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The pros and cons of Layer2 vs Layer3 switches

NetworkTigers discusses the pros and cons of Layer2 vs Layer3 switches.

Network switches are useful connectivity tools that allow you to make the most of your setup. However, different kinds of switches offer different pros and cons. Should you choose a Layer2 or a Layer3 switch? What is the difference between Layer2 and Layer3? These are crucial questions to answer to equip your network with the right gear for your needs. 

The OSI model, Layer2 and Layer3

The labeling for Layer2 and Layer3 network switches comes from the OSI Model, also known as Open Systems Interconnection. This concept was first laid out in 1984. While today’s internet is based on TCP/IP modeling, understanding OSI is still the key to differentiating between Layer2 and Layer3 switches. It helps explain how a network functions and how to describe different network architectures. 

The OSI model involves seven different layers:

  1. Physical
  2. Data link
  3. Network
  4. Transport
  5. Session
  6. Presentation
  7. Application

The TCP/IP model, on the other hand, involves fewer steps, condensing the OSI model. The steps involved in the TCP/IP model start from a network interface, such as a wireless hub or ethernet cable, and move to network packets, ts such as IP, ICMP, IPSec, or IGMP. From there, data is transported via end-to-end connections and finally reaches its application, encompassing layers five through seven of the OSI model. 

Layer2 and Layer3 switches are named for the second and third layers of the OSI model. A Layer2 switch works on the data link level. Layer3 works within both the data link concept, as well as as a network device, like a router.

Layer2 switch: what is it and what does it do best

Each port on a network switch is a separate collision domain. This ensures that data can move smoothly throughout the network without delays. Otherwise, data packet collisions, like those resulting from a singular hub, can occur. A data packet collision happens when two network devices on one segment attempt to send data simultaneously. While a bridge can help divert the issue, network bridges have limited ports. Switches are the elegant fix, as they can inspect incoming traffic and make forwarding decisions, directing data through each of their ports. Because each port is a separate collision domain, no clogs in the system occur. Layer2 switches to keep a MAC address log that allows them to direct traffic as swiftly as possible, avoiding possible collisions through each separate port. 

Layer2 switches work by:

  1. Learning the MAC address of the device
  2. Message forwarding through Unicast and flooding
  3. Filtering data by forwarding a frame through the switch port that has already learned and adapted the MAC address
  4. Maintaining a MAC address table 
  5. Using Spanning Tree Protocol (STP) to avoid looping
  6. Reducing LAN traffic

Because of this, a Layer2 switch is a fast and efficient network device to invest in. This hardware-based solution is a low-cost, low-latency option that moves data at wire speed.

Layer3 switch: what is it and what does it do best

A Layer3 switch can also be called a multi-layer switch, because it performs functionalities along both Layer2 and Layer3 of the OSI model. A Layer3 switch can operate as both a switch and a router by inspecting the MAC address and each additional packet to determine the IP address. In this way, a Layer3 switch has multiple broadcast domains and can implement VLANs. 

Layer3 switches get a bad reputation as the slower option between the two choices. While they involve slower speeds, as they inspect all data packets instead of just MAC addresses, they also can reduce overall network delays by restructuring data flow using VLANs. In this way, a Layer3 switch can still improve overall network speed and usage when multiple outside devices are involved.

Layer2 vs Layer3 switch: which one should I get? 

A Layer2 switch is often a good solution for a smaller business or network. It’s relatively inexpensive and works quickly and efficiently to solve data packet collisions on your network. However, it cannot replace a router; it only works with MAC addresses, not IPs. Devices running through a Layer2 switch are all linked within the same network, with no routing involved. If you need a speedy, single-broadcast domain where all your devices operate within the same network, then a Layer2 switch is probably the right choice.

On the other hand, Layer3 switches offer extended capabilities, with some drawbacks for speed. Because Layer3 switches use IP addresses to link together subnets, more time is required for the device to examine the data packets it absorbs before sending them to the desired destination. By nature, Layer3 switches offer a slightly slower process because they can span multiple networks. If you need to aggregate multiple access points, or span multiple VLANs, you need a Layer3 switch

Gabrielle West
Gabrielle West
Gabrielle West is an experienced tech and travel writer currently based in New York City. Her work has appeared on Ladders, Ultrahuman, and more.

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The pros and cons of Layer2 vs Layer3 switches