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Catalyst 3750 Switch Software Configuration Guide
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Chapter 5 Managing Switch Stacks
Understanding Switch Stacks
To ensure complete compatibility between stack members, use the information in this section and in the
“Hardware Compatibility in Switch Stacks” section on page 5-10.
Compatibility Recommendations
All stack members must run the same Cisco IOS software version to ensure compatibility between stack
members.
Follow these recommendations:
• The Cisco IOS software version on all stack members, including the stack master, should be the
same. This helps ensure full compatibility in the stack protocol version among the stack members.
For example, all stack members should have the EMI Cisco IOS Release 12.1(14)EA1 installed.
• If your switch stack must have switches running SMI and EMI software, the switch running the EMI
software should be the stack master. EMI features become unavailable to all stack members if the
stack master is running the SMI software.
• At least two stack members should have the EMI software installed to ensure redundant support of
the EMI features. The EMI has precedence over the SMI during stack master election, assuming that
the priority value of the stack members are the same. If the EMI stack master fails, the other stack
member running the EMI software becomes the stack master.
• When a switch running the EMI joins a switch stack running the SMI of the same version, the EMI
switch does not automatically become the stack master. If you want the EMI switch to become the
stack master, reset the current SMI stack master by using the reload slot stack-member-number
privileged EXEC command. The EMI switch is elected the stack master, assuming its priority value
is higher or the same as the other stack members.
Incompatible Software and Stack Member Image Upgrades
You can upgrade a switch that has an incompatible software image by using the archive copy-sw
privileged EXEC command. It copies the software image from an existing stack member to the one with
incompatible software. That switch automatically reloads and joins the stack as a fully functioning
member. For more information, see the “Copying an Image File from One Stack Member to Another”
section on page B-34.
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. 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 incompatible stack members generate a system message that describes
the cause of the incompatibility on the specific stack members. The stack master displays the message
to all stack members.
These sections provide more detail about incompatibility in switch stacks:
• Major Incompatibility Between Switches, page 5-12
• Minor Incompatibility Between Switches, page 5-12
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