This tutorial explains the basic concepts of the Switch Stacking in detail. Learn what the Switch Stacking is and what benefits it provides in networking.
What is the Switch Stacking?
The Switch Stacking is a feature that allows us to configure multiple Cisco switches in a way that they appear as a single switch and act cooperatively. For example, if you have five individual Cisco switches, the Switch Stacking allows you to use all of them as a single large switch.
The following image shows an example of the Switch stacking.
Why was the Switch Stacking developed?
Traditionally, to add more ports to the current switch, we have two options. Either replace the existing switch with a new switch that has more ports or connects another switch to the existing switch using a cross-cable.
Let’s take a simple example.
A network is built by using a 100 ports' switch. All ports of this switch have been occupied. You are asked to add 5 more computers in this network. What will you do?
Will you buy a new 150 ports’ switch to replace the existing switch or will you buy a new 8 ports’ switch and connect it to the existing switch?
If you choose the first option: -
- You have to purchase a new switch of 150 ports.
- After this purchase, the current switch will be useless as it has only 100 ports and the network requires at least 105 ports.
If you select the second option: -
- You only need to purchase a new switch of 8 ports.
- After this purchase, the current switch will continue to work in the network.
Without any doubt, the first option is the easiest solution, but it not only cost a lot of money but also waste the existing device. Due to these reasons, administrators generally do not prefer this option.
Administrators usually prefer the second option as it not only reduces the cost but also utilizes the existing devices. But, the second option is not as easy as the first option.
When you connect two or more Cisco switches on the uplink ports through the Ethernet cables, the following will happen after the connection.
- Each switch will still work as an individual switch.
- Each switch will use its own MAC address table to make the frame forwarding decision.
- There will be no direct communication between switches.
- A lot of configuration and adjustment in settings will be required.
- Most uplink ports will be automatically blocked by the STP protocol.
To solve these issues, a new feature known as the Switch Stacking was developed by the Cisco.
Basic concepts of the Switch Stacking
A Cisco switch has its own IOS and works as a separate device. It uses the MAC address table to make the frame forwarding decision. Besides this, it supports and provides a lot of features and functions such as VLAN, VTP, STP, etc. For easier and remote management an IP address can also be assigned to it.
When we connect two or more Cisco switches on uplink ports, they do not lose their properties.
If we connect switches to expand the network, these features and functions are not only used to manage the network but also used to secure the network from unauthorized access.
If we connect switches to use them as a single large switch, these features and functions become the biggest obstacle.
Switch Stacking eliminates this obstacle in two steps. In the first step, it removes the ability to use these features and functions from all the participants. In the second step, it selects a master switch from all the participants and authorizes it to use these features and functions on behalf of all participants.
The technology used in the Switch Stacking is known as the Cisco StackWise technology.
Forming of the Switch Stacking
Only the switches which either have a stacking module or have a modular slot to install a stacking module can be used in the Switch Stacking. A stacking module has two ports. A special stacking cable is used to join all participants.
In stacking, all switches connect in a series making a ring. To complete the ring the last switch connects back to the first switch. The following image shows how switches connect with each other in the Switch Stacking.
All participant switches are kept in the same rack and room. Usually, they are placed on top of each other. The following image shows a stack of four switches.
Benefits of the Switch Stacking
The biggest benefit of the Switch Stacking is that it allows us to incrementally add more ports in the existing switch. By doing this, we can avoid the cost of upgrading to a bigger switch.
Other benefits of the Switch Stacking are the following.
- It reduces the management overhead.
- By reducing the required number of switches, it also reduces the cost of the network.
- It allows us to add or remove switches at any time without disrupting the running network or affecting its performance.
- Since all switches work as a single unit, STP does not block any port of the stack.
Key points
- You can add up to nine individual switches in a stack.
- Only the switch which has a special stacking module can join the stack.
- To connect stacking modules, a special stacking cable is used.
- All member switches of the stack select a master switch.
- The Master switch provides all switching related features and functions such as CDP, VTP, VLAN, STP, etc.
- Besides the master switch, no other switch is not authorized to run any switching related service.
- MAC address table is maintained only on the master switch and it references all ports on all physical switches.
- Each stack has only a single IP address and that is assigned to the master switch.
- Each stack has only one configuration file and it is managed on the master switch.
- When a new switch is added to the stack, the master switch automatically configures it.
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