Reference Guide

Stacking | 853
• Interface-level features for each stack member
The master synchronizes the following information with the standby unit:
• Stack unit topology
• Stack running Configuration (which includes ACL, LACP, STP, SPAN, etc.)
• 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 off line, the standby replaces it as the new master and the switch with the next
highest priority or MAC address becomes standby.
Stack Master Election
By default, the stack determines a master and standby unit at bootup time by electing the units with the
highest MAC addresses.
You can pre-configure the units which will be elected master and standby by assigning higher priorities to
these units. (By default, all stack units have priority 0. Valid priority values are from 0 to 14. A higher
value means a higher priority. To remove the stack-unit priority and set the priority back to the default
value of zero, use the
no stack-unit priority command.)
If you add a standalone unit, which has the same priority as the master stack unit, the standalone unit joins
the stack as a member unit.
To view which switch is the stack master, use the
show system command. Figure 48-2 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 offline.
• A failover of the master switch occurs.
• You disconnect the master switch from the stack.
When a stack reloads, the stack master is determined as follows:
Note: An S5000 switch stack has only one management IP address.
Note: The units with the highest MAC addresses become master and standby only if no priorities are
configured. The MAC address of the master unit is refreshed only when the stack is reloaded and a
different unit becomes the stack manager.