Software compatibility between the stack members is determined by the Stack Protocol Version number. To view the stack protocol version of your switch stack, you can issue the show platform stack manager all 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. 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 switch stack. Switches with the same major version number but with a different minor version number as the stack master 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 functional 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 auto-upgrade occurs if the software release that runs on the stack master is compatible with the switch in VM mode and the tar file of the current image is available with any of the stack members. If tar file of the current image is not available, the auto-advise feature will recommend that a compatible image be downloaded with the required commands.
Note: If the auto upgrade does not work on the switch that shows the version mismatch error, use TFTP to manually upgrade the switch. The stack member number of Switch-A will change since it conflicts with Switch-B. Switch-A will choose the lowest available stack number, which in this case, is number "2". When these two switch stacks are merged together, the election for stack master occurs; let us consider that Switch-B wins the election.
Switch-C and Switch-D will reload themselves and join the stack with new stack member numbers of "3" and "4" respectively. Note: Make sure the switch that you add into the stack has the same IOS version as the switches in the stack. Refer to to upgrade the IOS in a catalyst switch. Note: This step is optional, but it will make sure that the switch has fewer chances to become a stackmaster in the future.
Make sure that the stack is fully connected so that, when you connect the new switch, the stack will be at least in half connectivity and does not partition. After the new switch comes up, issue the command show switch to verify stack membership.
Note: Make sure the switch you add into the stack has the same IOS version as the switches in the stack. Issue the show switch command. Change the priority value of the switch to be added to a value greater than the highest priority of the stack. In the illustration, the priority value has to be a value of more than "5. Make sure that the stack is fully connected so that, when you connect the new switch, the stack will be at least in half connectivity, and do not partition.
The election for the stack master occurs, and the new switch will be elected as the master since it has the highest priority value. The members of the previous stack will reboot themselves to join the new stack. After all the members come up, issue the command show switch to verify stack membership. Make sure that the stack is fully connected so that, when you remove the member, the stack will be at least in half connectivity, and do not partition. If the member was the stack master, the stack master election will occur, otherwise no election will occur.
When you add a provisioned switch to the switch stack, the stack applies either the provisioned configuration or the default configuration to it. If you add a provisioned switch that is a different type than specified in the provisioned configuration to a powered-down switch stack and then apply power, the switch stack rejects the now incorrect switch stack-member-number provision type global configuration command in the startup configuration file.
Within stack initialization, the nondefault interface configuration information in the startup configuration file for the provisioned interfaces potentially of the wrong type are executed. Dependent upon how different the actual switch type is from the previously provisioned switch type, some commands are rejected, and some commands are accepted. You can use the offline configuration feature to provision to supply a configuration to a new switch before it joins the switch stack.
In advance, you can configure the stack member number, switch type, and interfaces associated with a switch that are not currently part of the stack. The configuration that you create on the switch stack is called the provisioned configuration. The switch that is added to the switch stack and that receives this configuration is called the provisioned switch.
You manually create the provisioned configuration through the switch stack-member-number provision type global configuration command. When a is added to a stack, the stack master determines if there are any provisioned switches that are not currently live in the stack.
If there is a switch configuration provisioned that matches the number assigned to the new switch, the new switch assumes that number in the stack, and that configuration. If the new switch has the same number as an existing live switch member in the stack, the new switch assumes the lowest provisioned available number in the stack, and any config in the master switch is applied to the newly provisioned switches.
If there are no more provisioned switches in the stack, the newly inserted switch will retain its existing number, if this number does not already exist in the stack. If the number configured on the switch exists in the stack, the switch will assume the lowest available number. The configuration of ports on this switch will be set to defaults. In order to change the numbering of the switch and all of its ports back to 1, it is necessary to configure this manually, with the command: Switch renumber It is possible to renumber a switch while it is in a stack, but you cannot change it to a number that is currently active in the stack.
When a switch is removed from a stack, it also retains all the provisioned information for the former members of the stack- it is necessary to unprovision the former stack members: No switch provision With these parameters in mind, the following best practices should be kept in mind: When building a stack: Boot the switch you desire to be the stack master, and configure the switch priority as 15 as the higher the priority number wins the master election.
Switch 1 priority 15 After removing a switch from a stack: Write erase Switch renumber 1 reload Active Console Ports: All console ports in a are active. Working with the. This is very similar to the process in place with other cisco devices. There are certain parameters available to force a reload after the successful upgrade, as well as either delete the old image or keep it until a successful upgrade has been completed.
This is approximately a 10 minute process, largely done without much output to the console- be patient. Also, turn off spanning tree to speed up bringing up the link. The master switch in a stack is the one with the highest priority. To make sure that this new switch becomes the master, make its priority the same or higher than the failed switch.
Set the priority like this:. Power down the entire stack and disconnect the failed master switch. The entire stack will lose its configuration when the master switch is replaced. This is okay, because we regularly back up our configs, right?
Make sure to note the pattern of how the cables plug in so that you can plug them in to the new switch in the same way. Connect the new master switch and power up the stack. Connect everything up. Make sure to use a screwdriver to tighten up the stacking cables, as they have pretty shallow receptacles.
It shouldn't be an issue though, just make sure you have your new switch powered off as you connect all the stacking cables. We did that a few years back. Racked the second switch and plugged the cable between them. It is treated as one large switch with the same ip. I am not sure if we shutdown the first switch or not. Probably did. I personally give 30 seconds between powering them up myself.
LenMC pointed out an important caveat. When adding a new to an existing stack, it must be running a very similar if not the exact same version and feature set of code as the existing stack. As a matter of best practice, I always change the IOS on the new switch before adding it to the stack. Also, just to be on the safe side I set the switch priority on the new switch manually before adding it to the stack.
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