Switch Stacking Explained with Benefits

Switch Stacking allows you to configure multiple Cisco switches so they appear as a single switch and act cooperatively. For example, if you have five individual Cisco switches, Switch Stacking lets you use them as a single large switch.

Traditionally, to add more ports to the current switch, you have two options. Either replace the existing switch with one with more ports, or connect another switch to it using a cross-cable. Let’s take an example.

A network is built by using a 100-port switch. All ports on this switch are occupied. You are asked to add 5 more computers to this network. What will you do?

Will you buy a new 150-port switch to replace the existing one, or a new 8-port switch and connect it to the existing one?

If you choose the first option: -

• You have to purchase a new switch with 150 ports.
• After this purchase, the current switch will be useless, as it has only 100 ports, while the network requires at least 105.

If you select the second option: -

• You only need to purchase a new 8-port switch.
• 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 costs a lot of money but also wastes 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 costs but also uses 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 using Ethernet cables, the following things happen after the connection.

• Each switch will still work as an individual switch.
• Each switch will use its own MAC address table to make frame-forwarding decisions.
• 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 address these issues, Cisco developed a new feature called Switch Stacking.

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 forwarding decisions. Besides this, it supports many features and functions, such as VLAN, VTP, and STP. For easier remote management, an IP address can also be assigned to it. When you connect two or more Cisco switches on uplink ports, they retain their properties.

If you connect switches to expand the network, these features and functions are used not only to manage the network but also to secure it from unauthorized access. If you 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 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 Switch Stacking is called Cisco StackWise.

Forming of the Switch Stacking

Only switches that have a stacking module or a modular slot for a stacking module can be used in Switch Stacking. A stacking module has two ports. A special stacking cable is used to join all participants.

In stacking, all switches are connected in series to form a ring. To complete the ring, the last switch connects back to the first switch. The following image shows how switches connect in 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 you to incrementally add more ports to the existing switch. By doing this, you can avoid the cost of upgrading to a bigger switch. Other benefits of the Switch Stacking are the following.

• It reduces the management overhead.
• Reducing the required number of switches also lowers the network's cost.
• It allows you 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 that 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, and STP.
• Besides the master switch, no other switch is authorized to run any switching-related service.
• The 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.

Conclusion

Switch stacking is an effective solution for expanding network capacity, simplifying management, and reducing costs. By allowing multiple switches to operate as a single unified device, stacking streamlines network configuration, maintenance, and scalability. For organizations seeking flexibility, reliability, and efficiency in their network infrastructure, switch stacking offers clear advantages over traditional methods.