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As we all know, industrial switches are generally connected in these three ways: cascading, stacking and clustering. However, many friends do not have a comprehensive understanding of these three connection methods. So today we will introduce in detail these three connections and the differences between them!

The cascade technology of switches is generally used to realize the interconnection of multiple switches; the stacking technology is used to form a unit of multiple switches so as to improve the greater port density and higher performance; cluster technology is used to manage multiple switches connected to each other as a logical device, so as to reduce network management costs and simplify management operations.

1. Cascade connection

Cascading can be defined as two or more switches connected to each other in a certain way. Multiple switches can be cascaded in a variety of ways as needed. In larger local area networks such as campus networks, multiple switches generally form a bus, tree or star cascade structure according to their performance and purpose.

Metropolitan area network is an excellent example of switch cascading. At present, local telecommunications departments have built many municipal-level broadband IP man. These metropolitan area networks are generally divided into three levels from top to bottom: core layer, convergence layer, access layer. The core layer generally adopts gigabit Ethernet technology, the convergence layer adopts 1000M/100M Ethernet technology, and the access layer adopts 100M/10M Ethernet technology, which is called "gigabit to building, 100 megabit to floor, 10 megabit to desktop".

The broadband metropolitan area network with this structure is actually made up of many switches at all levels. A number of aggregation switches are connected under the core switch (or router), a number of cell center switches are connected under the aggregation switch, and a number of building switches are connected under the district center switch. the building switch is connected with a number of floor (or unit) switches (or hubs).

Switches are generally cascaded through ordinary user ports, while some switches provide special cascade ports. The only difference between these two ports is that the ordinary port conforms to the MDI standard, while the cascading port (or uplink port) conforms to the MDIX standard. As a result, the connection modes of the two modes are different: when both switches are cascaded through ordinary ports, the inter-port cable is connected by a straight-through cable (Straight Throurh Cable); when and only one of them passes through the cascaded port, a crossover cable (Crossover Cable) is used.

To facilitate cascading, some switches provide a dual-purpose port (MDI or MDIX) that can be set to MDI (MDI is a normal UTP or STP connection) or MDIX (the sending and receiving pairs of connectors are inverted internally, which makes different devices (such as hub-hub or collector-switch) You can use conventional UTP or STP cables to achieve back-to-back cascading. Furthermore, all or part of the ports on some switches have MDI/MDIX self-calibration function, which can automatically distinguish the type of network cable, which is more convenient for cascading.

When cascading, it should be noted that, in principle, any manufacturer and any type of Ethernet switch can be cascaded, and a single page does not rule out that the two switches cannot be cascaded in some special cases. There is a limit to the number of layers of cascading between switches. The most fundamental principle for successful cascading is that the distance between any two sites cannot exceed the maximum span of the media segment. When multiple switches are cascaded, they should all support spanning Tree Protocol, which should not only prevent loops in the network, but also allow redundant links to exist.

When cascading, every effort should be made to ensure that the trunk links between switches have sufficient bandwidth, so full-duplex technology and link aggregation technology can be adopted. After the switch port adopts full-duplex technology, not only the throughput of the corresponding port is doubled, but also the ultimate distance between switches is greatly increased, which makes it possible to cascade multiple switches with remote distribution and long distance. Link aggregation, also known as port aggregation, port bundling, link expansion combination, is defined by the IEEE802.3ad standard. That is, two devices are connected through more than two ports of the same type, and data is transmitted at the same time, in order to provide higher bandwidth, better redundancy and load balancing.

It is important to note that not all types of switches support both technologies.

two。 Stacking

Stacking refers to the combination of more than one switch to work together to provide as many ports as possible in limited space.

Multiple switches are stacked to form a stack unit, and one of the stackable switch performance metrics is a "maximum number of stackable switches", which refers to the maximum number of switches that can be stacked in a stack unit. represents the maximum port density that can be provided in a stack unit.

The concepts of stacking and cascading are both different and related. Stacking can be seen as a special case of cascading. The difference between them is that cascaded switches can be far apart (within the range of media permission), while multiple switches in a stacking unit are very close, usually no more than a few meters, and cascading generally uses ordinary ports. stacking generally uses dedicated stacking modules and stacking cables. Generally speaking, different manufacturers and different models of switches can be cascaded with each other, but stacking is different, it must be carried out between stackable switches of the same type; cascading is only a simple connection between switches. Stacking uses the entire stack unit as a switch, which means not only an increase in port density, but also a widening of the system bandwidth.

At present, the mainstream switches in the market can be subdivided into stackable and non-stackable switches. Among the switches that claim to be stackable, there are virtual stacking and real stacking. The so-called virtual stack is actually a cascade between switches. The switch is not stacked through dedicated stacking modules and stacking cables, but through Fast Ethernet ports or Giga Ethernet ports, which is actually a disguised cascade. Even so, the virtual stack of multiple switches can already be managed as a logical device in the network, making network management easier. In the real sense, stacking needs to be met: using dedicated stacking module and stacking bus to stack without occupying network ports, and having sufficient system bandwidth after multiple switches are stacked, so as to ensure that each port can still achieve line-speed switching after stacking; after multiple switches are stacked, functions such as VLAN will not be affected.

At present, there are a considerable number of stackable switches on the market that belong to the virtual stack type rather than the real stack type. Obviously, real stacking has much higher performance than virtual stacking, but virtual stacking has at least two advantages: virtual stacking often uses standard Fast Ethernet or Giga Ethernet as the stacking bus, which is easy to implement and low cost; stack ports can be used as ordinary ports to protect user investment. Using standard Fast Ethernet or Giga Ethernet ports to achieve virtual stacking can greatly extend the scope of the stack, so that the stack is no longer limited to one cabinet.

Stacking can greatly improve switch port density and performance. Stacking units have port density and performance comparable to large rack switches, but the investment is much cheaper and much more flexible to implement than rack switches. This is the advantage of stacking.

Rack switches can be said to be the product of the development of stacking to a higher stage. Rack switch generally belongs to the switch above the department level, it has multiple slots, high port density, supports a variety of network types, good scalability, strong processing capacity, but expensive.

3. Cluster

The so-called cluster is to manage multiple switches that are connected (cascaded or stacked) as one logical device. For the urgent masses, there is generally only one switch that plays a management role, which becomes a command switch, and it can manage several other switches. In the network, these switches only need to occupy one IP address, which saves the IP address. Under the unified management of the command switch, multiple switches in the cluster work together, which greatly reduces the management intensity.

For example, the administrator can upgrade the version of all the switches in the cluster simply by ordering the switch.

There is no doubt about the benefits that cluster technology brings to network management. However, in order to use this technology, it should be noted that different manufacturers have different implementation schemes for clusters, and 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 switch of the same manufacturer, only the specified model can realize the cluster.

For more product-level specifications, you can consult in the product center or contact customer service personnel. Huashu Communication, 15 years of professional industrial switches, optical fiber transceivers, network extenders, Internet of things gateways, 4G routers, protocol converter manufacturers, independent research and development brand, welcome to come to understand and exchange.

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