two. The Stack Link LED on the unit that is no longer re ceiving traffic f rom th e ne xt
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 segmen ts, eit her
the unit with the Master button depressed, or the unit with the lowest MAC add ress if
the Master button is not depressed on any unit. The stack reboo ts and resume s
operations. However, note that the IP address will be the same for any common
VLANs (with active port connections) that appear in both of th e ne w stac k se gme nts.
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 m ore
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 conf iguration
purposes. You can therefore manage the stack through any IP int erface config ured
on the stack. The Master unit does not even hav e to include an activ e port membe r
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 with in the prim ary
VLAN used for stack management.

Resilient Configuration

If a unit in the stack fails, the unit numbers will n ot change. T his mean s that whe n
you replace a unit in the stack, the original configu ration fo r the fai led unit will be
restored to the replacement unit. This applies to both the Maste r and Slave un its.
Renumbering the Stack
The startup configuration file maps configuration settings to eac h switch in th e stack
based on the unit identification number. If the units are no longer numbe red
sequentially after several topology changes or failures, you can reset the un it
numbers using the “Renumbering” command in the web interface or CLI. Ju st
remember to save the new configuration settings to a startup co nfiguration 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 run time firm ware
version for each unit in the stack must be the sa me as the Master unit ’s runtim e
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 M aster Un it, the stack

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Stack Operations

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