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

In large organizations, you usually see a large and complex network of locations, devices, services, and protocols. Managing and troubleshooting these networks can be cumbersome. In addition to the development of technology, the network must also develop. It is often difficult to make changes to complex networks. Cisco defines a three-tier hierarchical model based on its years of experience in network equipment and managing its own network. The model provides a hierarchical and modular method to build a network, which can easily implement, manage, expand and troubleshoot the network.

The model divides the Internet into the following three levels:

Core layer

Convergence layer

Access layer

These layers are logical rather than physical. They have specific functions in the Internet, which are discussed below:

Core layer-this layer is the backbone of the Internet. It is the simplest but most critical layer whose only function is to transfer large amounts of data quickly. It takes data from the distribution layer and sends it back to the aggregation layer after transmission. Speed and fault tolerance are the two main requirements of this layer, because it must transmit a large amount of data, and any failure in this layer will affect every user. Considering the functionality of this layer, the following situations should be avoided at this layer:

Anything that slows down traffic. For example, packet filtering, inter-VLAN routing, etc.

Direct user connection

Direct server connection

Complex service policies

When designing the core, you should keep the following points in mind:

Routing protocols should have a low convergence time.

Network access layer technology should be fast and low latency.

Redundancy should be established at this layer.

Aggregation layer-this layer acts as the interface between the core layer and the access layer. The main function of the aggregation layer is to provide routing, filtering and WAN access, and to determine how packets access the kernel as needed. Path determination is the most important function in the layer. It must choose the fastest way in which the access request can be completed. This layer also serves as an aggregation point for all access layer switches. Therefore, it is usually the best place to apply most policies. The following is usually done on this floor:

Routing between subnets and VLAN and routing assignment between routing protocols

Implementation of security policies, including firewalls, address translation, packet filtering, etc.

Break the broadcast domain

Access layer-this layer is the edge of the network, PC, printers, iPad and other devices connected to the network. Common resources required by users are available at this layer, while requests for access to remote resources are sent to the aggregation layer. This layer is also known as the desktop layer. The following is usually done on this floor:

In addition to the access controls and policies that exist in the distribution layer.

Dynamic configuration mechanism

Break the conflict domain

Ethernet switching and static routin

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