What Is Layer 2, Layer 3, and Layer 4 Network Switch?

22. september 2017 at 10:03
With the rapid development of computer networks over the last decade, high-end switching has become one of the most important functions of a network for moving data efficiently and quickly from one place to another. For years, the average network has been dominated by the Layer 2 switch. Now as network complexity increases and applications demand greater functions from the network, Layer 3 and layer 4 network switches are coming out of the data center and high level enterprise settings. This post will introduce them respectively.

What Is A Network Switch?
A network switch (also called switching hub, bridging hub, officially MAC bridge) is a computer networking device that connects devices together on a computer network by using packet switching to receive, process, and forward data to the destination device.

A network switch is a multiport network bridge that uses hardware addresses to process and forward data at the data link layer (layer 2) of the OSI model. Some switches can also process data at the network layer (layer 3) by additionally incorporating routing functionality that most commonly uses IP addresses to perform packet forwarding; such switches are commonly known as layer-3 switches or multilayer switches.
FS 100G Ethernet Switch
Layer 2 Network Switch (The Data-Link Layer)
Layer 2 network switches operate using the data link (MAC) layer addresses. Link-layer, hardware, or MAC-layer addresses identify individual devices. Most hardware devices are permanently assigned this number during the manufacturing process.

The main function of a Layer 2 is to help the traffic from devices within a LAN reach each other. A Layer 2 switch does this by keeping a table of all the MAC addresses it has learned and what physical port they can be found on. The MAC address is something that operates within Layer 2 of the OSI model (what defines how networks operate). Traffic being switched by MAC address is isolated within the LAN those devices are using. When you need traffic to cross between LANs (or VLANs) is when we need a Layer 3 device.

Layer 3 Network Switch (The Network Layer)
Layer 3 ntwork switches use network or IP addresses that identify locations on the network. A location can be a LAN workstation, a location in a computer's memory, or even a different packet of data traveling through a network.

The most common Layer 3 device used in a network is the router. A router is able to look into the Layer 3 portion of traffic passing through it (the source and destination IP addresses) to decide how it should pass that traffic along. Since a router holds information about multiple networks (LAN WAN VLAN) it is also able to pass traffic along between these networks. This is routing. The Layer 3 switch functionally exists somewhere between being a Layer 2 switch and being a Gateway Router. It can be best described by what more it does compared to a Layer 2 switch and what less it does compared to a Gateway Router.

Layer 4 Network Switch (The Transport Layer)
Layer 4 of the OSI Model coordinates communications between systems. Layer 4 switches are capable of identifying which application protocols (HTTP, SNTP, FTP, and so forth) are included with each packet, and they use this information to hand off the packet to the appropriate higher-layer software. A layer 4 network switch enables policy based switching mechanisms that limits different traffic types and prioritizes packets based on their base application importance. A layer 4 switch is among the types of multilayer switches, and is an enhancement to the layer 3 switch that uses hardware based switching techniques.

Layer 4 switches also provide an effective wire-speed security shield for your network because any company- or industry-specific protocols can be confined to only authorized switched ports or users. This security feature is often reinforced with traffic filtering and forwarding features.

Conclusion
As the layers increase in switches, so does the CPU power and processing time (latency) of the switch. The trade-off for more control and capabilities in a higher layer switch is less speed and increased power consumption. Lower layer switches are faster and use less processing power. Therefore, choosing a switch that matches your network needs creates maximum networking efficiency.
 

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