Application mechanism of layer-3 switches and their high cost effectiveness

Layer-3 switches use a hardware exchange mechanism to implement the IP routing function, which greatly improves the running efficiency of the entire network and solves the problem of traditional router software routing speed. To describe the role of a layer-3 Switch in many network devices, it is not described as a "mainstay. In campus networks and urban education networks, three-layer switches are available in backbone networks, man backbone networks, and aggregation layers. In particular, three-layer switches must be used for core backbone networks, otherwise, thousands of computers on the entire network will be deployed in a sub-network, which is not only insecure, but also unable to isolate broadcast storms due to the inability to divide broadcast domains.

Although traditional routers can be used to isolate broadcasts, their performance is not guaranteed. The performance of a layer-3 switch is very high. It provides both layer-3 routing and layer-2 switching network speed. Layer-2 switching is based on MAC addressing, while layer-3 switching is based on forwarding traffic of layer-3 addresses. In addition to the necessary routing decision processes, most data forwarding processes are handled by layer-2 switching, this improves the efficiency of packet forwarding.

A layer-3 Switch uses a hardware exchange mechanism to implement the IP routing function. Its Optimized Routing software improves the routing efficiency and solves the routing speed problem of the traditional router software. Therefore, it can be said that layer-3 switches have "vro functions and vswitch performance ".

Layer-3 switching is indispensable for connecting subnets

If the number of computers on the same network exceeds a certain number, usually around 200, depending on the communication protocol), it is likely that the network transmission efficiency will be low due to a large number of broadcasts on the network. To avoid a broadcast storm caused by broadcasting on a large vswitch, You can further divide it into multiple virtual network VLANs ). However, this will cause a problem: Communication Between VLANs must be implemented through routers. However, traditional routers cannot perform communication tasks between VLANs, because the Routing Capability of traditional routers is too weak compared with the network traffic of LAN.

In addition, the price of a gigabit router is unacceptable. If you use a layer-3 Switch to connect to different subnets or VLANs through a gigabit or 10-Gigabit port, after Dividing subnets economically, subnets must rely on routers for communication. Therefore, layer-3 switches are ideal devices for connecting subnets.

Advantages of using a layer-3 Switch:

In addition to excellent performance, layer-3 switches have some features that traditional layer-2 switches do not have. These features can bring many benefits to the Construction of Campus Networks and urban education networks, as listed below.

1. high scalability

When a layer-3 switch is connected to multiple subnets, The subnet only establishes a logical connection with the layer-3 Switch module. It does not need to add ports as traditional external routers do, this protects users' investment in Campus Networks and urban education networks. And meet the requirements of the school 3 ~ 5 years of rapid growth in network applications.

2. High Cost Effectiveness

A layer-3 switch can connect to a large network and can basically replace some traditional routers, but the price is close to that of a layer-2 switch. Currently, the price of a M L3 switch is only tens of thousands, which is similar to that of a high-end L2 Switch.

3. built-in security mechanism

Like a common router, a layer-3 Switch has the access list function to implement one-way or two-way communication between different VLANs. If you set it in the access list, you can restrict users to access specific IP addresses, so that the school can prohibit students from accessing unhealthy sites. The access list can be used not only to prohibit internal users from accessing certain sites, but also to prevent illegal users outside the campus network and the city education network from accessing the network resources inside the campus network and the city education network, thus improving network security.

4. Suitable for multimedia transmission

CERNET often needs to transmit multimedia information, which is a special feature of CERNET. A layer-3 Switch has the QoS service quality control function, which can allocate different bandwidths to different applications. For example, when video streams are transmitted on campus networks and urban education networks, a certain amount of dedicated bandwidth can be reserved for video transmission, which is equivalent to a dedicated channel opened in the network, other applications cannot use the reserved bandwidth, so they can ensure the stability of video stream transmission. The common layer-2 switch does not have this feature. Therefore, when video data is transmitted, the video jitter may occur.

In addition, apsaravideo for VOD is also a frequently used service in CERNET. However, because some VOD systems use broadcast for transmission, broadcast packets cannot implement cross-network segments, so VOD cannot implement cross-network segments, although cross-network segments can be implemented, the number of simultaneous connections is very small. Generally, dozens of connections occupy all the bandwidth. The layer-3 Switch has the multicast function. VOD data packets are sent to subnets in the form of multicast, which not only implements cross-network segment transmission, but also ensures VOD performance.

5. Billing

In campus networks of Colleges and Universities and urban education networks in some regions, there may be a need for billing. Because layer-3 switches can identify IP address information in data packets, they can count the data traffic of computers on the network, you can pay by traffic, or count the time when the computer is connected to the network, and charge by time. However, it is difficult for common L2 switches to achieve both. At present, the National Construction of Campus Networks, urban education network boom, I believe that layer-3 switches with its excellent performance, moderate price, will certainly play a significant role in this boom.