Switch: StackWise introduction

Understanding Stackwise technology

1.       For access Layer 3 switch only Catalyst 3750 has the ability to stack.

2.       Mixed stacking is possible between two different models, such as 3750-X and 3750-E can stack with each other.

3.       Homogenous stack is possible between two same models, such as 3750-X and 3750-X can stack with each other.

4.       One stack unit has a single IP address for managing the stack unit.

5.       A switch stack has up to 9 stack members connected through stack-wise plus ports.

6.       A switch stack always has one stack master.

Stack Master and stack member relationship

7.       A stack unit has one Stack Master and several Stack members.

8.       The Stack master is a single point of Stack-wide management that is the configuration of a stack unit should be done from the Stack Master switch.

9.       A stack unit is identified by the network by its bridge ID, and if Layer 3 switch by its router’s mac address. The bridge ID and the router’s mac address are determined by the Stack master.

10.   Every Stack member is identified by their own stack member number.

11.   Every stack member is eligible to become a stack master. Once the stack master is unavailable, stack master election will start among the stack members. Stack members with the highest stack member priority value wins the stack master election.

12.   The stack master contains the saved and running configuration of the switch stack. Stack members also keep copies of the identical configuration for backup purposes.

13.   The single IP address is to manage the switch stack, the same IP address can still manage the stack even the Stack master or stack member is removed from the stack.

Stack member priority values

14.   The priority value can be between 1 and 15.

15.   The default priority is 1.

16.   Stack member priority value can be displayed by using show switch command.

17.   Stack member priority value can be modified by switch stack-member-number priority new-priority value command in global configuration mode.

Stack master election

18.   Stack master is elected with the highest priority value.

19.   Cisco recommends the intended Stack master to have the highest priority value so that the switch can still maintain Stack master role even after re-election.

20.   The switch with the higher priority feature set and image combination will become the stack master, the below feature set and image combinations are arranged from highest to lowest priority:

a.       IP services feature set and cryptographic image

b.      IP services feature set and non-cryptographic image

c.       IP base feature set and cryptographic image

d.      IP base feature set and non-cryptographic image

21.   The switch with the shortest start up time becomes the stack master. This will supercede the switch’s priority value for example a switch with the highest priority value will not be a stack master if it boots up 10s later than the other switch, the switch that’s boot up the earliest will become the stack master despite its lower priority value.

22.   The switch with the lowest MAC address becomes the stack master.

Stack master re-election events

1.       Stack master fails.

2.       Stack master was removed.

3.       Switch stack was reset.

4.       Switch stack was reset or powered off.

5.       New switch was introduced into the switch stack.


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