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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 5 Managing Switch Stacks
Understanding Switch Stacks
4. The switch with the higher priority feature set and software image combination. These combinations
are listed from highest to lowest priority.
Note The noncryptographic images apply only to mixed stacks that include Catalyst 3750-E or 3750
switches running Cisco IOS Release 12.2(53)SE or earlier. Catalyst 3750-X switches and
Catalyst 3750-E or 3750 switches running later releases support only the cryprographic image.
–
IP services feature set and the cryptographic software image
–
IP services feature set and the noncryptographic software image
–
IP base feature set and the cryptographic software image
–
IP base feature set and the noncryptographic software image
Note In a switch stacks running the LAN base feature set, all switches in the stack must run the LAN
base feature set.
During the stack master switch election, differences in start-up times between the feature sets
determine the stack master. The switch with the shorter start-up time becomes the stack master.
For example, a switch running the IP services feature set has a higher priority than the switch
running the IP base feature set, but the switch running the IP base feature set becomes the stack
master because the other switch takes 10 seconds longer to start. To avoid this problem, upgrade the
switch running the IP base feature set to same feature set and software image as the other switch, or
manually start the master switch and wait at least 8 seconds before starting the new member switch
that running the IP base feature set.
5. The switch with the lowest MAC address.
A stack master retains its role unless one of these events occurs:
• The switch stack is reset.*
• The stack master is removed from the switch stack.
• The stack master is reset or powered off.
• The stack master fails.
• The switch stack membership is increased by adding powered-on standalone switches or switch
stacks.*
In the events marked by an asterisk (*), the current stack master might be re-elected based on the listed
factors.
When you power on or reset an entire switch stack, some stack members might not participate in the
stack master election. Stack members that are powered on within the same 20-second time frame
participate in the stack master election and have a chance to become the stack master. Stack members
that are powered on after the 20-second time frame do not participate in this initial election and become
stack members. All stack members participate in re-elections. For all powering considerations that affect
stack-master elections, see the “Switch Installation” chapter in the hardware installation guide.
The new stack master becomes available after a few seconds. In the meantime, the switch stack uses the
forwarding tables in memory to minimize network disruption. The physical interfaces on the other
available stack members are not affected during a new stack master election and reset.
After a new stack master is elected and the previous stack master becomes available, the previous stack
master does not resume its role as stack master.