Alcatel OS6850-P48 User Guide - Page 167

Managing OmniSwitch 6850/6850E Series Stacks OmniSwitch 6850/6850E Series Stack Overview OmniSwitch 6850/6850E Series Stack Overview Users can configure up to eight switches, in any combination of chassis types, 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 up to six 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 "Synchronizing Switches in a Stack" on page 6-39 for more information), operating software and configuration parameters 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. The terms stack and virtual chassis are interchangeable referring to 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. 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 switches 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, webbased 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 6-6 and 6-7, respectively. OmniSwitch 6850/6850E Series Hardware Users Guide June 2011 page 6-5