Cisco Catalyst 2960 Series, Configuration Manual

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Minor Stack Protocol Version Number Incompatibility Among Stack-Capable Switches
Switches with the same major version number but with a different minor version number are considered
partially compatible. When connected to a switch stack, a partially compatible switch enters version-mismatch
(VM) mode and cannot join the stack as a fully functioning member. The software detects the mismatched
software and tries to upgrade (or downgrade) the switch in VM mode with the switch stack image or with a
tar file image from the switch stack flash memory. The software uses the automatic upgrade (auto-upgrade)
and the automatic advise (auto-advise) features.
The port LEDs on switches in version-mismatch mode will also remain off. Pressing the Mode button does
not change the LED mode.
Auto-Upgrade
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
switchstack master, 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 switchstack master 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.
By default, auto-upgrade is enabled (the boot auto-copy-sw global configuration command is enabled). You
can disable auto-upgrade by using the no boot auto-copy-sw global configuration command on the stack
master. You can check the status of auto-upgrade by using the show boot privileged EXEC command and by
checking the Auto upgrade line in the display.
Auto-upgrade includes an auto-copy process and an auto-extract process.
• Auto-copy 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.
Note
• 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 tar file needed to upgrade the switch stack or the new switch. The tar file can be in
any flash file system in the switch stack or in the new switch. If a tar 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 (auto-copy and auto-extract) processes start a few minutes after the mismatched software
is detected.
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.
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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Information About Switch Stacks