Users Guide

Stacking 233
stacking connections can be made between adjacent switch units to increase
the stacking bandwidth provided that all redundant stacking links have the
same port speed. It is strongly recommended that the stacking bandwidth be
kept equal across all stacking connections; that is, avoid mixing single and
double stacking connections within a stack. Up to eight redundant stacking
links operating at the same speed can be configured on a Dell EMC
Networking N4000 Series stack unit (four in each direction).
A stack of twelve Dell EMC Networking N4000 Series switches has an
aggregate front panel capacity of 5.760 terabits (not including the 40G ports).
Provisioning for 5% inter-stack capacity requires 280 gigabits of bandwidth
dedicated to stacking or all four 40G ports plus another twelve 10G ports.
Therefore, it is recommended that operators provision large stacking
topologies such that it is unlikely that a significant portion of the stack
capacity will transit stacking links. One technique for achieving this is to
distribute downlinks and transit links evenly across the stack vs. connecting
all downlinks/transit links to a single stack unit or to adjacent stacking units.
If Priority Flow Control (PFC) is enabled on any port in a Dell EMC
Networking N4000 Series stack, stacking is supported at distances up to 100
meters on the stacking ports. If PFC is not enabled, stacking is supported up
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.