Users Guide

240 Stacking
to the maximum distance supported by the transceiver on the stack links.
Note that PFC cannot be enabled on stacking ports — the system handles the
buffering and flow control automatically.
A single switch in the stack manages all the units in the stack (the stack
master), and the stack is managed by using a single IP address. The IP address
of the stack does not change, even if the stack master changes.
A stack is created by daisy-chaining stacking links on adjacent units. If
available, up to eight links per stack unit can be used for stacking (four in
each direction). A stack of units is manageable as a single entity when the
units are connected together. If a unit cannot detect a stacking partner on any
port enabled for stacking, the unit automatically operates as a standalone
unit. If a stacking partner is detected, the switch always operates in stacking
mode. One unit in the stack is designated as the stack master. The master
manages all the units in the stack. The stack master runs the user interface
and switch software, and propagates changes to the member units. To manage
a stack using the serial interface, the administrator must connect to the stack
master via the connect command or by physically connecting the cable to the
stack master.
A second switch is designated as the standby unit, which becomes the master
if the stack master is unavailable. The unit to be selected as the standby can
be manually configured, or the system can select the standby automatically.
When units are in a stack, the following activities occur:
• All units are checked for software version consistency.
• The switch Control Plane is active only on the master. The Control Plane
is a software layer that manages system and hardware configuration and
runs the network control protocols to set system configuration and state.
• The switch Data Plane is active on all units in the stack, including the
master. The Data Plane is the set of hardware components that forward
data packets without intervention from a control CPU.
• The running configuration is propagated to all units and the application
state is synchronized between the master and standby during normal
stacking operation. The startup configuration and backup configuration
on the stack members are not overwritten with the master switch
configuration.