Quickstart:
1) Get the new IOS to the router
2) Verify the integrity of the new IOS binary
3) Change the boot statements to ensure that the correct IOS loads after restart
4) Save configuration changes
5) Reload the device and verify that the correct IOS has loaded
Why change IOS versions:
The most frequent reasons that one would change the IOS on a router are:
- New version has new features
- New version fixes or avoids triggering a bug
- Security patching/compliance (ex PCI compliance)
Potential Caveats:
Usually these would only affect older routers but the main caveats would be ensuring there is enough system memory (RAM) and also flash to store the new IOS.
Step 1: Get the new IOS to the router.
If you are onsite then often the simplest way to get the new IOS to the router is to copy the IOS to a flash card, or on newer ISR G2s, USB thumb drive.
Otherwise you would copy the file to the router using TFTP, FTP, etc. Detailed instructions for this step are out of scope but an example would be:
copy ftp: flash:
(Follow the prompts for server IP and file name.)
Step 2: Verify the integrity of the new IOS binary
The next step we take is to verify that the IOS was not corrupted during transit or copying.
verify flash:c2800nm-advsecurityk9-mz.150-1.M8.bin
Success will show that the calculated MD5 hash is the same as the embedded hash.
Step 3: Change the boot statements to ensure that the correct IOS loads after restart
We need to remove the old boot statement(s) and add the new one. (There are other ways to select which IOS to run but this is the simplest method.)
a. examine the current boot statement(s)
show run | include boot
boot-start-marker
boot system flash:c2800nm-advsecurityk9-mz.12.4-15.T3.bin
boot-end-marker
b. remove the old boot statement (Output in step a)
config t
no boot system flash:c2800nm-advsecurityk9-mz.12.4-15.T3.bin
c. add the new boot statement (this will include the file name of the new binary)
boot system flash:c2800nm-advsecurityk9-mz.15.0-1-M8.bin
Step 4: Save configuration changes
While still in configuration mode from before:
end
write memory
show start | include boot
boot-start-marker
boot system flash:c2800nm-advsecurityk9-mz.15.0-1-M8.bin
boot-end-marker
To recap all of the commands (in this example) would then be:
show run | include boot
config t
no boot system flash:c2800nm-advsecurityk9-mz.12.4-15.T3.bin
boot system flash:c2800nm-advsecurityk9-mz.15.0-1-M8.bin
end
write memory
show start | include boot
Step 5: Reload the device and verify that the correct IOS has loaded
For normal ISR's the only way to change the IOS is to reload the device. (ISSU, In-Service Software Upgrade, is not currently supported.)
After the device has reloaded please do a "show version" and confirm that the router is now running the correct version of IOS.
Then you are done.
