Switch stacking is an important function of network switches. Those switches can be connected together and operate as one logical unit, then all switch ports can be added to which can increase the capacity of a network greatly. And only stackable switches like FS S3900 series gigabit switches support the switch stacking.
Stacking switch together can optimize network performance. And it 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 switches will continue to work, which makes switch stacking a scalable and flexible solution for many network applications.
The switches in a stack are stacked together via DAC cables, optical transceivers or a specialized stack cables. In this switch stack, there are two main roles: stack master and stack slaves. Generally, except for the stack master, the other switches in one stack are called 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. Users can log in to the stack system through the master member 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 is 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.
There are two typical stack connection topologies, namely chain topology and ring topology. They both have pros and cons.
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 a ring topology, when one of the stack links fails, the ring topology becomes a chain topology, which does not affect the normal operation of the stack system. Thus, it has higher reliability than a chain topology. However, the first and the last member switches in a ring topology need to be physically connected. Therefore, it is not suitable for long distance transmission when stacking with DAC cables or other short-range stacking cables. FS S3900 series switches stacking mentioned above is a typical example using a ring topology.
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 when power is off. It should be noted that the number of the switches in a stack are not supposed to be more than the defaulted number.
2. Switch 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 rebooting.
4. After rebooting, the master switch will be the only one switch with the privilege to run configuration. Check the interface information. The master switch will show all the interface.
For more details, see the following support article: Stack Configuration on FS S3900 Series Switches.
Here are some frequently asked topics about switch stacking which will help to get a more comprehensive understanding of it.
Physical stack is a technology that switches are stacked via special stacking interfaces and stacking cables while virtual stack is realized via general interfaces of the switches. Their advantages and disadvantages are shown in the table below.
More choice for stacking cables;
Distance is not limited
|Relatively poorer coupling and stability|
|Physical Stack||Better coupling and stronger stability||
Stacking cables provided by vendors are expensive;
Stacking cables are limited in distance
Actually physical stacking is only adopted in a few vendors' stackable switches because there remains a technical barrier. In the network switch market, stackable switches mainly use virtual stacking, such as FS S3900 stackable switches.
Both stacking switches and chassis provide benefits of multiple ports combined with the convenience of managing one device. However, each has its pros and cons you need to consider.
A chassis switch is a network switch that contains a certain number of fixed slots, into which various types of line cards can be inserted. Different from a stack that is formed by several stackable switches that are connected through fiber cables, a chassis switch doesn't need to connect switches 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.
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, which refers to multi-device link aggregation group, is commonly used in the data center access layer. The configuration for MLAG is less than switch stacking and the return on investment of MLAG is higher. While switch stacking is mostly seen in the enterprise access layer, better in its simple management and low operation and maintenance costs.
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 and stack them, but in terms of cascading, switches from different vendors can be cascaded, while a cluster must be the 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 note that cascading too many switches may cause a broadcast storm, which will affect the whole network performance.
The distance of the switches that are stacked together via the use of physical stacking is limited by the length of the special stacking cable, but virtual switch stacking and switch cascading offer more flexibility. Switch clustering can be either in the same location or at different layers.
Management of the three switch-connecting technologies is different. Stacking switches are more easily managed because all the stackable switches in a group can be configured on the switch master, while cascaded switches are individually configured and cluster members have separate and individual configurations files.
Uplink is a subject concept which means so-called uplink port of a switch is connected to another switch. Despite it provides extremely limited bandwidth increase, switch uplink supports connecting switches from different product families or even different vendors, which provides great flexibility.
While trunking refers to 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 retain the traffic separation among them.
Due to the similar function of stacking vs trunking vs uplink, there are confusing questions about them. You can find more details about the contrast among these three connecting methods from Switch Stacking vs Trunking vs Uplink: Which Is Best to Connect Switches?