Chapter 1
| Initial Switch Configuration
Stack Operations
– 70 –
Selecting the
Backup Unit
Once the Master unit finishes booting up, it continues to synchronize configuration
information to all of the Slave units in the stack. If the Master unit fails or is powered
off, a new master unit will be selected based on the election rules described in the
preceding section. The backup unit elected to serve as the new stack Master will
take control of the stack without any loss of configuration settings. To ensure a
logical fail over to the next unit down in the stack, place the Slave unit with the
lowest MAC address directly beneath the Master unit in the stack.
Recovering from
Stack Failure or
Topology Change
When a link or unit in the stack fails, a trap message is sent and a failure event is
logged. The stack will be rebooted after any system failure or topology change. It
takes two to three minutes to for the stack to reboot. If the Master unit fails, the
backup unit will take over operations as the new Master unit, reboot the stack, and
then select another backup unit after the stack finishes rebooting. Also note that
powering down a unit or inserting a new unit in the stack will cause the stack to
reboot. If a unit is removed from the stack (due to a power down or failure) or a new
unit added to the stack, the original unit IDs are not affected after rebooting, and a
new unit is assigned the lowest available unit ID.
Broken Link for Line and Wrap-around Topologies
All units in the stack must be connected via stacking cable. You can connect the
units in a simple cascade configuration from the top to the bottom unit. Using this
kind of line topology, if any link or unit in the stack fails, the stack will be broken in
two.
When the stack fails, a Master unit is selected from the two stack segments, either
the unit with the Master button enabled, or the unit with the lowest MAC address if
the Master button is not enabled 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
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