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

Three-tier network structure:

The three-layer network structure is a three-layer network with a hierarchical architecture. The three-tier network architecture adopts hierarchical model design, that is, the complex network design is divided into several levels, each of which focuses on some specific functions, so that a large complex problem can be turned into many simple small problems. The network designed by the three-tier network architecture has three layers: the core layer (the high-speed switching backbone of the network), the aggregation layer (providing policy-based connectivity), and the access layer (connecting workstations to the network).

Core layer: the core layer is the high-speed switching backbone of the network, which plays a vital role in the connectivity of the whole network. The core layer should have the following characteristics: reliability, efficiency, redundancy, fault tolerance, manageability, adaptability, low latency and so on. In the core layer, high-bandwidth gigabit switches should be used. Because the core layer is the hub of the network, it is of great importance. It is very necessary for core layer devices to use dual-computer redundant hot backup, and load balancing function can also be used to improve network performance. The control function of the network is best implemented on the backbone layer as little as possible. The core layer has always been regarded as the ultimate receiver and aggregator of all traffic, so the design of the core layer and network equipment are very strict. Core layer equipment will account for a major part of the investment.

Aggregation layer: the aggregation layer is the "intermediary" between the network access layer and the core layer, that is, the convergence is done before the workstation is connected to the core layer, in order to reduce the load of the core layer equipment. The aggregation layer must be able to handle all traffic from access layer devices and provide uplinks to the core layer, so aggregation layer switches require higher performance, fewer interfaces and higher switching rates than access layer switches. The aggregation layer has many functions, such as policy enforcement, security, workgroup access, routing between virtual local area networks (VLAN), source address or destination address filtering and so on. In the aggregation layer, switches supporting layer 3 switching technology and VLAN should be used to achieve the purpose of network isolation and segmentation.

Access layer: the part of the network that connects or accesses the network directly to the user is called the access layer. The purpose of the access layer is to allow end users to connect to the network, so the access layer switch has the characteristics of low cost and high port density. We advocate the use of equipment with high performance-to-price ratio in the design of the access layer. The access layer is the interface between the end user and the network, it should provide plug and play features, and it should be very easy to use and maintain, while considering the port density.

The access layer provides users with the ability to access the application system in the local network segment, mainly to solve the needs of mutual visits between neighboring users, and to provide sufficient bandwidth for these visits. The access layer should also be properly responsible for some user management functions (such as address authentication, user authentication, billing management, etc.), as well as user information collection (such as user IP address, MAC address, access log, etc.).

In order to facilitate management and improve network performance, large and medium-sized networks should be designed according to the standard three-tier structure. However, for the environment with small network size and short networking distance, the "shrinking core" design can be adopted. Ignoring the aggregation layer, the core layer devices can be directly connected to the access layer, which can save part of the aggregation layer costs to some extent, reduce the maintenance burden, and make it easier to monitor the network status.

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