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Catalyst 3850 Switch Hardware Installation Guide
OL-26779-02
Chapter 2 Switch Installation
Data Stack Cabling Configurations
Figure 2-5 and Figure 2-6 show data stacks of Catalyst 3850 switches with failover conditions. In
Figure 2-5, the StackWise cable is bad in link 2. Therefore, this stack provides only half bandwidth and
does not have redundant connections. In Figure 2-6, link 2 is bad. Therefore, this stack partitions into
two stacks, and the top and bottom switches become the active switch in the stack. If the bottom switch
is a member (not active or standby switch), it reloads.
Figure 2-5 Example of a Data Stack with a Failover Condition
Figure 2-6 Example of a Partitioned Data Stack with a Failover Condition
Power-On Sequence for Switch Data Stacks
Consider these guidelines before you power on the switches in a stack:
• The sequence in which the switches are first powered on might affect the switch that becomes the
active switch and the standby switch.
• There are two ways to elect an active switch:
–
If you want a particular switch to become the active switch, configure it with the highest
priority. Among switches with same priority, the switch with the lowest MAC address becomes
the active switch.
–
If you want a particular switch to become the active switch, power on that switch first. This
switch remains the active switch until a reelection is required. After 2 minutes, power on the
other switches in the stack. If you have no preference as to which switch becomes the active
switch, power on all the switches in the stack within 1 minute. These switches participate in the
active switch election. Switches powered on after 2 minutes do not participate in the election.
If changes are made to the stack without powering down the switches, the following results can occur:
• If two operating partial ring stacks are connected together using a stack cable, a stack merge can
take place. This situation reloads the whole stack (all switches in the stack).
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