Linksys SLM248G4S (G5) - Manual (Page 60)

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About Switch Stacking Appendx B
24/48-Port 10/100 + 4-Port Ggabt Reslent Clusterng Smart Swtch wth 2 Combo SFPs
If the incoming unit did not have an assigned Unit
ID (that is, it was in factory default mode), it will
be assigned the lowest available Unit ID by the
Master. It is strongly recommended that automatic
assigned unit ID mode be used since it provides
better resiliency to the stack.
If the incoming unit already has an assigned Unit
ID, and that Unit ID is unused in the current stack,
the incoming unit will keep its assigned Unit ID
and the Master will apply to it any configuration
relevant to that Unit ID.
If the incoming unit already has an assigned Unit
ID, and that Unit ID conflicts with a unit ID in the
current stack, the Master will reallocate a new
Unit ID to the incoming unit, giving it the lowest
available Unit ID (assuming, of course, that the
incoming unit does not have a manually assigned
Unit ID, which the Master cannot change).
If the incoming unit cannot be assigned an
available Unit ID for any reason (in the case of unit
replacement that can only happen if the incoming
unit has a manually assigned Unit ID), then it will
be effectively shut down—that is, it will not be
joined to the stack.
The stack Master will now carry out Unt and port
confguraton for the incoming unit.
Any configuration information the Master has
that is relevant to the number assigned to the
incoming unit will be applied. In particular, if the
incoming unit was assigned the same Unit ID of
the unit it replaces, then it will receive the same
configuration as the failed unit, to the extent
possible.
If the incoming unit is identical in makeup to the
replaced unit, the entire configuration of the replaced
unit will be applied to the incoming one and the stack
will go back to the state it was in before unit failure.
However, sometimes the incoming unit is not identical
to the unit that failed in these cases. The stack Master
will apply the configuration in the following manner:
If a 24-port unit replaces a failed 48-port unit,
then the ports of the incoming unit will be
configured according to the way the first 24
ports of the failed unit were configured.
(Note that the configuration of all 48 ports of the
failed unit is remembered, even though only the
first 24 are currently applied. If, in the future, a 48
port unit is inserted and assigned the same Unit
ID, it will be configured as the original failed 48-
port unit was configured).
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If a 48-port unit replaces a 24-port unit, then
the first 24 ports of the incoming unit will be
configured according to the way the ports of the
failed unit were configured, and the rest of the
ports of the incoming unit will be configured at
default settings.
If the units (the failed one and its replacement)
had/have uplink ports, then the first uplink of
the incoming unit will be configured as was the
first uplink of the failed unit, and so on.
Stack Master Failure and Replacement
In this example, the master unit fails in a running stack.
When notified of the failure, a system administrator
removes the failed unit and replaces it with another one.
When the unit fails, the stack Backup Master detects (via
the ongoing monitoring Master Discovery process) that
the master unit no longer responds and takes over as the
stack master. The backup master directs all other stack
members to route unit-to-unit traffic around the failed
unit using the ring topology of the stacking connections.
At the same time the stack Backup Master notifies the
system administrator (using SYSLOG messages and SNMP
traps) of the failure.
When the failed unit is disconnected from the stack, all
traffic will already be routed around it, and as long as all
other stacking connections are left intact, the stack should
continue to run.
When a new unit is inserted in the stack and powered up,
the following will happen:
The incoming unit will perform Master dscovery, and
perhaps participate in a Master Electon, as described
above.
If the incoming unit has a Unit ID of 1 or 2 (that
is, the unit is a master-enabled unit), then Master
Election will be initiated. However, since the
running stack Backup Master has a longer run
time, assuming that it has been running for more
then 10 minutes, it will remain elected as the stack
Master and the incoming unit will not become a
new stack Master. This may result in an incoming
unit using Unit ID=1, and serving as the stack
backup master, while the already running unit
with Unit ID=2 remains the active stack master.
The stack Master at this stage will carry out a Unt ID
allocaton and conflct resoluton process.
If the incoming unit did not have an assigned Unit
ID (that is, it was in factory default mode), it will
be assigned the lowest available Unit ID by the
Master. It is strongly recommended that automatic
assigned unit ID mode be used since it provides
better resiliency to the stack.
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