What is Core Layer and How to Choose the Right Core Switch?

What is Core Layer?

The Core Layer in networking serves as the backbone of a hierarchical network design, forming a critical component within the three-layer model alongside the Access and Distribution layers. Situated at the center of network architecture, the Core Layer is designed for high-speed, high-capacity packet switching, ensuring swift and efficient transport of data across the entire network.

Unlike the Distribution Layer, the Core Layer typically focuses on rapid data transfer without applying extensive processing or policy-based decision-making. Its primary objective is to facilitate seamless and fast communication between different parts of the network.

Duty of Core Switches

In the enterprise hierarchical network design, the core layer switch is the topside one, which is relied on by the other access and distribution layers. It aggregates all the traffic flows from distribution layer devices and access layer devices, and sometimes core switches need to deal with external traffic from other egresses devices. So it is important for core switches to send large amounts of packets as much as possible. The core layer always consists of high-speed switches and routers optimized for performance and availability.

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Figure 1: Core Switches in the three-tier architecture

Located at the core layer of enterprise networking, a core layer switch functions as a backbone switch for LAN access and centralizes multiple aggregation devices to the core. In these three layers, core switches require most highly in the switch performance. They are usually the most powerful, in terms of forwarding large amounts of data quickly. For most of the cases, core switches manage high-speed connections, such as 10G Ethernet, 40G Ethernet or 100G Ethernet. To ensure high-speed traffic transfer, core switches should not perform any packet manipulation such as Inter-Vlan routing, Access Lists, etc., which are performed by distribution devices.

Note: In small networks, it is often the case to implement a collapsed core layer, combining the core layer and the distribution layer into one as well as the switches. More information about the collapsed core is available in How to Choose the Right Distribution Switch?

Factors to Consider When Choosing Core Switches for Enterprises

Simply put, core layer switches are generally layer 3 switches with high performance, availability, reliability, and scalability. Except for considering the basic specifications like port speed and port types, the following factors should be considered when choosing core switches for an enterprise network design.


The packet forwarding rate and switching capacity matter a lot to the core switch in enterprise networking. Compared with the access layer switches and distribution switches, core switches must provide the highest forwarding rate and switching capacity as much as possible. The concrete forwarding rate largely depends on the number of devices in the network, the core switches can be selected from the bottom to the top based on the distribution layer devices.

For instance, network designers can determine the necessary forwarding rate of core switches by checking and examining the various traffic flow from the access and distribution layers, then identify one or more appropriate core switches for the network.


Core switches pay more attention to redundancy compared with other switches. Since the core layer switches carry much higher workloads than the access switches and distribution switches, they are generally hotter than the switches in the other two layers, the cooling system should be taken into consideration. As often the case, core layer switches are generally equipped with redundant cooling systems to help the switches cooling down while they are running.

The redundant power supply is another feature that should be considered. Imagine that the switches lose power when the networking is running, the whole network would shut down when you are going to perform a hardware replacement. With redundant power supplies, when one supply fails, the other one will instantly start running, ensuring the whole network unaffected by the maintenance.

FS provides switches with hot-swappable fans and power supply modules for better redundancy.


Typically core switches are layer 3 switches, performing both switching and routing functions. Connectivity between a distribution and core switches is accomplished using layer 3 links. Core switches should perform advanced DDoS protection using layer 3 protocols to increase security and reliability. Link aggregation is needed in core switches, ensuring distribution switches delivering network traffic to the core layer as efficiently as possible.

Moreover, fault tolerance is an issue to consider. If a failure occurs in the core layer switches, every user would be affected. Configurations such as access lists and packet filtering should be avoided in case that network traffic would slow down. Fault-tolerant protocols such as VRRP and HSRP is also available to group the devices into a virtual one and ensure the communication reliability in case one physical switch breaks down. What’s more, when there are more than one core switches in some enterprise networks, the core switches need to support functions such as MLAG to ensure the operation of the whole link if a core switch fails.

QoS Capability

QoS is an essential service that can be desired for certain types of network traffic. In today’s enterprises, with the growing amount of data traffic, more and more voice and video data are required. What if network congestion occurs in the enterprise core? The QoS service will make sense.

With the QoS capability, core switches are able to provide different bandwidth to different applications according to their various characteristics. Compared with the traffic that is not so sensitive about time such as E-mail, critical traffic sensitive to time should receive higher QoS guarantees so that more important traffic can pass first, with the high forwarding of data and low package loss guaranteed.

As you can see from the contents above, there are many factors that determine what enterprise core switches are most suitable for your network environment. In addition, you may need a few conversations with the switch vendors and know what specific features and services they can provide so as to make a wise choice.

Related Articles:

How to Choose the Right Access Layer Switch?

How to Choose the Right Core Switch?

What Is Distribution Switch and Why Do We Need It?

We know that in data centers a three-layer hierarchical model contains core layer, aggregation/distribution layer and access layer. In this network topology, corresponding network switch is implemented in different network layer. A core switch is a high-capacity backbone switch, which locates in the topside for WAN access and centralizing multiple aggregations in the core. Thus backbone core layer switch is often a fiber switch for advanced optical link. An access switch or an edge switch is for direct end devices and hierarchy connection. But what is distribution switch? What are the functions of distribution layer switch? And what’s the difference between aggregation switch vs core switch and distribution switch vs router? This article may help.

what is distribution switch and aggregation switch function

What Is Distribution Switch?

A distribution switch is a distribution layer switch, which uplinks to upper layer core switch and links down to the access/edge switch. Simply put, an aggregation switch in between functions a bridge between core layer switch and access layer switch. This is also the reason why we call distribution switch as aggregation switch.

Distribution Switch Functions

Why distribution layer switch is needed in network layers? In general, aggregation switch reacts on multiple switch aggregation and layer 3 routing functionality. It also supports complex policy implementation such as QoS and packet filtering. Highlights, distribution switch employs Access Control Lists (ACL) to offer optimized security policies. This security capability enables aggregation switch to decide which traffic can be permitted for communication. Here we illustrate the necessities of distribution layer switch into details by comparing it to other switches and routers.

  • Distribution Switch vs Access Switch

Usually we employ gigabit Ethernet switch in access layer 2 to run at 1Gb. When traffic driving from a layer 2 switch, the network topology requires a device with layer 3 features to process it to VLANs. Aggregation switch is often a layer 3 switch, so it supports inter-VLAN routing over a layer 2 switch. When multiple access switches among different VLANs are required to be aggregated, a distribution switch can achieve inter-VLAN communication.

  • Core Switch vs Distribution Switch

For core switch vs aggregation switch, one question may come in mind: why not directly connecting access switch to the core switch? An important reason is for convenient network access. When there are dozens of clients spreading over different offices in 5 buildings, we can deploy a distribution layer 10GbE switch in the center of each building to connect multiple access layer gigabit Ethernet switches in different offices. Then the 5 distribution switches can easily link to a 40GbE core switch in data centers. There are cases of combining collapsed distribution and core into one when there are only several severs and end users. We also call such switch as collapsed core or collapsed backbone since distribution layer switch is combined.

using fs 10GbE switch as distribution switch

Figure 1: Deploying FS S5800-48S6Q 10GbE switch with 6 40G QSFP+ uplinks as distribution switch in three-layer hierarchical model.

  • Distribution Switch vs Router

Generally, both a router and distribution layer switch has layer 3 routing functionality. But there is some distinctions. Compared to layer 3 switch/multilayer switch, a router has full layer 3 features and intact routing functionality like Internet Service Provider (ISP) and WAN. A aggregation switch combines layer 2 switching technology with layer 3 routing technology in one hardware. So a layer 3 distribution switch owns edges over router as switch while possessing inter-VLAN routing functionality. Besides, as a router a layer 3 distribution switch can route packets more quickly than a router due to functionality to make cache entry in its fast memory.

deploy layer 3 switch distribution switch over layer 2 switch and routers

Figure 2: Scenarios to deploy layer 3 switch – distribution switch over layer 2 switch and routers.


Despite advanced features of policy-based network connection, distribution layer switch functions aggregation and routing. As an aggregation switch, distribution switch connects multiple access switches and centralizes them to core switch. As a layer 3 switch, distribution switch adds routing functionality to achieve fast and easy inter-VLAN routing communication. As thus distribution switch deployment changes the situation that subnet must relay on router to manage network. And solves the issue of low speed and complexity caused by traditional routers.