White Paper

Making a Specific Switch the Stack Master and Master Election Rules

Stack Election Rules

When multiple physical members are present in the stack, one of the members will be elected as the stack master.

There can only be one master and up to three backups 1:3.

The election rules used by FlexStack in choosing a master are applied in this order:

1. Switch that is the current master

2. Switch with higher priority

3. Switch that has configuration file

4. Switch with longest uptime

5. Switch with lowest MAC address block

When new switches join an existing stack, then rules 1 and 2 will be applied.

When two standalone switches are joined together, having no switch priority configured, and both having existing

configuration files, then the switch with the longest uptime will be chosen.

To have a specific member elected as master, two methods can be used.

1. Set the priority of the desired member to be higher than all other members. This is rule 2.

a. Example of configuring member 1 to have priority 14:

C2960-48(config)#switch 1 priority 14

b. A reboot of the current master will be required after this to change the active master. Just configuring the

priority will not by itself change the active master. Save the configuration before rebooting.

2. When the switches boot, and after they have completed power-on self-test (POST), there is a delay of

approximately 2 minutes while the switches wait for all switches that could be in the stack to boot. This 2-

minute delay is called the election window. Network administrators can take advantage of this window by first

powering up only the desired master switch. Once the election window closes, this switch will become the

master of a stack of one. Any subsequent switches that boot after the first switch will become members of the

existing stack.

The switch with the lowest MAC address is used to break the tie in those scenarios in which the other rules cannot

be applied.

It is desirable for network administrators to make a specific switch in the stack the master. This could be the

topmost switch or the bottommost switch in the stack. For switch identification purposes, knowing how the

members are connected is an advantage. If a switch needs to be replaced, then it is very convenient to know

where that switch is located in relation to the other stack members.

Note: All Cisco Catalyst 2960-S, 2960-X, and 2960-XR LAN Base switches are equally capable of becoming the

stack master. Physical place in the stack does not affect switch behavior.