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Many novices are not very clear about how to understand the layer 3 switch. in order to help you solve this problem, the following editor will explain it in detail. People with this need can come and learn. I hope you can get something.

Layer 3 switch

Layer 3 switch is a switch with some router functions. the most important purpose of layer 3 switch is to speed up the data exchange within a large local area network, and its routing function is also for this purpose, which can be routed once and forwarded multiple times. The regular process such as packet forwarding is realized by hardware at a high speed, while the functions such as routing information update, routing table maintenance, routing calculation and routing determination are realized by software.

Application background

For the consideration of security and convenient management, mainly in order to reduce the harm of broadcast storm, large-scale local area networks must be divided into small ones according to functional or regional factors, which makes VLAN technology widely used in the network, and the communication between different VLAN has to be forwarded through routers, with the continuous increase of mutual visits between networks. Simply using routers to achieve inter-network access, not only because the number of ports is limited, but also the routing speed is slow, which limits the scale and access speed of the network. Based on this situation, the layer 3 switch arises at the historic moment. The layer 3 switch is designed for IP. The interface type is simple, and it has strong layer 2 packet processing ability, so it is very suitable for data routing and switching in large local area networks. It can not only replace or partially complete the functions of traditional routers in the third layer of the protocol, but also has almost the speed of layer 2 switching, and the price is relatively cheap.

In the enterprise network and teaching network, the layer 3 switch is generally used in the core layer of the network, using the gigabit port or 100 megabit port on the layer 3 switch to connect different subnets or VLAN. However, we should be soberly aware that the most important purpose of the emergence of layer 3 switches is to speed up the data exchange within a large local area network, and most of the routing functions are carried out around this purpose, so its routing function is not as strong as professional routers of the same level. After all, there are still many deficiencies in security and protocol support, which can not completely replace the work of routers.

In the process of practical application, the typical practice is: the interconnection of each subnet in the same local area network and the routing between the VLAN in the local area network, using the three-layer switch to replace the router, and only when the interconnection between the local area network and the public network wants to achieve cross-regional network access, only through the professional router.

Working principle of layer 3 switch

Layer 3 switching technology is layer 2 switching technology + layer 3 forwarding technology. The traditional switching technology operates in the data link layer, the second layer of the OSI network standard model, while the three-layer switching technology realizes the high-speed forwarding of data packets in the third layer of the network model. The application of layer 3 switching technology can not only achieve the function of network routing, but also achieve the optimal network performance according to different network conditions.

Why use a layer 3 switch?

1. The backbone of the network needs three layers of switching.

It is not too much to describe the role of layer 3 switches in many network devices as a "mainstay". In the campus network and metropolitan education network, there are opportunities for layer 3 switches from backbone network, metropolitan area network backbone and aggregation layer, especially the core backbone network must use layer 3 switches, otherwise thousands of computers in the whole network are in a subnet, not only there is no security to speak of, but also because the broadcast domain can not be divided and broadcast storm can not be isolated.

If the traditional router is used, although the broadcast can be isolated, the performance can not be guaranteed. The performance of layer 3 switch is very high, which not only has the function of layer 3 routing, but also has the network speed of layer 2 switching. Layer 2 switching is based on MAC addressing, while layer 3 switching is forwarding traffic based on layer 3 addresses. In addition to the necessary routing process, most of the data forwarding process is handled by layer 2 switching, which improves the efficiency of packet forwarding.

The layer 3 switch realizes the routing function of IP by using hardware switching mechanism, and its optimized routing software improves the efficiency of the routing process and solves the speed problem of traditional router software routing. Therefore, it can be said that the layer 3 switch has the function of the router and the performance of the switch.

2. Layer 3 switching is necessary to connect subnets.

If there are more than a certain number of computers on the same network (usually about 200, depending on the communication protocol), the network transmission efficiency is likely to be inefficient because of a large number of broadcasts on the network. In order to avoid the broadcast storm caused by broadcasting on large switches, it can be further divided into multiple virtual networks (VLAN). But doing so will lead to a problem: communication between VLAN must be achieved through the router. However, the traditional router is also not competent for the communication between VLAN, because the routing ability of the traditional ordinary router is too weak compared with the network traffic of the local area network.

And the price of gigabit routers is also very difficult to accept. If the gigabit port or 100 megabit port on the layer 3 switch is used to connect different subnets or VLAN, it economically solves the problem that the subnets must rely on the router to communicate after subnetting, so the layer 3 switch is an ideal device for connecting subnets.

Benefits of using layer 3 switches:

In addition to excellent performance, layer 3 switches also have some characteristics that traditional layer 2 switches do not have, which can bring many benefits to the construction of campus network and metro education network, as listed below.

1. High scalability

When the layer 3 switch connects multiple subnets, the subnet only establishes a logical connection with the layer 3 switching module, unlike the traditional external router, which needs to increase the port, thus protecting the user's investment in the campus network and metro education network. And meet the needs of the rapid growth of network applications in schools for 3 ~ 5 years.

2. High performance / price ratio

Layer 3 switches have the ability to connect to large networks, and their functions can basically replace some traditional routers, but the price is close to that of layer 2 switches. At present, the price of a 100 trillion layer 3 switch is only tens of thousands of yuan, which is similar to that of a high-end layer 2 switch.

3. Built-in security mechanism

Like ordinary routers, layer 3 switch can have the function of access list and can realize one-way or two-way communication between different VLAN. If you set it in the access list, you can restrict users from accessing specific IP addresses, so that the school can prohibit students from visiting unhealthy sites.

Access list can not only be used to prohibit internal users from visiting some sites, but also can be used to prevent illegal users outside the campus network and metro education network from accessing the network resources within the campus network and metro education network, so as to improve the security of the network.

4. Suitable for multimedia transmission

The education network often needs to transmit multimedia information, which is a feature of the education network. Layer 3 switch has the control function of QoS (quality of Service), which can allocate different bandwidth to different applications.

For example, when video stream is transmitted in campus network and metro education network, a certain amount of dedicated bandwidth can be reserved for video transmission, which is equivalent to opening up a special channel in the network, and other applications can not occupy these reserved bandwidth. therefore, it can ensure the stability of video stream transmission. The ordinary layer 2 switch does not have this characteristic, so the video jitter will occur when transmitting video data.

In addition, video-on-demand (VOD) is also a frequently used service in education network. However, because some video-on-demand systems use broadcasting to transmit, and broadcast packets cannot cross network segments, VOD cannot achieve cross-network segments; if VOD is implemented in the form of unicast, although it can achieve cross-network segments, the number of simultaneous connections supported is very small, and generally dozens of connections occupy all the bandwidth. The layer 3 switch has the function of multicast, and the packets of VOD are sent to each subnet in the form of multicast, which not only realizes the transmission across network segments, but also ensures the performance of VOD.

5. Billing function

In the campus network of colleges and universities and the metro education network in some areas, there is likely to be a demand for billing, because the layer 3 switch can identify the IP address information in the data packet, so it can count the data flow of computers in the network, which can be charged according to the flow, and can also count the time the computer is connected to the network. The ordinary layer 2 switch is difficult to achieve these two points at the same time.

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