OmniSwitch 6855 Series Stack Overview
Managing OmniSwitch 6855 Series Stacks
page 7-4
OmniSwitch 6855 Series Hardware Users Guide
September 2011
OmniSwitch 6855 Series Stack Overview
Users can configure OmniSwitch 6855-U24X switches into a single virtual chassis known as a
stack
. With
stacks, switching capacity can be easily expanded simply by adding additional switches to the stack. For
example, a user can start with a stack composed of two switches and add additional switches to that stack
as network demands increase over time.
Note.
Switches should be added one at a time in a stack.
Stacks also provide enhanced resiliency and redundancy features. If a switch in a stack goes down or is
taken offline, the other elements in the stack will continue to operate without disruption. In addition, when
a switch auto-synchronizes at boot-up, or if the user manually synchronize the switches (see
“Synchroniz-
ing Switches in a Stack” on page 7-37
for more information), operating software and configuration param-
eters are backed up on all switches in the stack. As a result, the original operating software and
configuration parameters can be easily recovered if corrupted or otherwise lost.
Note on Terminology.
In the user guides provided with your OmniSwitch 6855 Series switch, the terms
stack
and
virtual chassis
are interchangeable referring to OmniSwitch 6855 Series switches in a stacked
configuration. The terms
module
,
switch
,
slot
, and
element
are used to refer to individual switches within a
stacked configuration. The terms
Chassis Management Module (CMM)
and
management module
refer to
those switches operating in a stack either in the primary or secondary management roles. OmniSwitch
6855 Series switches operating in an idle role are essentially acting as network interface modules and
therefore may be referred to as
Network Interfaces (NIs)
.
Roles Within the Stack
In order to operate as a virtual chassis, switches within a stack are assigned specific roles. These roles
include primary and secondary management roles, idle status, and pass-through. For detailed descriptions
of each of these roles, including their practical functions within the virtual chassis, refer to the sections
below.
Primary and Secondary Management Modules
When OmniSwitches operate in a stack, one switch in the stack always assumes the
primary
management
role. This primary element is responsible for functions, such as software and configuration management,
web-based management (i.e., WebView), SNMP management, switch diagnostics, and software rollback.
One additional switch in the stack operates in a
secondary
management
role. This switch serves as a
backup, and is always ready to assume the primary management role in the stack if the switch with the
primary role fails or is taken offline for any reason.
Since the secondary module quickly and automatically assumes management responsibilities, switches
operating in idle mode elsewhere in the stack continue to pass traffic without disruption. This redundancy
provides effective safeguards for mission-critical network traffic and is one of the stack’s most important
failover features. Diagrams showing the management module failover sequence for stacks of three or more
switches and stacks of two switches are provided on pages
7-5
and
7-6
, respectively.
