Switch Stacking Explained: Basis, Configuration & FAQs
What is Switch Stacking?
Switch stacking is an important technology that connects multiple switches together. Stackable switches can improve network scalability, reliability and flexibility, increase bandwidth, and simplify networking. Stacking saves users from managing multiple devices simultaneously, 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 stackable switches will continue to work, which makes switch stacking a scalable and flexible solution for many network applications.
How Does Switch Stacking Work?
Stackable switches are connected via DAC cables, optical transceivers or specialized stack cables. 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 stacking. 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 switch stacking system. If the stack master 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 model to vendor. For example, FS S3900 series switches support up to six switches stacking together. However, no matter how many switches are grouped into a stack, there is always a stack master that is assigned to control the operation of the switch stacking.
Typical Switch Stacking Topologies
There are two typical switch stacking topologies, namely chain topology and ring topology. Both have their own advantages and disadvantages.
Chain topology: The first and last stack switches do not need to be physically connected, which is suitable for relatively long-distance stacking. However, if a stack link fails, the whole stack will split.
Ring topology: The first and the last stack 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 stack cables. When one of the stack links fails, the ring topology becomes chain topology, which does not affect the normal operation of the switch stacking system. Therefore, ring topology offers higher reliability than chain topology. The stacking of FS S3900 series switches mentioned above is a typical example of 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 optic cables during a power failure. It should be noted that the number of stackable switches should not exceed the default number.
2. Turn on the power and configure the stack member ID, priority value, etc. on the PC one by one until all the stackable switches are configured.
3. After the switch stacking 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 stack master will be the only switch with the privilege to run configuration. Check the interface information. The master switch will show all the interfaces.
If you want to learn more about detailed stacking configuration operations, you can refer to the S3900 Series Switches Configuration Guide.
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. Stackable Switch vs Chassis Switch
Both stacking switches and chassis provide the benefits of multiple ethernet ports combined with the convenience of managing one device.
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 stackable switch, a chassis switch doesn't require switches to be connected because there are fixed modules 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 refers to a multi-chassis link aggregation group, typically used in the data center access layer. The configuration and management of MLAG is more difficult than switch stacking, but its return on investment is higher. Switch stacking is mostly seen in the enterprise access layer, simplifying management and reducing 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.
Switch stacking always has a limitation on the number of switches in a stack group. There is no limitation on the number of switches that are cascaded together theoretically, but cascading too many switches may impact network performance.
The distance of stackable switches 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.
Switch stacking is more easily managed, while cascaded switches are individually configured, with separate and individual configuration files for cluster members.
4. Switch Stacking vs Uplink vs Trunking
Uplink means the uplink port of a switch is connected to another switch. Switch uplinks support connecting switches from different series and vendors, which provides great flexibility. Trunking is a connection between two layer 2 switches. It is commonly used to build interconnected networks, including LANs, VLANs, and WANs, suitable for transmitting VLAN information between switches. You can read the article Switch Stacking vs Trunking vs Uplink: Which to Choose for Connecting Switches? to learn more.