What is best practice when it comes to upgrading Cisco IOS? I have a production router that needs to be upgraded from version 3 to 16 but since it is my first time, I am worried that I may end up breaking it. Is it generally safe to do the upgrade?
It is safe practice to do but definitely you should consider to do it in the maintenance window. Take appropriate downtime ( i would suggest 2 hours atleast, since it is your 1st time. Although it may take less than 10 minutes for the upgrade. ) or schedule anything.
As part of the upgrade, you have to copy the Image to the Router either using FTP or TFTP. I would suggest you to use FTP as it is faster and reliable. Once copied, verify the MD5 hash of the copied file in the Router cli and compare it with the MD5 hash mentioned in the Cisco site where you download the software.
In below example, hasg if this image c7301-jk9-mz.124-10.bin = ad9f9c902fa34b90de8365c3a5039a5b
verify /md5 disk0:c7301-jk9s-mz.124-10.bin .....<output truncated>.....Done! verify /md5 (disk0:c7301-jk9s-mz.124-10.bin) = ad9f9c902fa34b90de8365c3a5039a5b router#
verify is it same mentioned in the Cisco Site next to the file.
Once above is done, we will be sure that file is properly downloaded and copied to the Router and integrity is not damaged. After that, during the maintenance window, you will use the "boot system flash:................" in the cli to change it from old image to new, save and reload :)
I have a production router that needs to be upgraded from version 3 to 16 but since it is my first time
Read the Release Notes very, very carefully.
If you've never done this before, the Release Notes will also provide detailed instruction (Install Mode) about how to do the upgrade correctly.