What is the difference between Layer 2 and Layer 3 switches?

- Dec 17, 2020-

Layer 2 switches are usually used to connect network devices and client devices in the Ethernet to identify and forward the MAC addresses in data packets. However, with the increase in the diversity of network applications and the development of converged network applications, the application of Layer 3 switches has flourished in data centers, complex enterprise networks, commercial applications and even high-level customer projects.

What are Layer 2 and Layer 3 switches?

In general, the OSI model is divided into seven layers: application layer, presentation layer, session layer, transport layer, network layer, data link layer and physical layer. The two-layer switch works on the second layer (data link layer) of the OSI model, so it is called the two-layer switch. The main functions include physical addressing, error checking, frame sequence and flow control. The three-layer switch is located at the third layer (network layer) and is a device with a three-layer switching function, that is, a two-layer switch with a three-layer routing function, but it is an organic combination of the two, and it is not simply a router device. The hardware and software are superimposed on the LAN switch.

OSI

The difference between Layer 2 and Layer 3 switches

The main difference between Layer 2 and Layer 3 switches is whether they have routing functions. The second layer switch is a data link layer device, which can identify the MAC address information in the data packet, forward it according to the MAC address, and record these MAC addresses and corresponding ports in an internal address table of its own. The three-layer switch is a switch with some router functions. It works on the three layers of the OSI network standard model: the network layer. The purpose is to speed up the data exchange within a large LAN. The routing function it has is also for this purpose. Route once, forward many times. In addition, Layer 3 switches can perform static routing and dynamic routing. This means that the Layer 3 switch has both a MAC address table and an IP routing table, and also handles intra-VLAN communication and packet routing between different VLANs. Switches that only add static routes are called weak Layer 3 switches. In addition to routing data packets, Layer 3 switches also include some functions that need to be able to understand the IP address information of the data entering the switch, such as tagging VLAN traffic based on IP addresses instead of manually configuring ports. The power and safety of the three-layer switch have been improved.

When you are struggling to choose a Layer 2 or Layer 3 switch, you need to consider your network requirements. If your network is a pure Layer 2 network, the Layer 2 switch can meet your needs. In the network structure, this is usually called the access layer. If you need switch aggregation to access multiple switches and perform inter-VLAN routing, you need a layer three switch. This is called the distribution layer in the network topology.

Conclusion

In short, the Layer 2 switch is used in small local area networks. Its fast switching function, multiple access ports and relatively cheap prices provide a very complete solution for small network users. The most important function of the three-layer switch is to speed up the fast forwarding of data within a large local area network, and the addition of the routing function also serves this purpose.