Introduction to Layer 2 and Layer 3 Switches

Layer 2 switches work at the second layer (datalink layer) of the OSI model, hence they are called Layer 2 switches. When a Layer 2 switch receives a data packet, it identifies the MAC address (physical address) information in the packet, forwards it based on the MAC address, and records these MAC addresses along with their corresponding ports in its internal address table.

A Layer 3 switch enables multiple VLANs within an enterprise network to communicate with each other. Layer 3 switching technology implements high-speed packet forwarding at the third layer (network layer) of the network model, allowing for both network routing functionality and optimal network performance based on different network conditions.

Application scenarios and problem-solving:
Layer 2 switches are used for small-scale local area networks, such as small hotels, small businesses in security monitoring, catering, KTV, and small hotels. In a small local area network, there are fewer terminals, and all devices are in the same subnet without the need for inter-subnet (VLAN) communication. In this case, a Layer 2 switch can meet the requirements. For example, in a small restaurant with a peak capacity of 50 people, both terminals and devices can be placed in the same subnet, and a Layer 2 switch can meet the requirements.

Layer 3 switches are primarily used to solve the intercommunication problem between multiple VLANs (Virtual Local Area Networks) in large-scale networks. For example, in an enterprise that is divided into smaller LANs (VLANs) based on departments, the general manager needs to access various departments due to business requirements. This will result in a large number of inter-VLAN accesses, which can be achieved using a Layer 3 switch.

The problem is how to solve it:
Layer 2 switches only need to handle the MAC addresses of data packets, and data exchange is achieved through hardware, so their speed is quite fast. However, they cannot handle data exchange between different network segments. Traditional routers can handle a large number of packets that cross network segments, but their forwarding efficiency is lower than that of Layer 2 switches. Therefore, in order to take advantage of the high forwarding efficiency of Layer 2 switches and handle Layer 3 IP packets, Layer 3 switching technology was born. In simple terms, Layer 3 switching technology is a combination of Layer 2 switching technology and Layer 3 forwarding technology.