Switch Stack

All stack members must run the same Cisco IOS software image to ensure compatibility among stack members.
From the stack master, you configure:
  • System-level (global) features that apply to all stack members
  • Interface-level features for each stack member
The stack master contains the saved and running configuration files for the switch stack. The configuration files include the system-level settings for the switch stack and the interface-level settings for each stack member. Each stack member has a current copy of these files for back-up purposes.

Switch Stack Membership
A standalone switch is a switch stack with one stack member that also operates as the stack master.
Adding powered-on switches (merging) causes the stack masters of the merging switch stacks to elect a stack master from among themselves. The reelected stack master retains its role and configuration as do its stack members.
Make sure that you power off the switches that you add to or remove from the switch stack.
After adding or removing stack members, make sure that the switch stack is operating at full bandwidth(40 Gb/s). Press the Mode button on a stack member until the Stack mode LED is on. The last two right port LEDs on all switches in the stack should be green.

A new, out-of-the-box switch (one that has not joined a switch stack or has not been manually assigned a stack member number) ships with a default stack member number of 1. When it joins a switch stack, its default stack member number changes to the lowest available member number in the stack.

A higher priority value for a stack member increases the probability of it being elected stack master and retaining its stack member number. The priority value can be 1 to 15. The default priority value is 1. Use "show switch". We recommend assigning the highest priority value to the switch that you prefer to be the stack master. To change the priority value for a stack member, use the switch stack-member-number priority new priority-value global configuration command. The new priority value takes effect immediately but does not affect the current stack master.

The stack master is elected or reelected based on one of these factors and in the order listed:
1. The switch that is currently the stack master.
2. The switch with the highest stack member priority value.
3. The switch that has the configuration file.
4. The switch with the lowest MAC address.
After a new stack master is elected and the previous stack master becomes available, the previous stack master does not resume its role as stack master.

Switch Stack Configuration Files
The stack master has the saved and running configuration files for the switch stack. All stack members periodically receive synchronized copies of the configuration files from the stack master.

A new, out-of-box switch joining a switch stack uses the system-level settings of that switch stack. If a switch is moved to a different switch stack, that switch loses its saved configuration file and uses the system-level configuration of the new switch stack.
  • If an interface-specific configuration does not exist for that member number, the stack member uses its default interface-specific configuration.
  • If an interface-specific configuration exists for that member number, the stack member uses the interface-specific configuration associated with that member number.
If you replace a failed member with an identical model, the replacement member automatically uses the same interface-specific configuration as the failed switch. must have the same stack member number as the failed switch.

Offline configuration to Provision a Stack Member
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 you configure the interfaces associated with a provisioned switch (for example, as part of a VLAN), the switch stack accepts the configuration, and the information appears in the running configuration. The interface associated with the provisioned switch does not appear in the display of the specific feature(show vlan). The switch stack retains the provisioned configuration in the running configuration whether or not the provisioned switch is part of the stack.

If you remove a provisioned switch from the switch stack, the configuration associated with the removed stack member remains in the running configuration as provisioned information. (use the no switch stack-member-number provision global configuration command.) You can display the stack protocol version by using the show platform stack manager all privileged EXEC command.


Stack Protocl Version
A switch with the same Cisco IOS software version as the stack master can 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. 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 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.

If the auto-upgrade feature is enabled on the new switch, the stack master automatically upgrades the new switch with the same software image running on a compatible stack member.

Connectivity to Stack Member
To debug a specific stack member, you can access it from the stack master by using the session stack-member-number privileged EXEC command. Only the show and debug commands are available in a CLI session to a specific stack member.
The switch stack is managed through a single IP address. The IP address is a system-level setting and is not specific to the stack master or to any other stack member. Stack members retain their IP addresses when you remove them from a switch stack (so, change the IP addresses of any switches that you remove from the switch stack to avoid IP conflict.)

Setting the Stack Port Speed to 10 Gbps
In a mixed stack of Catalyst 2960-X and 2960-S switches, you must set the stack port speed to 10 Gbps. This task is required in a mixed stack configuration and must be run on a Catalyst 2960-X switch in the switch stack before you add a 2960-S switch to the stack. Otherwise, the switches will not stack.