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Layer 2 vs Layer 3 Switch: Which One Do You Need?

Updated on Oct 6, 2021 by
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Network switch can access all kinds of terminal devices, set up LANs, and achieve direct communications among all equipment. With the development of the network, different switches are put into application. According to the OSI model, the Layer 2 switch works on the data link layer, while the Layer 3 switch works on the network layer. There comes the question: Should I use a layer 2 or layer 3 switch?

Before that, we need to first understand the definition of OSI models and network switches.

OSI Model and Network Switch: What Are They?

OSI Model:

The Open Systems Interconnection model (OSI model) is a conceptual model from the International Organization for Standardization (ISO) that "provides a common basis for the coordination of standards development for systems interconnection." In the OSI reference model, the communications between systems are split into seven different abstraction layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.

Figure 1: OSI Model

Network Switch:

A network switch (also called switching hub, bridging hub, and, by the IEEE, MAC bridge) is networking hardware that connects devices on a computer network by using packet switching to receive and forward data to the destination device.

A network switch is a multiport network bridge that uses MAC addresses to forward data at the data link layer (layer 2) of the OSI model. Some switches can also forward data at the network layer (layer 3) by additionally incorporating routing functionality. Such switches are commonly known as layer-3 switches or multilayer switches.

 

What is a Layer 2 switch?

Layer 2 switch is a traditional network switch port that operates in the network data link layer or the "layer 2" of the OSI model of network connection. Purely operating within the network's hardware layer, these switches forward data packets based on the MAC addresses specified.

Layer 2 switch is highly efficient because there is no modification to the frame required. Encapsulation of the packet changes only when the data packet passes through dissimilar media (such as from Ethernet to FDDI). Layer 2 switch is used for workgroup connectivity and network segmentation (breaking up collision domains).

In short, here is what a Layer 2 switch does:

1. High-speed forwarding: Layer 2 switch can realize fast forwarding of data frames because it does not need to decapsulate and encapsulate the data frames. It only needs to find the port corresponding to the target MAC address in the address table, and then send the data frame out of the port.

2. Isolate conflict domains: Layer 2 switch can treat each port as an independent conflict domain, thereby reducing collisions and retransmissions of data frames and improving network performance.

3. Support VLAN: Layer 2 switch can support the division of virtual LANs (VLANs). By adding VLAN identifiers to data frames, the division and management of different logical networks can be achieved.

 

What is a Layer 3 switch?

Layer 2 and Layer 3 differ mainly in the routing function. A Layer 2 switch works with MAC addresses only and does not care about IP addresses or any items of higher layers. Layer 3 switch, or multilayer switch, can do all the job of a layer 2 switch and additional static and dynamic routing. That means, a Layer 3 switch has both a MAC address table and an IP routing table and handles intra-VLAN communication and packet routing between different VLANs. There is also a layer 2+ (layer 3 Lite) switch that adds only static routing. Other than routing packets, layer 3 switches also include functions that require understanding the IP address information of data entering the switch, such as tagging VLAN traffic based on IP address instead of manually configuring a port. Layer 3 switches are increased in power and security as demanded.

In short, here is what a Layer 3 switch does:

1. Isolated broadcast domain: Layer 3 switch can treat each port as an independent broadcast domain, thereby reducing the impact of broadcast storms on network performance and improving network security.

2. Support routing protocols: Layer 3 switches can support various routing protocols (such as RIP, OSPF, BGP, etc.) to achieve dynamic routing updates and selections with other routers or layer 3 switches, improving network reliability and flexibility.

3. Support policy routing: Layer 3 switch can support policy routing based on source IP address, destination IP address, protocol type, and other conditions, thereby enabling different processing or forwarding of data packets of different types or priorities, improving network efficiency and quality.

when to use Layer 2 switch, Layer 3 switch and router

Figure 2: when to use the Layer 2 switch, Layer 3 switch and router?

What are the differences between Layer 2 and Layer 3 switches?

Following is a comparison of the key differences between Layer 2 and Layer 3 switches:

Item

Layer 2 Switch

Layer 3 Switch

Routing Function

Work with MAC address only

Supports higher routing such as static routing and dynamic routing

Transfer Method

Send “frames” to the destination based on the MAC address

Route packet with the help of the IP address

Transfer Speed

Quite fast as they do not look at the Layer 3 portion of the data packets

Takes time to examine data packets before sending them to their destination

Communication Range

Can communicate within a network only

Can communicate within or outside the network

Broadcast Domain

It has a single broadcast domain

It has multiple broadcast domain

Cost

More cost-effective 

More expensive

 

Summary

This post has explained the differences between Layer 2 and Layer 3 Switch. The comparison of their functions is also made, in the hope of solving the problem of deciding between these devices. In network systems, Layer 2 and Layer 3 switches can be selected and combined according to different needs and scenarios to achieve high efficiency and reliability of network communication.

 

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