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 existing switch stack, the
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.
Auto-upgrade is disabled by default.
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 of software.
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 rings.
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).