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

Updated on Oct 6, 2021 by
578.9k

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 (OSI) model is a conceptual framework that divides network communication functions into seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.

Sending data over a network is a complex process that requires collaboration among various hardware and software technologies, transcending geographical and political boundaries. The OSI data model provides a universal language for computer networks, enabling different technologies to communicate using standard protocols or communication rules. Each technology within a specific layer must provide specific functionality and perform designated tasks to operate within the network. Higher-level technologies benefit from abstraction as they can utilize lower-level technologies without worrying about the underlying implementation details.

Advantages of OSI Model:

  • Hardware and software determination

  • Process understanding and communication

  • Efficient troubleshooting

  • Open interoperability

  • Clear product functionality communication

OSI Model

                                                                                            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?

A Layer 2 switch, operating in the network data link layer of the OSI model, efficiently forwards data packets based on MAC addresses. It operates within the hardware layer, eliminating the need for frame modification. Layer 2 switches are commonly used for workgroup connectivity and network segmentation, enhancing performance and reducing collision domains.

Key functionalities of a Layer 2 switch include:

1. High-speed forwarding: These switches achieve fast data frame forwarding by referencing the address table to find the port associated with the destination MAC address. This eliminates the need for decapsulation and encapsulation of data frames.

2. Collision domain isolation: Each port on a Layer 2 switch is treated as an independent collision domain, reducing collisions and retransmissions of data frames, thereby improving network performance.

3. VLAN support: Layer 2 switches enable the creation and management of virtual LANs (VLANs). By adding VLAN identifiers to data frames, different logical networks can be divided and controlled effectively.

What Is a Layer 3 Switch?

Layer 2 and Layer 3 switches differ primarily in their routing capabilities. A Layer 2 switch operates solely based on MAC addresses, disregarding IP addresses and higher layer elements. On the other hand, a Layer 3 switch, or multilayer switch, performs the functions of a Layer 2 switch and adds static and dynamic routing capabilities. This means that a Layer 3 switch maintains both MAC address and IP routing tables, facilitating intra-VLAN communication and packet routing across different VLANs. Additionally, there are Layer 2+ (Layer 3 Lite) switches that offer static routing exclusively. Layer 3 switches not only route packets but also provide advanced features like VLAN traffic tagging based on IP addresses, enhancing power, security, and network management capabilities.

Key functionalities of a Layer 3 switch include:

1. Isolated broadcast domains: Each port on a Layer 3 switch functions as an independent broadcast domain, minimizing the impact of broadcast storms on network performance and bolstering network security.

2. Routing protocol support: Layer 3 switches can accommodate various routing protocols (such as RIP, OSPF, BGP, etc.), enabling dynamic routing updates and exchanges with other routers or Layer 3 switches. This enhances network reliability and flexibility.

3. Policy routing support: Layer 3 switches offer policy routing capabilities based on source IP addresses, destination IP addresses, protocol types, and other conditions. This allows for differentiated processing or forwarding of data packets based on their types or priorities, optimizing network efficiency and quality.

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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

How to Choose the Suitable Switches for Your Network Need

When choosing between a Layer 2 switch and a Layer 3 switch, consider the following:

For Layer 2 Switch:

1. Network Size: Suitable for small to medium-sized networks with high-speed connectivity requirements within the same network segment.

2. Network Segmentation: Helps reduce congestion and improve performance by dividing the network into smaller domains in a LAN setting.

3. Cost-Effectiveness: Generally less expensive due to limited functionality.

4. Simple Subnet Networks: Adequate for single subnet networks with low traffic volumes.

For Layer 3 Switch:

1. Advanced Routing: Required for networks needing inter-VLAN routing, QoS, and security features.

2. Multiple VLANs: Enables routing between VLANs, making it ideal for large organizations with complex network setups.

3. Network Scalability: Offers greater scalability by handling routing between multiple segments, preventing congestion and allowing for complex traffic patterns.

4. Future Expansion: Recommended for networks with anticipated growth, providing advanced routing capabilities.

When to use the Layer 2 switch, Layer 3 switch and router?

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

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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