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 a several stack cables. Stackable switches logically become one switch. The major benefits of stacking have been enlisted below –
- Provides a single management interface for multiple units.
- Mitigates Spanning tree issues between switches.
- High performance and high bandwidth due to port bundling
- Uplink and downlink resiliency via Multichassis port bundling
- Power sharing across switch members.
- Improved backplane capacity
- Mitigation of single point of failure and faster convergence with removal of FHRP and STP protocols.
Diagram below is an example to show how stacking takes place with multiple switches –
Simple 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 stack. When a switch joins a switch stack it takes the next lowest switch stack 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 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
SW01#sh switch detail