Administrator Guide

Stack Management Roles
The stack elects the management units for the stack management.
• Stack master — primary management unit, also called the master unit.
• Standby — secondary management unit.
The master holds the control plane and the other units maintain a local copy of the forwarding databases. From the stack master you
can congure:
• System-level features that apply to all stack members.
• Interface-level features for each stack member.
The master synchronizes the following information with the standby unit:
• Stack unit topology
• Stack running conguration (which includes ACL, LACP, STP, SPAN, and so on.)
• Logs
The master switch maintains stack operation with minimal impact in the event of:
• Switch failure
• Inter-switch stacking link failure
• Switch insertion
• Switch removal
If the master switch goes o line, the standby replaces it as the new master and the switch with the next highest priority or MAC
address becomes standby.
NOTE: For the MXL switch, the entire stack has only one management IP address.
Stack Master Election
The stack elects a master and standby unit at bootup time based on two criteria.
• Unit priority — User-congurable. The range is from 1 to 14. A higher value (14) means a higher priority. The default is 0. To
remove the stack-unit priority and set the priority back to the default value of zero, use the no stack-unit priority
command.
• MAC address (in case of priority tie) — The unit with the higher MAC value becomes the master unit.
To view which switch is the stack master, enter the show system command. The following example shows sample output from an
established stack.
A change in the stack master occurs when:
• You power down the stack master or bring the master switch oine.
• A failover of the master switch occurs.
• You disconnect the master switch from the stack.
When a stack reloads and all the units come up at the same time; for example, when all units boot up from ash, all units participate
in the election and the master and standby are chosen based on the priority or MAC address.
When the units do not boot up at the same time, such as when some units are powered down just after reloading and powered up
later to join the stack, they do not participate in the election process even though the units that boot up late may have a higher
priority congured. This happens because the master and standby have already been elected, hence the unit that boots up late joins
only as a member.
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Stacking