destination (just press enter), and it should copy the image to flash. Once done, configure the new image to be used. First check whether there is a line "boot image flash..." or similar ... if so, delete it ("no boot image flash ...") and put in the new image name instead. For safety, I'd add the old line after that again. That way, if anything is wrong with the new image, the router will fail loading it and continue booting with the old image, leaving you with a working, albeit not updated router.
    Also, I'd recommend copying the working config to flash or the TFTP server ("copy run flash:config-backup"). If the new image is missing some features, and you update the config with the new image running, you may otherwise lose the not supported parts of the config ...

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