Stack Protocol Version Compatibility; Major Version Number Incompatibility Among Switches; Minor Version Number Incompatibility Among Switches - Cisco Catalyst 2960 Software Configuration Manual

Understanding Stacks

Stack Protocol Version Compatibility

The stack protocol version has a major version number and a minor version number (for example 1.4,
where 1 is the major version number and 4 is the minor version number).
Switches with the same Cisco IOS software version have the same stack protocol version. All features
function properly across the stack. These switches with the same software version as the master
immediately join the stack.
If an incompatibility exists, a system message describes the cause of the incompatibility on the specific
stack members. The master sends the message to all members.
For more information, see the
page 7-10

Major Version Number Incompatibility Among Switches

Switches with different Cisco IOS software versions likely have different stack protocol versions.
Switches with different major version numbers are incompatible and cannot exist in the same stack.

Minor Version Number Incompatibility Among Switches

Switches with the same major version number but with a different minor version number as the master
are considered partially compatible. When connected to a stack, a partially compatible switch enters
version-mismatch 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 version-mismatch mode with
the stack image or with a tar file image from the 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 stay off. Pressing the Mode button does
not change the LED mode.
Auto-advise and auto-copy identify which images are running by examining the info file and by
Note
searching the directory structure on the switch stack. If you download your image by using the copy tftp:
command instead of by using the archive download-sw privileged EXEC command, the correct
directory structure is not properly created. For more information about the info file, see the
Format of Images on a Server or Cisco.com" section on page
Catalyst 2960 and 2960-S Switches Software Configuration Guide, Release 15.0(1)SE
7-10
"Major Version Number Incompatibility Among Switches" procedure on
and the "Minor Version Number Incompatibility Among Switches" procedure on page
Chapter 7 Managing Switch Stacks
A-25.
7-10.
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