Specifications

244 Implementing IBM System Networking 10Gb Ethernet Switches
򐂰 The active Master is rebooted with the boot configuration set to factory defaults (clearing
the Backup setting).
Master failover
When the Master switch is present, it controls the operation of the stack and pushes
configuration information to the other switches in the stack. If the active Master fails, then the
designated Backup (if one is defined in the Master’s configuration) becomes the new acting
Master and the stack continues to operate normally.
Secondary backup
When a Backup takes over stack control operations, if any other configured Masters (acting
as Member switches) are available within the stack, the Backup selects one as a secondary
Backup. The primary Backup automatically reconfigures the secondary Backup and specifies
itself (the primary Backup) as the new Backup in case the secondary fails. This action
prevents the chain of stack control from moving too far from the original Master and Backup
configuration intended by the administrator.
Master recovery
If the prior Master recovers in a functioning stack where the Backup assumed stack control,
the prior Master does not reassert itself as the stack Master. Instead, the prior Master
assumes a role as a secondary Backup to avoid further stack disruption.
Upon stack reboot, the Master and Backup resume their regular roles.
No backup
If a Backup is not configured on the active Master, or the specified Backup is not operating,
then if the active Master fails, the stack reboots without an active Master.
When a group of stacked switches are rebooted without an active Master present, the
switches are considered to be isolated. All isolated switches in the stack are placed in a
WAITING state until a Master appears. During this WAITING period, all the external ports and
internal server ports of these Member switches are placed into operator-disabled state.
Without the Master, a stack cannot respond correctly to networking events.
Stack Member identification
Each switch in the stack has two numeric identifiers, as follows:
򐂰 Attached Switch Number (asnum): An asnum is automatically assigned by the Master
switch, based on each Member switch’s physical connection in relation to the Master. The
asnum is used as an internal ID by the Master switch and is not user-configurable.
򐂰 Configured Switch Number (csnum): The csnum is the logical switch ID assigned by the
stack administrator. The csnum is used in most stacking-related configuration commands
and switch information output. It is also used as a port prefix to distinguish the relationship
between the ports on different switches in the stack.
You should use asnum 1 and csnum 1 to identify the Master switch. By default, csnum 1 is
assigned to the Master. If csnum 1 is not available, the lowest available csnum is assigned to
the Master.
Configuring a stack
This section provides procedures for creating a stack of switches. The high-level procedure is
as follows:
1. Choose one Master switch for the entire stack.
2. Set all stack switches to stacking mode.