Avaya 5000 Series Installation Manual page 29

Understanding stack types
This module describes the different stack types.
Due to stack parameters being associated with the base unit, the physical stack order depends
on the base unit position and whether the stack is configured cascade up (stack up) or cascade
down (stack down). This designation depends on the stack cabling arrangement.
The Unit Select switch is used to designate a switch in the stack as a base or non-base unit.
Sliding the switch to the right designates that switch as the base unit. Only one switch in a
stack may have the Unit Select switch in the base unit position. All other switches in the stack
must have the Unit Select switch in the left position which designates them as non-base units.
During the initial installation of the stack, the software automatically determines the physical
order of all units in the stack according to the position of the base unit within the stack.
Thereafter, the individual units maintain their original unit numbering, even if the position of
one or more units in the stack is changed.
For example, when the stack is initially powered, the base unit becomes unit 1 and the unit
that the base unit connects to (via the Cascade Down cable) becomes unit 2 (and the next unit
is unit 3 and so on), until the maximum stack configuration (up to 8 units for a 5500 Series
stack or a hybrid stack; up to 8 units for a pure 5600 Series stack) is reached. If the base unit is
changed to another unit in the stack, the new base unit keeps its original unit number in the
stack.
When a switch participates in a stack configuration, a stack MAC address is automatically
assigned during stack initialization. The stack MAC address is the base unit MAC address plus
1. If another unit in the stack is assigned as the base unit, the new stack MAC address is the
MAC address of the new base unit plus 1. The original stack IP address still applies to the new
base unit.
If an assigned base unit fails, the next unit in the stack order automatically becomes the new
temporary base unit. This change is indicated by the Base LED on the temporary base unit
LED display panel moving to a steady amber state.
This automatic failover is a temporary safeguard only. If the stack configuration loses power,
the temporary base unit will not power up as the base unit when power is restored. Also, if the
original unit rejoins the stack, it will not resume base unit status. For this reason, always assign
the temporary base unit as the base unit until the failed unit is repaired or replaced.
Important:
If the temporary base unit is not assigned as the new base unit, and the temporary base unit
fails, the next unit in the stack order becomes the temporary base unit. This process will
continue after successive failures until only two units are left in the stack.
Avaya Ethernet Routing Switch 5000 Series Installation
Placement options and cables
December 2010 29