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Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter5 Managing Switch Stacks
Understanding Stacks
3. The switch that is not using the default interface-level configuration.
4. The switch with the higher priority switch software version. These switch software versions are
listed from highest to lowest priority:
Cryptographic IP services image software
Noncryptographic IP services image software
Cryptographic IP base image software
Noncryptographic IP base image software
If two or more switches in the stack use different software images, a switch running the
noncryptographic IP base image might be selected as the master. A switch running the cryptographic
IP services image takes 10 seconds longer to start than does the switch running the noncryptographic
image. The switch running the cryptographic image is excluded from the master election process
that lasts 10 seconds. To avoid this problem, upgrade the switch running the IP base image to a
software release later than Cisco IOS Release 12.1(11)AX, or manually start the master and wait at
least 8 seconds before starting the new member.
5. The switch with the lowest MAC address.
A stack master keeps its role unless one of these events occurs:
The stack is reset.*
The master is removed from the stack.
The master is reset or powered off.
The master fails.
The 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 stack, some stack members might not participate in the master
election.
All members participate in re-elections.
Members that are powered on within the same 20-second time frame participate in the master
election and have a chance to become the master.
Members that are powered on after the 20-second time frame do not participate in this initial election
and only become members.
Note Stack master elections occur over a 10-second time frame on switches running releases earlier than Cisco
IOS Release 12.2(20)SE3.
The new master is 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 while a new stack master is elected and is resetting.
When a new master is elected and the previous stack master becomes available, the previous master does
not resume its role as stack master.
For all powering considerations that affect stack-master elections, see the “Switch Installation” chapter
in the hardware installation guide.