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Cisco EtherSwitch Service Modules Feature Guide
Information About the Cisco EtherSwitch Service Modules
17
Cisco IOS Release 12.2(25)SEC
Switch Stack Software Compatibility Recommendations
All stack members must run the same Cisco IOS software version to ensure compatibility between stack
members.
We recommend the following:
• 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.
• If your switch stack must have Cisco EtherSwitch service modules or switches running IP base
images and IP services images, the Cisco EtherSwitch service module running the IP services image
should be the stack master. IP services image features become unavailable to all stack members if
the stack master is running the IP base image.
• At least two stack members should have the IP services image installed to ensure redundant support
of the IP services image features. The IP services image has precedence over the IP base image
during stack master election, assuming that the priority value of the stack members is the same. If
the stack master running the IP services image fails, the other stack member running the IP services
image becomes the stack master.
• When a Cisco EtherSwitch service module or switch running the IP services image joins a switch
stack running the IP base image of the same version, the IP services image Cisco EtherSwitch
service module or switch does not automatically become the stack master. If you want the
Cisco EtherSwitch service module running the IP services image to become the stack master, reset
the current stack master running the IP base image by using the reload slot stack-member-number
privileged EXEC command. The Cisco EtherSwitch service module running the IP services image
is elected the stack master, assuming its priority value is higher or the same as that of the other stack
members.
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.
Cisco EtherSwitch service modules or switches with the same Cisco IOS software version have the same
stack protocol version. Such modules are fully compatible, and all features function properly across the
switch stack. Cisco EtherSwitch service modules or switches with the same Cisco IOS software version
as the stack master join the switch stack immediately.
If an incompatibility exists, the incompatible stack members generate a system error message that
describes the cause of the incompatibility on the specific stack members. The stack master displays the
error message to all stack members.
These sections provide more detail about incompatibility in switch stacks:
• Major Incompatibility Between Cisco EtherSwitch Service Modules, page 17
• Minor Incompatibility Between Cisco EtherSwitch Service Modules, page 18
Major Incompatibility Between Cisco EtherSwitch Service Modules
Cisco EtherSwitch service modules or Catalyst 3750 switches with different Cisco IOS software
versions most likely have different stack protocol versions. Cisco EtherSwitch service modules or
Catalyst 3750 switches with different major stack protocol version numbers are incompatible and cannot
exist in the same switch stack.