Shulou(Shulou.com)06/01 Report--

The number of ports of a single switch is limited, which is not enough to meet the needs of network terminal devices to access the network. For this reason, we need to use multiple switches to provide terminal access, and interconnect multiple switches to form a local area network.

There are two main ways of interconnection of switches: Uplink and Stack.

Cascade of switches

Switch cascading is the mainstream connection technology at present. In the three-layer model of network interconnection, the core layer switch, aggregation layer switch and access layer switch are generally cascaded.

The cascading of switches can be divided into three types:

Ordinary port cascade

Two RJ45 interfaces are cascaded: using crossed twisted pair:

Uplink port cascading

Cascade using RJ45 interface and Uplink interface: using straight-through twisted pair

Note: when cascading with two Uplink interfaces, cross twisted pair should be used.

Optical fiber port cascade

When optical fiber ports are cascaded, optical fiber bundles should be crossed

Advantages of cascading

The use of switch cascade mode is conducive to the component structured network, is conducive to comprehensive wiring, easy to understand, easy to install, and can easily realize the access of a large number of ports. Through the unified network management platform, the unified management of the equipment of the whole network can be realized.

The disadvantages of cascading

When the number of cascading layers of the switch is large, there is a larger convergence ratio between the layers, and there will be a larger delay.

The solution is to improve the performance of the switch or reduce the level of cascading

More than a certain number of switches are cascaded, which will eventually lead to a network broadcast storm, resulting in a serious decline in network performance, or even paralysis. Therefore, switches should not be cascaded infinitely.

Stack of switches

The stacking of switches is to connect two or more switches through a stacking module using a stack cable dedicated to the switch.

The idea of switch stacking technology is to embed one switch as a module into another switch.

Note: optical fiber interfaces have no stacking capability and can only be used for cascading

Stacked connection

The stacking module of the switch has two ports: one is the ingress (IN or UP up) and the other is the egress (OUT or DOWN downline).

Connect directly from the OUT port of the stacking module of one switch to the IN port of the stacking module of another switch using a dedicated connection cable provided by the manufacturer (called "stacking cable")

Note: after using stacking, cascading can no longer be used, otherwise a loop will be created, resulting in a network storm

Advantages of stacking

Port density can be expanded by stacking

The number of ports in the stack is the sum of the ports of all the member devices in the stack, and all ports can be used as the ports of a device.

Facilitate the management and operation of users.

Through stacking, users can use a group of switches as a logical object and manage them with only one IP, which reduces the occupation of IP addresses and facilitates management.

Expand the uplink bandwidth

For example, if there are eight switches stacked, the uplink can have eight gigabit ports, and eight gigabit ports form an aggregation port with bandwidth up to 8Gbps.

Disadvantages of stacking

Limited number of stacks

Generally, a maximum of 8 switches are allowed to stack, and stack members are required to be close enough to their location.

The difference between switch cascading and stacking

It is implemented in different ways

The main purpose of stacking and cascading is to increase port density.

Cascading uses twisted pair or optical fiber to connect the switch together through RJ-45 port or optical fiber port. There is no restriction on the brand and model of the switch.

Stacking can only be achieved by using dedicated stacking cables between devices of the same manufacturer and through dedicated stacking modules.

The limit on the number of devices is different

In theory, there is no limit on the number of switch cascades (in fact, when the number of cascades exceeds a certain number, there will be a larger delay)

Switches are stacked, and the equipment of each manufacturer will indicate the maximum number of stacks.

Different performance after connection

Cascading interconnects with other switches through a port on the switch. When there are too many levels of cascading, the cascade will produce a large delay, and the performance of each layer is the worst, and the performance of the last layer is the worst (that is, the maximum delay).

The stack is connected through the backplane of the switch. it is a connection established at the chip level. The delay between any two ports of the switch is equal, that is, the delay of each switch.

Logical attributes are different after connection

Cascaded switches are still logically independent devices, and there is a hierarchical relationship between them.

Multiple switches are stacked together, logically they belong to the same device, and there is no hierarchical relationship.

Connection distance restrictions are different

General cascading can increase the access distance of terminal devices.

The maximum length of stacked cables is only a few meters, and generally the stacked switches are in the same cabinet.

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