Administrator Guide

Failover Roles
If the stack master fails (for example, is powered off), it is removed from the stack topology.
The standby unit detects the loss of peering communication and takes ownership of the stack management, switching from the standby
role to the master role. The distributed forwarding tables are retained during the failover, as is the stack MAC address. The lack of a
standby unit triggers an election within the remaining units for a standby role.
After the former master switch recovers, despite having a higher priority or MAC address, it does not recover its master role but instead
takes the next available role.
To view failover details, use the show redundancy command.
MAC Addressing on Stacks
The stack has three MAC addresses: the chassis MAC, interface MAC, and null interface MAC.
All interfaces in the stack use the interface MAC address of the management unit, and the chassis MAC for the stack is the master’s
chassis MAC. The stack continues to use the master’s chassis MAC address even after a failover. The MAC address is not refreshed until
the stack is reloaded and a different unit becomes the stack master.
NOTE: If the removed management unit is brought up as a standalone unit or as part of a different stack, there is a
possibility of MAC address collisions.
A standalone is added to a stack. The standalone and the master unit have the same priority, but the standalone has a lower MAC address,
so the standalone reboots. In the second example, a standalone is added to a stack. The standalone has a higher priority than the stack, so
the stack (excluding the new unit) reloads.
Example of Adding a Standalone with a Lower MAC Address to a Stack
----------STANDALONE BEFORE CONNECTION---------------
Standalone#show system brief
Stack MAC : f8:b1:56:29:fc:21
Reload-Type : normal-reload [Next boot : normal-reload]
-- Stack Info --
Unit UnitType Status ReqTyp CurTyp Version Ports
----------------------------------------------------------------------------------
1 Member not present
2 Member not present
3 Member not present
4 Management online S3148P S3148P 1-0(0-4679) 54
5 Member not present
6 Member not present
7 Member not present
8 Member not present
9 Member not present
10 Member not present
11 Member not present
12 Member not present
-- Module Info --
Unit Module No Status Module Type Ports
---------------------------------------------------------------------------
4 1 not present No Module 0
-- Power Supplies --
Unit Bay Status Type FanStatus FanSpeed(rpm)
---------------------------------------------------------------------------
4 1 up AC up 7824
4 2 absent absent 0
-- Fan Status --
Unit Bay TrayStatus Fan0 Speed Fan1 Speed
------------------------------------------------------------------------------------
4 1 up up 7058 up 6956
Speed in RPM
Standalone#show system | grep priority
798
Stacking