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two. The Stack Link LED on the unit that is no longer receiving traffic from the next
unit up or down in the stack will begin flashing to indicate that the stack link is broken.
When the stack fails, a Master unit is selected from the two stack segments, either
the unit with the Master button depressed, or the unit with the lowest MAC address if
the Master button is not depressed on any unit. The stack reboots and resumes
operations. However, note that the IP address will be the same for any common
VLANs (with active port connections) that appear in both of the new stack segments.
To resolve the conflicting IP addresses, you should manually replace the failed link
or unit as soon as possible. If you are using a wrap-around stack topology, a single
point of failure in the stack will not cause the stack to fail. It would take two or more
points of failure to break the stack apart.
Note:
If a stack breaks apart, the IP address will be the same for any common VLANs
(with active port connections) that appear in both stack segments.
Resilient IP Interface for Management Access
The stack functions as one integral system for management and configuration
purposes. You can therefore manage the stack through any IP interface configured
on the stack. The Master unit does not even have to include an active port member
in the VLAN interface used for management access. However, if the unit to which
you normally connect for management access fails, and there are no active port
members on the other units within this VLAN interface, then this IP address will no
longer be available. To retain a constant IP address for management access across
fail over events, you should include port members on several units within the primary
VLAN used for stack management.
Resilient Configuration
If a unit in the stack fails, the unit numbers will not change. This means that when
you replace a unit in the stack, the original configuration for the failed unit will be
restored to the replacement unit. This applies to both the Master and Slave units.
Renumbering the Stack
The startup configuration file maps configuration settings to each switch in the stack
based on the unit identification number. If the units are no longer numbered
sequentially after several topology changes or failures, you can reset the unit
numbers using the “Renumbering” command in the web interface or CLI. Just
remember to save the new configuration settings to a startup configuration file prior
to powering off the stack Master.
Ensuring Consistent Code is Used Across the Stack
Consistent Runtime Code in Each Switch – The main board runtime firmware
version for each unit in the stack must be the same as the Master unit’s runtime
firmware. After Auto-ID assignment is completed, the Master unit checks the image
versions for consistency. If the firmware versions (i.e., runtime code) configured for
bootup on any slave units are not the same as those on the Master Unit, the stack
2-5
Stack Operations
2