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.
The switch with the higher version of software is made the active switch and all other switches that are to be upgraded are
booted simultaneously. If you have new switches to add to the stack, first power them off, add them to the stack and then
boot them simultaneously. You cannot add more members to a stack when an auto-upgrade is going on in the stack. You can add
new members only after the on-going auto-upgrade process is completed.
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 stack, 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 existing switch stack, the active stack 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.
You can perform auto-upgrade on the newly added member of a stack only after the existing members of the stack are already
Auto-upgrade is disabled by default.
Note the following limitations before starting an auto-upgrade:
Do not perform an auto-upgrade in bundle mode.
Do not perform an auto-upgrade in half-ring stack.
Do not perform stack merge of two active switches that have different version of images.
Do not perform staggered boot of the switches to be upgraded.
an auto-copy process and an auto-extract process.
automatically copies the software image running on any stack member to the new
switch to automatically upgrade it. Auto-copy occurs if auto-upgrade is
enabled, if there is enough flash memory in the new switch, and if the software
image running on the switch stack is suitable for the new switch.
A switch in VM mode might not run all released software. For example, new switch hardware is not recognized in earlier versions
Automatic extraction (auto-extract) occurs when the auto-upgrade process cannot find the appropriate software in the stack
to copy to the new switch. In that case, the auto-extract process searches all switches in the stack for the bin file needed
to upgrade the switch stack or the new switch. The bin file can be in any flash file system in the switch stack or in the
new switch. If a bin file suitable for the new switch is found on a stack member, the process extracts the file and automatically
upgrades the new switch.
The auto-upgrade feature is not available in bundle mode. The switch stack must be running in installed mode. If the switch
stack is in bundle mode, use the software expand privileged EXEC command to change to installed mode.
You can enable auto-upgrade by using the software auto-upgrade enable global configuration command on the new switch. You can check the status of auto-upgrade by using the show running-config privileged EXEC command and by checking the Auto upgrade line in the display.
You can configure auto-upgrade to upgrade the new switch with a specific software bundle by using the software auto-upgrade source url global configuration command. If the software bundle is invalid, the new switch is upgraded with the same software image
running on a compatible stack member.
When the auto-upgrade process is complete, the new switch reloads and joins the stack as a fully functioning member. If you
have both stack cables connected during the reload, network downtime does not occur because the switch stack operates on two
For more information about upgrading a switch running incompatible software see the Cisco IOS File System, Configuration Files, and Bundle Files Appendix, Cisco IOS XE Release 3SE (Catalyst 3850 Switches).