White Paper

For brand-new switches, with no configuration, all powered at the same time, the switch with the lowest MAC

address will be the master. It is not practical to orient and deploy switches in a stack based on MAC address.

To create a new stack with the correct physical member as the master, the network administrator must use the

“uptime” rule. To reliably make any new switch the master, it must be powered up first. Subsequent switches

should not be powered up until the election window is complete and the first switch has become the master. This is

about 2 minutes, or when the system LED and the MSTR LED turn solid green.

To change the master after the stack of Cisco Catalyst 2960 switches has been created and set up, use the global

configuration command “switch X priority Y,” where X is the member number that is desired to be the master, and

Y is the priority value to use. To make member X the master, you must assign it a priority value higher than that of

the current master.

By default, all switches have priority 1. To view switch priority, use the “show switch” command:

C2960-48#show switch

Switch/Stack Mac Address : 0022.bdc4.1d80

H/W Current

Switch# Role Mac Address Priority Version State

----------------------------------------------------------

*1 Master 0022.bdc4.1d80 1 1 Ready

2 Member 0022.bdc4.2300 1 1 Ready

3 Member ec30.912e.2380 1 1 Ready

4 Member 0026.0ac1.3e00 1 1 Ready

To make sure that member 1 will become the master, the priority should be changed to any value greater than 1.

Here is an example showing member 1 assigned priority 14:

C2960-48#config term

Enter configuration commands, one per line. End with CNTL/Z.

C2960-48(config)#switch 1 priority 14

If a switch other than the master is given higher priority, as shown in the preceding command, there will not be an

immediate switchover of the master. The master will not change until the current master is rebooted, forcing a

stack master election of remaining members.

Setting the priority is important when merging two stacks. Existing stacks are merged when the FlexStack cable

from one stack is connected to another stack. It only takes one cable to merge two stacks. When two existing

stacks are merged, a master election takes place. When two stacks merge, both stacks already have a stack

master, so the first rule is not applied. The best way to determine which stack master will continue to be master of

the new combined stack is with the priority value.

Note: A standalone switch is still a stack of one member. Adding a standalone switch that has been powered up

to an existing stack is a still a stack merge. If the standalone switch has a higher priority than the master of the

other stack, then the standalone switch will become the master of the combined stack. During a stack merge the

new master is chosen during the election process. The election process is used during a stack merge and at stack

power-on time.

As always during a stack merge, new members are rebooted after the election process has completed. Existing

members are not booted.