Switch Stacking Basic Setup and Configuration Steps
Switch Stacking –
Switch stacking is a feature of certain Cisco access layer switches which allows for the creation
of a single logical device from many individual devices via a backside stack port connected by
several stack cables. Stackable switches logically to become one switch.
The major benefits of stacking have been enlisted below –
1. Provides a single management interface for multiple units.
2. Mitigates Spanning tree issues between switches.
3. High performance and high bandwidth due to port bundling
4. Uplink and downlink resiliency via Multichassis port bundling
5. Power-sharing across switch members.
6. Improved backplane capacity
7. Mitigation of single point of failure and faster convergence with the removal of FHRP and
STP protocols.
8.
The diagram below is an example to show how stacking takes place with multiple switches –
Steps to configure the switches in the stack:
Power up the switch which you want should be the master.
Attach the stacking cable to the rest of the members.
Power up the members one at a time and based on the order of your choice.
Example, if switch 2 is the 2nd switch, then power this switch after the master has been
powered up and stacking cable has been applied. This is followed by switch 3, switch 4,
etc.
Points to remember:
Ensure all switches are running the same IOS version, same Feature Set (example IP Base).
Once all switches are up, ensure you enable ―switch n priority XX―.
Priority value in the switch stack determines which switch will become the master. A higher
priority value for a stack member increases the probability of it being elected active switch and
retaining its stack member number. The priority value can be 1 to 15. The default priority value
is 1.
If priority value is a tie a switch with lower MAC address is elected as active after the current
active switch fails.
Another thing to note is the stack member number ‘n’ based on which the switches in the stack
get their port naming convention. The stack member number (1 to 9) identifies each member in
the switch stacking.
When a switch joins a switch stacking it takes the next lowest switch stacking member number.
Example Scenario –
Switch 1 is powered on to make it as active. Switch 1 takes the stack member number 1
and ports are numbered based on this stack member number.
Then Switch 2 is powered on and it takes the switch stack member number 2 and then
power on Switch 3 which will take switch stack member number 3.
You can check the switch stack member number using the command show switch.
Now from the active switch issue below command to assign priority values to the switches
in the stack:
switch stack-member-number priority new-priority-number
Example :
switch 1 priority 15
switch 2 priority 14
switch 3 priority 13
Example outputs:
SW01#sh switch
Switch/Stack Mac Address : 2c5a.0ff5.1000 – Local Mac Address
Mac persistency wait time: Indefinite
H/W Current
Switch# Role Mac Address Priority Version State
————————————————————————-
*1 Active f80b.cb4d.e000 15 V04 Ready
2 Standby 002c.c8fa.a580 14 V04 Ready
3 Member 2c5a.0ff5.1000 13 V04 Ready
SW01#sh switch detail
Switch/Stack Mac Address : 2c5a.0ff5.1000 – Local Mac Address
Mac persistency wait time: Indefinite
H/W Current
Switch# Role Mac Address Priority Version State
————————————————————————-
*1 Active f80b.cb4d.e000 15 V04 Ready
2 Standby 002c.c8fa.a580 14 V04 Ready
3 Member 2c5a.0ff5.1000 13 V04 Ready
