Administrator Guide

Stacking Prerequisites
Before you cable and configure a stack of the Aggregators, review the following prerequisites.
• All Aggregators in the stack must be powered up with the initial or startup configuration before you
attach the cables.
• All stacked Aggregators must run the same Dell Networking OS version. To check the version that a
switch is running, use the show version command. To download a Dell Networking OS version, go to
http://support.dell.com.
• Stacking is supported only with other Aggregators. A maximum of six Aggregators are supported in a
single stack.
• A maximum of four stack groups is supported on a stacked Aggregator.
• Interconnect the stack units by following the instructions in Cabling the Switch Stack.
• You cannot stack a Standalone IOA and a PMUX.
Master Selection Criteria
A Master is elected or re-elected based on the following considerations, in order:
1 The switch with the highest priority at boot time.
2 The switch with the highest MAC address at boot time.
3 A unit is selected as Standby by the administrator, and a fail over action is manually initiated or occurs
due to a Master unit failure.
No record of previous stack mastership is kept when a stack loses power. As it reboots, the election process
will once again determine the Master and Standby switches. As long as the priority has not changed on any
members, the stack will retain the same Master and Standby.
NOTE
: Each stack members’ role (including the Master and Standby) can be defined by the user at any
time by setting the priority.
If the entire stack is powered OFF and ON again, the unit that was the Master before the reboot will remain
the Master after the stack resumes operation. However, when a stack is powered on, all members are in sleep
mode for 5 seconds while waiting on the previous Master to join the stack. If the previous Master fails to join
within 5 seconds, the remaining members (including the Standby) elect a new Master.
Configuring Priority and stack-group
Perform the following steps to configure the priorities and stack-groups for each of the switches.
1 Set the priorities for the stack-unit.
CONFIGURATION mode
stack-unit unit-number priority 1-14
Dell(conf)# stack-unit 0 priority 12
Stacking 853