There are a number of scenarios when you would need to introduce a new switch into an existing stack of 3850 switches. One particular example is when a new switch is purchased to expand the number of usable ports in the stack. To successfully add a new switch to a stack, you will need to ensure that the same software version is running on the new switch. Prior to IOS-XE release 3.3.1, the only way to ensure the versions matched was to stage the new switch prior to introducing it into the stack.
The 3850, includes a feature called “Auto-Upgrade” which might be familiar if you are migrating from the 3750 series platform. The goal of this feature is to ensure that any newly added switch will automatically be provisioned by the stack members with the running IOS-XE version. One caveat to note however is that prior to 3.3.1, this feature did not work (Tracked by defect CSCui69999), and so you must ensure that your existing stack is running at least 3.3.1 in INSTALL mode.
** Auto-upgrade is disabled by default.
** Auto-upgrade is not available in bundle mode.
To utilize the “Auto-Upgrade” feature, you simply need to add the command “software auto-upgrade enable” in the running configuration of the existing stack. This will ensure that any newly added stack members will automatically be upgraded.
Once the switch is stacked and booted up, you will see a clear indication that there is a mismatch in versions and the new member will not fully join the stack. If you watch the syslog as the switch is trying to join, you will notice the “auto advise” feature will alert you that the newly added switch is running a different software version and mode (INSTALL & BUNDLE explained here). For this example, my new switch is running IOS-XE version 3.2.2 in BUNDLE mode.
%STACKMGR-1-STACK_LINK_CHANGE: STANDBY: 1 stack-mgr: Stack port 2 on switch 1 is up (3850-Stack-1)
%STACKMGR-1-STACK_LINK_CHANGE: 2 stack-mgr: Stack port 1 on switch 2 is up
%STACKMGR-6-SWITCH_ADDED: 2 stack-mgr: Switch 3 has been added to the stack.
%STACKMGR-6-SWITCH_ADDED: STANDBY:1 stack-mgr: Switch 3 has been added to the stack. (3850-Stack-1)
%INSTALLER-6-AUTO_ADVISE_SW_INITIATED: 2 installer: Auto advise initiated for switch 3
%INSTALLER-6-AUTO_ADVISE_SW: 2 installer: Switch 3 running bundled software has been added
%INSTALLER-6-AUTO_ADVISE_SW: 2 installer: to the stack that is running installed software.
%INSTALLER-6-AUTO_ADVISE_SW: 2 installer: The 'software auto-upgrade' command can be used to
%INSTALLER-6-AUTO_ADVISE_SW: 2 installer: convert switch 3 to the installed running mode by
%INSTALLER-6-AUTO_ADVISE_SW: 2 installer: installing its running software.
Once the newly joined member is fully booted, you can see that a mismatch has been detected.
Switch/Stack Mac Address : 0c27.24cf.ab80 - Local Mac Address
In global configuration mode, type the command “software auto-upgrade enable.” This will enable the feature for any new switches that join the stack.
3850-Stack(config)#software auto-upgrade enable
You will now have to reload the newly added switch only, a full stack reload is not necessary. In my case, the newly added switch is “switch 3” so I simply type “reload slot 3.” Remember that “slot” designates the switch in the stack (slot 1 = switch 1)
3850-Stack#reload slot 3
Proceed with reload? [confirm]
%STACKMGR-1-RELOAD_REQUEST: 1 stack-mgr: Received reload request for switch 3, reason Reload Slot Command
%STACKMGR-1-STACK_LINK_CHANGE: 1 stack-mgr: Stack port 2 on switch 1 is down
%STACKMGR-6-SWITCH_REMOVED: 1 stack-mgr: Switch 3 has been removed from the stack.
%STACKMGR-1-STACK_LINK_CHANGE: STANDBY:2 stack-mgr: Stack port 1 on switch 2 is down (3850-Stack-2)
Starting SWITCH-DELETE sequence, switch 3
SWITCH-DELETE sequence complete, switch 3
%STACKMGR-6-SWITCH_REMOVED: STANDBY:2 stack-mgr: Switch 3 has been removed from the stack. (3850-Stack-2)
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