If you are an administrator in a network somewhere you probably already know an important fact: Everything needs maintenance. At one point or another you have to upgrade something. In a perfect world, we would have consistent upgrade windows and periods of time we can take down a network for maintenance. If you have that, you are a lucky person. Looking for maintenance windows might fall into the same category as spotting a UFO. Often times, bugs or vulnerabilities bring forth these needed maintenance windows. In this case, I am upgrading a 3504 controller from version 8.5.151.0 to 8.5.161.6. The reason: CSCvs89410. This bug can corrupt images on 3600 and 3700 series access points.
I’ve found upgrades on Cisco wireless controllers are pretty simple. It might be a bit difficult finding that upgrade window. Whether it is one controller or an HA pair, I make sure to load the software on the controller and the access points in advance of the actual window. The window itself will only have a single activity of rebooting the controllers (and verification, cant forget that!).
Under the menu COMMANDS > Download File select the file type of Code. Here is where I uploaded version 8.5.161.6. You have options to add the file, such as directly from your machine (HTTP). I usually choose FTP since I store my file centrally.
Once the download process begins you will see status messages at the bottom of the page. If you have an secondary controller, part of this process is to also send it to that controller. This happens automatically.
Once the controller has downloaded the new software, you will be prompted to reboot the controllers. The message also gives you some helpful advice to “pre-download” the image to your access points.
The choice to make depends on whether you care about a longer outage. If you want a smaller outage window, pre-download the image on each access point. If I chose to reboot without the pre-download all of my access points would begin to download the image once the controller boots back up. This can take a while, especially if your controller is across a WAN somewhere. I normally pre-download the images. Under WIRELESS > Access Points > All APs select an AP to perform the pre-download on. Under that AP’s Advanced tab, scroll down to the AP Image Download section.
By this time, your controller will already have the new image ready to go. As shown on the image above, for each access point, click the Download Primary button. The AP will begin the download from the controller. If you check the AP status you will see an update that it is downloading the image. This is under WIRELESS > Access Points > All APs.
Continue repeating this process on each access point. Once the downloads are complete for all APs, you are ready to reboot the controller. Under COMMANDS > Reboot you will find options to reboot the controller or both if you have a secondary. I normally select the Both option to reboot both controllers during my outage window.
On a 3504 controller, the reboot feels like it is less than 5 minutes. Then all the APs begin to join with the image already up to date. I am not sure if it is some sort of bug, but I have noticed on occasion one or two APs that begin to download the image again. Either way, I find is the quickest way to minimize your outage and upgrade a Cisco 3504.
Zeros & Won 
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