The switch with the highest priority value will be elected as the stack master. StackWise is a Cisco proprietary technology that is used to provide Layer 2 or Layer 3 connectivity between switches so that the stack of switches acts as a single device. When a StackWise configuration is used, the failure of a single switch will not result in an outage. Instead, the other switches in the stack will compensate for the failed switch. The switches are connected sequentially by stack cables: the first switch is connected to the second, the second switch is connected to the third, and so on until the last switch is connected to the first. If a stack cable is broken, the bandwidth of the stack will be reduced by 50 percent until the cable is fixed.

The stack master controls the operation of the stack. From the stack master, you can configure global features that apply to all switches in the stack as well as interface level features for individual stack members. The stack priority is a value from 1 through 15; by default, the priority value is set to 1. To change the stack priority, you should issue the switch stackid priority value command from global configuration mode. The following checklist is used to elect a stack master:
- The current stack master is elected as the stack master. Otherwise, the switch with the highest priority is elected stack master.
- If multiple switches have the same priority, the switch with a nondefault saved interface level configuration is elected stack master.
- If multiple switches have a nondefault saved interface level configuration, the switch with the highest feature set priority is elected stack master, based on the following hierarchy:
- IP services with cryptographic image
- IP services with noncryptographic image
- IP base with cryptographic image
- IP base with noncryptographic image
- If multiple switches have the same feature set, the switch with the shortest startup time is elected stack master.
- If multiple switches are still eligible, the stack member with the lowest Media Access Control (MAC)address is elected stack master.
The stack ID is not used to elect a stack master. Each stack member has a unique stack ID. By default, all switches use stack ID 1. However, if two switches attempt to take the same stack ID, the switch with the higher priority will retain the stack ID number and the other switch will automatically be assigned a new stack ID. Therefore, you need not make any configuration changes before adding a switch to a StackWise stack. However, you can manually configure a stack ID by issuing the switch current-stack-id renumber new-stack-id command from global configuration mode. The change will not take effect until the switch is reloaded.

IP addresses are not used to elect a stack master. In fact, a switch need not be configured with any IP addresses to become a stack member or stack master.