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Layer 2 vs Layer 3 Switch vs Router: Differences

AuthorDerek

Date11/18/2022

Layer 3 switches are devices that operate in the third layer of the OSI model. What is the difference between the Layer 2 and Layer 3 switch, and what about the difference between the Layer 3 switch and router? What network environments do these devices applicable for? Let’s find the answers in the following post.

Layer 2 and Layer 3 Switching Technology

Layer 3 switching technology, also known as IP switching technology, is proposed after layer 2 switching technology. It operates in the third layer of the OSI network model. The traditional router also operates in the third layer. It can handle a large number of packets across the IP subnet, but its forwarding efficiency is relatively low. However, the third layer switching technology implements high-speed forwarding in the third layer of the OSI model, which greatly improves efficiency.

 

The emergence of Layer 3 switching technology solves the problem that subnets must rely on routers for management and also solves the bottleneck problem of traditional low-speed routers, access between subnets and subnets, and external access.

Layer 2 and Layer 3 Switch Explained

What is a Layer 2 switch? Layer 2 switch is the traditional switch device, and it operates on the second Layer of the OSI model, that is, the data link Layer. Layer 2 switches use MAC addresses to broadcast, and each host will receive the broadcast information. The hosts will check whether the MAC address is the same as their own MAC address. If the MAC address is the same as their own, they will receive the information, if not, they will discard it. 

 

What is a Layer 3 switch? It is a device operated on the third Layer of the OSI model (learn more about the OSI model), that is Network Layer. Different from the L2 switch, the L3 switch uses logical addresses to forward data packets at a high speed. To put it simply, Layer 3 switches are "Layer 2 switching + Layer 3 forwarding". There is a route cache table in a Layer 3 switch. During the data forwarding, the L3 switch will check the route cache table first. If there are corresponding records in the cache table, Layer 2 will fast-forward according to the cache records. If there are no corresponding records, the L3 switch will send the packet to the routing processor for processing, and then forward. In the meantime, the cache table will record the information of the packet. If data is sent to the same destination again, the L3 switch will directly send the data at Layer 2 based on the cache table, thus simplifying the routing process. 

 

The Layer 3 switch is a device with a Layer 3 switching function, and it can be seen as a layer 2 switch but has a layer 3 routing function. Since only Layer 3 processing is required in the routing process, and most data is forwarded through Layer 2 switching, Layer 3 switches are fast, close to the speed of Layer 2 switches, and much cheaper than the same routers. 

 

The came out of Layer 3 switch solves the problem that the Layer 2 switching technology cannot handle the data exchange between different IP subnets, and also solves the network bottleneck problem caused by the low speed and complexity of the traditional router, which is particularly suitable for building a high-speed LAN network.

 

Layer 2 vs Layer 3 Switch: What Are the Differences

After explaining what are L2 and L3 switches, in this part, the main differences between Layer 2 and Layer 3 are concluded in the following chart:

 

L2 vs L3 Switch

 

Layer 2 Switch

Layer 3 Switch

Operate on the second Layer of OSI (Data Link Layer)

Operate on the third Layer of OSI (Network Layer)

Send packets based on MAC address

Route packets based on IP address

Perform Switching function only

Perform switching and routing functions

Used to reduce LAN traffic

Used to implement VLAN

Applicated in small-sized LAN 

Applicated in large-sized LAN

 

Layer 3 Switch vs Router: Differences

The reason why people are confused about the differences between Layer 3 switches and routers is that Layer 3 switches also have a routing function. To be clear, the Layer 3 switch is not equal to the router. Specifically, the differences between them are as follows.

 

Different main functions. Although both the Layer 3 switch and router have a routing function, the L3 switch is not equal to the router. Layer 3 switch is still a switch device, but it has some basic routing functions. That is to say, it has both switching and routing functions, but its main function is still data switching, while the router only has a routing function.

 

Different Applications. Layer 3 switches are mainly used for simple LAN connections. Therefore, the routing function and the routing path of the Layer 3 switch are much simple than that of a router. Its main purpose in a LAN is to provide a fast data switching function and meet the requirements of frequent data switching in a LAN. The router is different, it is mainly to meet different types of network connections. Although it is also applicable to the connection within a LAN, its routing function is more applicated in the interconnection between different types of networks, such as the connection between LAN and WAN, and the connection between networks with different protocols. In order to connect with various types of networks, it has multiple types of interfaces, while a layer 3 switch generally has only one type of LAN interface.

 

Different processing data ways. Technically, there are obvious differences between routers and Layer 3 switches in packet switching operations. Routers generally use microprocessor-based software routing engines to perform packet switching, while layer 3 switches perform packet switching through hardware.

 

On the whole, the performance of the Layer 3 switch is far better than that of the router, which is very suitable for LAN with frequent data switching; Although the routing function of the router is very powerful, its packet forwarding efficiency is far lower than that of the Layer 3 switch, and it is more applicated in the interconnection of different types of networks, such as the interconnection between the LAN and the Internet. 

 

Summary

To sum up, we could simply consider a Layer 3 switching technology as Layer 2 switching technology plus Layer 3 routing and forwarding technology. The Layer 3 switch is recognized by users for its excellent performance and cost-effectiveness. It is suitable for medium and large LANs. At present, the Layer 3 switch has been widely used in many occasions, such as enterprise networks, campus networks, intelligent community access, etc. QSFPTEK provides a one-stop optical network solution to serve all kinds of businesses, welcome to consult via sales@qsfptek.com.

 

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