7.3.4 Role and selection of the master switch

A master switch is a switch that controls the entire stack and is elected according to three elements: the switch status, the master election preference, and the chassis MAC addressof the member switch.

This section describes the role of the master switch and the election of the master switch.

<Structure of this section>

(1) Master Switch Role

The master switch controls all member switches that make up the stack and their functions. All member switches in the stack operate according to the configuration of the master switch and control from the master switch.

The master switch is a representative of a member switch. When a user logs in to the stack from a remote operation terminal, the user must log in to the master switch.

The following operations can be performed on the logged-in master switch.

Editing the configuration
All member switch operations
Checking the operation messages and operation logs of all member switches

(2) Election of the master switch

The master switch is elected according to the following criteria:

(a) If you already have a master switch

Select an existing master switch as the master switch.

If a new member switch is connected to a stack that is already running on the stack port and started, the existing master switch remains in the master state. This allows you to add new member switches while preserving the stack's forwarding capabilities.

As an exception, if the master switch has a master election priority of 1 and there are other member switches with a master election priority of 2 or higher, a member switch with a master election priority of 2 or higher is selected as the master switch.

(b) With no one master switch

Select the backup switch as the master switch.

(c) When there is no master switch or one backup switch

Select the member switch with the highest master election priority as the master switch. If the master election priorities are the same, select the member switch with the lowest chassis MAC address as the master switch.

(d) When there are two master switches

(3) Example of Master Switch Election

The following shows an example of selecting a master switch.

(Example 1) Added a member switch to a single member switch stack.

When only one member switch in the stack is operating as a master switch, if another member switch is activated, the master state of the original master switch continues. Applicable to (a) of the selection criteria.

However, if the master election priority of the original master switch is 1 and the master election priority of the added member switch is 2 or higher, the added member switch is selected as the master switch. The original master switch reboots and becomes a member switch that is not the master switch in the stack.

(Example 2) Two member switches are activated simultaneously.

When two member switches connected to a stack port are activated simultaneously, the master switch is selected by comparing the master election priorities and the chassis MAC addresses. Applies to (c) of the selection criteria.

(Example 3) A master switch and a master switch are connected.

When two stacks constituting a stack are connected by a single member switch, they are compared in the order of master election priority and chassis MAC address. The master switch is selected. Applies to (d) of the selection criteria.

A member switch that was not selected as the master switch restarts and joins the stack of member switches that are selected as the master switch.

(4) How to fix the election of a master switch in a two-unit stack

There are two ways to make the selected member switch the master switch when starting all member switches in a two-member stack:

Set the master election priority to 2 or higher for the member switch that will be the master switch, and set the master election priority to 1 for the member switch that will not be the master switch.
Start the member switch that you plan to use as the master switch first. After starting up as a master switch, activate a member switch that is not intended to be a master switch.

(5) Master election priority

The master election priority is the priority for selecting the master switch from the member switches that make up the stack. You can use the configuration command switch priority to set the master election priority from 1 to 31.

A member switch with a higher master election priority is selected as the master switch in preference when all member switches in the stack are activated simultaneously. However, even if a member switch with a higher master election priority is added to the stack on which the master switch is already running, if the master election priority of the existing master switch is other than 1, the existing master switch continues the master state.

Master election priority 1 is a special priority. If two member switches are running and the master election priority of one member switch is 1 and the master election priority of the other member switch is 2 or more, the member switch with the master election priority of 2 or more is always selected as the master switch.

For example, if a member switch with a master election priority of 2 or higher is added to a stack consisting of a master switch with a master election priority of 1, the added member switch is selected as the master switch.

When the master switch is switched, communication stops temporarily because both the original master switch (master election priority 1) and the added member switch restart.

A member switch with the master election priority set to 1 is not elected as the master switch except in the following cases:

When there is only one member switch in the stack
When the master election priority of all member switches in the stack is 1

When adding a member switch to an existing stack, set the master election priority of the member switch to be added to 1. This is to prevent the added member switch from becoming the master switch when the existing master switch is restarted at the same time as the member switch is added, for example, due to a failure, and the configuration of the old member switch is replaced by the configuration of the added member switch. After the stack is built, the master election priority of the backup switch is changed to the master election priority set by the master switch.