Switch Stacking Explained: Basis, Configuration & FAQs

What Is Switch Stacking?

Switch stacking is an important technology that connects multiple switches together. Those network switches can be connected through stack cables and operate as single logical unit, and more switch ports can be added, which can greatly increase the capacity of a network. Only stackable switches like FS S3900 and S3910 series gigabit switches support switch stacking.

Stacking switch together can improve network reliability and flexibility, increase bandwidth, and simplify networking. Stacking saves users out from managing multiple devices at the same time, especially in medium data centers or IT rooms. Users can add or remove switches in the stack unit as required without affecting the whole network performance. And if a link fails in the stack, other stacked switches will continue to work, which makes switch stacking a scalable and flexible solution for many network applications.

How Does Switch Stacking Work?

The switches in a stack are stacked together via DAC cables, optical transceivers or specialized stacking cables. In this switch stack, there are two main roles: stack master and stack slaves. Stack master is the core switch to manage other stack members and it stores the running configuration files for the whole switch stack. Generally, except for the stack master, the other switches in a stack are called stack slaves.

Users can log in to the stack system through the master switch, and perform unified configuration and management on all member switches of the stack system. If the master switch fails, the stack system will be switched for a period of time and a new master switch will be selected among the slave switches.

The number of switches in a stack varies from models to vendors. For example, FS S3900 series switches support up to six switches stacking together. However, no matter how many switches group into a stack, there is always a stack master that is assigned to control the operation of the switch stack. After stacking is enabled, users can manage and maintain the switch stack by performing in the master.

Typical Stack Topologies

There are two typical stack connection topologies, namely chain topology and ring topology. Both have their own advantages and disadvantages.

In a chain topology, the first and last stack members do not need to be physically connected, suitable for relatively long distance stacking. However, if a stack link fails, the stack splits.

In ring topology, when one of the stack links fails, the ring topology becomes chain topology, which does not affect the normal operation of the stack system. Therefore, ring topology offers higher reliability than chain topology.

However, the first and the last member switches in ring topology need to be physically connected. Therefore, ring topology is not suitable for long-distance transmission when stacking with DAC cables or other short-range stacking cables. The stacking of FS S3900 series switches mentioned above is a typical example using ring topology.

How to Configure Switch Stacking?

Generally, for switch stacking configuration, you should take the following steps:

1. Connect the switches physically using DAC/AOC or a combination of optical transceiver modules and fiber patch cables during a power failure. It should be noted that the number of stackable switches in a stack should not exceed the default number.

2. Turn on the power and configure the stack member ID, priority value, etc. on PC one by one until all the switches are configured.

3. After the stack is set up, observe indicators and save the configuration, then reboot all the switches in the stack. The role of each stack member will be allocated after the reboot.

4. After the reboot, the master switch will be the only switch with the privilege to run configuration. Check the interface information. The master switch will show all the interface.

Confusing Questions About Switch Stacking

Here are some frequently asked topics about switch stacking and other similar technologies, which will help you get a more comprehensive understanding of it.

1. Switch Stack vs Chassis

Both stacking switches and chassis provide benefits of multiple ethernet ports combined with the convenience of managing one device. However, each has its pros and cons that need to be noted.

A chassis switch is a network switch that contains a certain number of fixed slots, into which various line cards can be inserted. Different from a stack that is formed by several stackable switches connected through stacking cables, a chassis switch doesn't require switches to be connected because fixed modules are inside it. Compared with chassis switches, stackable switches require fewer upfront costs and better meet users’ needs for multiple scenarios, such as cross-area and long-distance transmission.

2. Switch Stacking vs MLAG

MLAG and stacking are often compared together because they are both scalable solutions that can provide link redundancy, reduce network complexity and improve network performance. However, there are also some differences between them.

MLAG refers to multi-chassis link aggregation group, tupically used in the data center access layer. The configuration and management of MLAG is more difficult than switch stacking, but the return on investment of MLAG is higher. While switch stacking is mostly seen in the enterprise access layer, performing better in its simple management and low operation and maintenance costs.

3. Switch Stacking vs Switch Cascading vs Clustering

Switch stacking, cascading and clustering have both similarities and differences in various aspects. The differences between them are listed below.

• Stacking and clustering are functions of network switches while cascading is a general way to connect switches.

• You can only take stackable switches of the same model from one vendor to stack them. But in terms of cascading, switches from different vendors can be cascaded, while a cluster must consist of switches from the same vendor.

• Stacking always has a limitation on the number of switches in a stack group. The exact quantities vary from series to vendors. There is no limitation on the number of switches that are cascaded together theoretically, but cascading too many switches may cause a broadcast storm, which will affect the entire network performance.

• The distance of the switches stacked together through physical stacking is limited by the length of the special stacking cable, but virtual switch stacking and switch cascading offer greater flexibility. Switch clustering can be either in the same location or at different layers.

• Management of the three switch connectivity technologies is different. Switch stacking is more easily managed because all the stackable switches in a group can be configured on the switch master, while cascaded switches are individually configured, with separate and individual configuration files for cluster members.

4. Switch Stacking vs Uplink vs Trunking

Uplink is a subject concept which means the uplink port of a switch is connected to another switch. Although it provides extremely limited bandwidth increase, switch uplinks support connecting switches from different product families or even different vendors, which provides great flexibility.

Trunking, on the other hand, is a connection between two layer 2 switches. It is a perfect fit for passing VLAN information between switches. Trunking is often used to form an inter-network including LANs, VLANs, and WANs, which enables packets encapsulated for multiple VLANs to cross exactly the same port as well as retaining the traffic separation among them.

Due to the similar function of stacking vs trunking vs uplink, there are confusing questions about them.

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