Showing results for 
Search instead for 
Did you mean: 
Join Customer Connection to register!
Pim Scheffers

3850 stack IOS upgrade


Is it possible to upgrade the IOS on a cisco 3850 stack in a non disruptive way?

Reloading 1 switch at a time?

Or do you need to reload the entire stack at once, like a 3750 stack?


Hello Luke,

I got two 3850, one with 3.6 and the other one is 3.2. To upgrade the 3.2 to 3.6 I don't have any .bin in 3.6 switch flash. Do you have any idea?

sure thing..


so you have a few options.  The easiest would be to enable the auto upgrade feature on the switch running 3.6.  Once its enabled, with the power off the 2nd switch (running 3.2) introduce it into the stack and power on.  Once it powers up it will join the stack and automagically update itself to 3.6.  It will take a couple automatic reloads, so be patient.  You also need to be sure that your 3.6 switch is running in "install mode."

Your other option is to go to and download the 3.6 .bin file.  you could then stage the switch - upgrade it before attaching to the stack.  Once its running 3.6 and in the same mode (Install/bundle) you can introduce it into the stack and it will join up as expected.

This guide will go over the details for you in more depth.





Thank you so much for your quick response. I did the 1st option, once it's reload When I do #show switch on 1st switch (3.6), 2nd switch status shows as Provisioned. Why is that?

And auto update will not support prior to 3.3.1, will this effect my step?

provisioning is the tool that we have built into the software to allow for a few options.  1. once we have a stack, a provision statement is set to allow for the easy "swap" of like hardware - i.e. if you needed to RMA a switch in the stack, you could do so without losing the config. 2. we can "provision" a switch before actually physically putting it in the stack - i.e. i could config ports and such like it was already a part of the stack and when I actually put it in the stack, it will assume that configuration.

As long as 3.6 is your main switch and running in "install mode" you can just enable the auto upgrade.  the command wouldn't work in reverse, meaning you could not enable it on the switch running 3.2.




Thank you Richard, now my switch is in Provisioned state, what should I do now to get it to Ready state?

Once you go through with the auto upgrade commands that i mentioned, it will join as expected.  No need to worry about the provision state at the moment.  Its purely cosmetic.

Ok cool, Switch one (3.6) is on production. Do I have to have down time to do it? will switch one restart?

nope, switch 1 (3.6) will not reload.  Just make sure you are in "install mode" but I'm guessing you are since you don't have a .bin file in flash.  Also remember to introduce the 2nd switch while its powered off, if you do while its powered on, then you will cause a stack merge and it will reload both of them.





I tried it and it didn't work for me. Any idea what I can do?


And I found this.


The purpose of the auto-upgrade feature is to allow a switch to be upgraded to a compatible software image, so that the switch can join the switch stack.

When a new switch attempts to join a switch stack, each stack member performs compatibility checks with itself and the new switch. Each stack member sends the results of the compatibility checks to the active switch, which uses the results to determine whether the switch can join the switch stack. If the software on the new switch is incompatible with the switch stack, the new switch enters version-mismatch (VM) mode.

If the auto-upgrade feature is enabled on the new switch, the active switch automatically upgrades the new switch with the same software image running on a compatible stack member. Auto-upgrade starts a few minutes after the mismatched software is detected before starting.


This means the new switch should not run prior 3.3.


Hello Richard,

Can I upgrade more than 4 switches to 03.06.03 version. I mean by using software install flash....  Saw in the past a restriction of 3. Correct me if I wrong.

Re: 3850 stack IOS upgrade

Im not sure where to copy the bin filebecause #show flash?
flash-1: flash-2: flash:

where do I need to copy the .bin file all 3 ??

(switch are stacked) first is : WS-C3850-48P

                           second :   WS-C3850-12S

Hello Richard,

Thanks for the detailed steps.

I have a stack of 2 switches but in " BUNDLE " mode. 

Can I use the same procedure you shared for " INSTALLED " mode, or there is a specific way of doing the upgrade. 


Thanks in advance for your quick response.



Hi Richard,


I have to upgrade a pair of 3850 running 16.3.x  to 16.4.x , Is there a way of upgrading it wihout interruption ? I mean one at a time ?



Dears, Just you have to follow bug fix for this version. 

I will proceed with this way. I hope it will work without any issues.