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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02
Chapter 5 Managing Switch Stacks
Understanding Switch Stacks
For more information, see the “Stack Protocol Version Compatibility” section on page 5-11 and the
Cisco Software Activation and Compatibility Document on Cisco.com.
For information about mixed hardware and software stacks, see the Cisco Software Activation and
Compatibility Document on Cisco.com.
Stack Protocol Version Compatibility
Each software image includes a stack protocol version. 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). Both version numbers determine the level of compatibility among the stack
members. You can display the stack protocol version by using the show platform stack-manager all
privileged EXEC command.
Switches with the same Cisco IOS software version have the same stack protocol version. Such switches
are fully compatible, and all features function properly across the switch stack. Switches with the same
Cisco IOS software version as the stack master immediately join the switch stack.
If an incompatibility exists, the fully functional stack members generate a system message that describes
the cause of the incompatibility on the specific stack members. The stack master sends the message to
all stack members. For more information, see the “Major Version Number Incompatibility Among
Switches” procedure on page 5-11 and the “Minor Version Number Incompatibility Among Switches”
procedure on page 5-11.
For information about stack protocol version incompatibility in mixed hardware and software stacks, see
the Cisco Software Activation and Compatibility Document on Cisco.com.
Major Version Number Incompatibility Among Switches
Switches with different major Cisco IOS software versions usually have different stack protocol
versions. Switches with different major version numbers are incompatible and cannot exist in the same
switch stack.
For information about major version number incompatibility in mixed hardware and software stacks, see
the Cisco Software Activation and Compatibility Document on Cisco.com.
Minor Version Number Incompatibility Among 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. For more
information, see the “Understanding Auto-Upgrade and Auto-Advise” section on page 5-12.
To see if there are switches in VM mode, use the show switch user EXEC command. The port LEDs on
switches in VM mode stay off. Pressing the Mode button does not change the LED mode.
You can use the boot auto-download-sw global configuration command to specify a URL pathname for
the master switch to use to get an image in case of version mismatch.
For information about minor version number incompatibility in mixed hardware stacks, see the Cisco
Software Activation and Compatibility Document on Cisco.com.