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How to Connect Multiple Switches together

With the development of Ethernet, the monitoring and management of Ethernet is becoming more and more complicated. Only one switch can’t users’ demand at some points. Then people will connect multiple switches together. The below content will show you three methods.

Method 1: Cascade

Cascading means that two or more switches are connected to each other in a certain way. Multiple switches can be cascaded in various ways as needed. In a larger local area network such as a campus network (campus network), a plurality of switches generally form a cascaded structure of a bus topology, a tree topology or a star topology according to their performance and usage.

The metropolitan area network(MAN) is generally divided into three levels from top to bottom: core layer, convergence layer, and access layer. The core layer generally adopts Gigabit Ethernet technology, the aggregation layer uses  1000M/100M Ethernet technology, and the access layer employs  100M/10M Ethernet technology.

The broadband metropolitan area network of this structure is actually formed by the cascade connection of many switches at various levels. Several aggregation switches are connected to the core switch. Then the aggregation switches are connected to several cell center switches. The cell center switches are connected to several building switches, and the building switches are connected to several floor (or unit) switches (or hub).

The switches are generally cascaded through common user ports while some switches provide special cascade ports (Uplink Port). The difference between these two ports is only that the common port conforms to the MDIX standard, while the cascade port (or upstream port) conforms to the MDI standard. As a result, the wiring methods in the two modes are different: when two switches are cascaded through common ports, the cables between ports are crossover cables; Cable (Straight Through Cable).

In order to facilitate cascading, some switches provide a dual-purpose port, which can be set to  MDI or  MDIX through switches or management software. Further, all or some ports on some switches have MDI/MDIX self-calibration functions, which can automatically distinguish the type of network cable, which is more convenient for cascading.

When cascading with switches, pay attention to the following issues. In principle, Ethernet switches of any manufacturer and any type can be cascaded with each other.  But in some special cases, two switches cannot be cascaded. The number of cascaded layers between switches is limited. The most fundamental principle for successful cascading is that the distance between any two nodes cannot exceed the maximum span of the media segment. When multiple switches are cascaded, it should be ensured that they all support the  Spanning-Tree protocol to prevent loops in the network and allow the existence of redundant links.

When cascading, you should try your best to ensure that the trunk links between switches have sufficient bandwidth, which can be achieved through full-duplex technology and link aggregation technology. When the switch port adopts the full-duplex technology, not only the throughput of the corresponding port is doubled, but also the relay distance between switches is greatly increased, making it possible to cascade multiple switches distributed in different places and within a long distance. Link aggregation is also called port aggregation, port bundling, and link expansion combination, which is defined by the IEEE802.3 ad standard. That is, two devices are connected in parallel through more than two ports of the same type to transmit data at the same time, so as to provide higher bandwidth, better redundancy, and achieve load balancing. Link aggregation technology can not only provide high-speed connections between switches but also provide high-speed channels for the connections between switches and servers. It is important to note that not all types of switches support both technologies.

Method 2: Stack

Stacking refers to combining more than one switch to work together to provide as many ports as possible in a limited space. Multiple switches are stacked to form a stacking unit. There is a parameter of “maximum stackable number” in the performance index of stackable switches, which refers to the maximum number of switches that can be stacked in a stacking unit, and represents the maximum port density that can be provided in a stacking unit.

The concepts of stacking and cascading are both distinct and related. Stacking can be seen as a special form of cascading. The difference between them is that the cascaded switches can be far apart (within the permitted range of the media), while the distances between multiple switches in a stacking unit are very close, generally no more than a few meters; Common ports, while stacking generally use dedicated stacking modules and stacking cables. Generally speaking, switches of different manufacturers and models can be cascaded with each other, but the stacking is different. It must be performed between stackable switches of the same type (at least switches of the same manufacturer); cascading is only between switches. Simple connection, stacking is to use the entire stacking unit as a switch, which not only means the increase of port density but also means the widening of the system bandwidth. At present, mainstream switches on the market can be subdivided into two categories: stackable and non-stackable. Among the switches that claim to be stackable, there are virtual stacks and real stacks. The so-called virtual stack is actually a cascade between switches. Switches are stacked not through dedicated stacking modules and stacking cables, but through  Fast Ethernet ports or  Giga Ethernet ports, which is actually a cascade in disguise. Even so, multiple switches in a virtual stack can already be managed as a single logical device in the network, making network management easy.

Stacking in the true sense should meet the following requirements: dedicated stacking modules and stacking buses are used for stacking without occupying network ports; after multiple switches are stacked, they have sufficient system bandwidth to ensure that each port can still achieve wire-speed switching after stacking; After two switches are stacked, functions such as VLAN are not affected.

There are quite a few stackable switches on the market today that are of virtual stacking type rather than true stacking type. Obviously, real stacking is much higher in performance than virtual stacking, but there are at least two advantages to using virtual stacking: virtual stacking often uses the standard  Fast Ethernet or  Gigabit Ethernet as the stacking bus, which is easy to implement and low cost; The stack port can be used as a common port, which is beneficial to protect user investment. Using standard  Fast Ethernet or  Gigabit Ethernet ports to achieve virtual stacking can greatly extend the range of stacking so that stacking is no longer limited to a cabinet.

Stacking can greatly increase switch port density and performance. Stacking units have port densities and performance comparable to larger rack switches at a much lower investment and flexibility than rack switches. This is the advantage of stacking.

Stacking can only be performed between switches that support stacking, and a dedicated stacking cable is used to connect them in a certain connection mode through the stacking interface provided on the switch. The stacking of multiple switches is realized by connecting a multi-port stacking mother module that provides backplane bus bandwidth with a single-port stacking sub-module and inserting different switches to realize the stacking of switches.

All switches in the stack can be managed as a whole switch, that is, all switches in the stack can be regarded as one switch in terms of topology. Switches that are stacked together can be managed as a single switch. The switch stacking technology uses a special management module and stack connection cable. The advantage of this is that, on the one hand, the user ports are increased, and a wider broadband link can be established between the switches so that the actual bandwidth of each user is reduced. Possibly wider (only if not all ports are in use). On the other hand, multiple switches can be used as a large switch, which is convenient for unified management.

Method 3: Cluster

Cluster is to manage multiple interconnected (cascaded or stacked) switches as a logical device. In a cluster, there is generally only one management switch, called the command switch, which can manage several other switches. In the network, these switches only need to occupy one IP address (only required by the command switch), saving valuable IP addresses. Under the unified management of the command switch, multiple switches in the cluster work together, which greatly reduces the management intensity.

The benefits that cluster technology brings to network management work are beyond doubt. However, to use this technology, it should be noted that different manufacturers have different implementation schemes for clusters. Generally, manufacturers use proprietary protocols to implement clusters. This determines that cluster technology has its limitations. Switches from different manufacturers can be cascaded, but not clustered. Even if the switches of the same manufacturer, only the specified model can realize the cluster.

The three technologies of the cascade, stacking, and clustering of switches are both different and related. Cascading and stacking are the prerequisites for realizing clusters, and clusters are the purpose of cascading and stacking; cascading and stacking are implemented based on hardware; clusters are implemented based on software; cascading and stacking are sometimes very similar (especially cascading and virtual stacking), sometimes very different (cascading and true stacking). With the development of local area network and metropolitan area network, the above three technologies will be more and more widely used.

After reading the above three methods, now you must have understood cascading, stacking, and clustering switches. If you are looking for stackable switches, why not have a look at V-SOL Layer2/3 switches with various performances?

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