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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.

Performance

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.

Redundancy

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.

Reliability

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 a Core Switch and Why Do We Need It?

Network switches are categorized into different types according to different principles, such as fixed switch and modular switch based if you can add expansion module to it, and managed switch, smart switch and unmanaged/dumb switch depending on whether you can configure it and the complexity of the configuration. Another way to classify the type of a network switch is by the role it plays in a local area network (LAN). In this case, one switch is considered to be an access switch, an aggregation/distribution switch or a core switch. In small networks we do not see core switch. So many people are having questions about what core switches are. Do you know what is core switch? Is there only one core switch in a network? What are the differences between core switch and aggregation/access switch?

What Is Core Switch?

If we spend some time looking up dictionaries for the meaning of core switch, we will find a definition similar to “A core switch is a high-capacity switch generally positioned within the backbone or physical core of a network. Core switches serve as the gateway to a wide area network (WAN) or the Internet—they provide the final aggregation point for the network and allow multiple aggregation modules to work together (An excerpt from Techpedia).” The definition explains its high-capacity feature, the physical location and its function of connecting multiple aggregation devices in network.

What Are the Differences Between Core Switch and Other Switches?

The biggest difference between core switch and other switches is that, core switch is required to always be fast, highly available and fault tolerant since it connects all the aggregation switches. Therefore, a core switch should be a fully-managed switch. But if it is a switch not used in the core layer, it can be a smart switch or an unmanaged switch.

Another difference is that, the core switch is not always needed in a LAN while we may often have the aggregation switch and the access switch. Because in small networks that have only a couple of servers and a few clients, there’s no actual demand for a core switch vs aggregation switch. In the scenario where we don’t need the core layer, we often call it a collapsed core or collapsed backbone since the core layer and the aggregation layer are combined.

The third difference is that there’s generally only one (or two for redundancy) core switch used in a small/midsize network, but the aggregation layer and the access layer might have multiple switches. The figure below shows where the core switch locates in a network.

Core switch in the core layer

What Should Be Kept in Mind When Using Core Switch?

The first thing we should keep in mind is that core switch is urgently required in two occasions. One occasion is when the access switches are located in different places and there is a aggregation switch in each place, then we need a core switch to optimize the network. Another occasion is when the number of the access switches connecting to a single aggregation switch exceeds the performance of it, and we need to use multiple aggregation switches in a single location, then the use of core switch can reduce the complexity of the network.

With core switch and without core switch

As for specific type and number of core switch that we should adopt in a network, that depends on the scale and budget of our network, including how many servers, clients or lower layers switches we have. For example, say that a small network has 100 users and has 6 48-port Gigabit aggregation switches, a suitable core switch will be like Juniper EX2200, Cisco SG300, or FS.COM S5800-8TF12S 10GbE switch.

The second thing is that a core switch should be fully-managed, which means it should support different method of management, such as web-based management, command line interface and SNMP management. Also it should have some advanced features like support for IPv6, built-in Quality of Service (QoS) controls, Access Control Lists (ACLs) for network security.

And generally the connections to the core layer should be the highest possible bandwidth. In addition, since the core switch act as the center of a LAN, it should be able to reach any devices in the network, not directly but within the routing table. A core switch is usually connected to the WAN router.

Conclusion

In the design of a network, there might be access layer, aggregation layer and core layer. Though the core layer is not required in smaller networks, it is indispensable in medium/large networks. And the high-capacity core switch plays an important role in delivering frames/packets as fast as possible in the center of the network. Its contribution can not be underestimated especially in networks where speed, scalability and reliability are key to users.

Related Article: 48-Port 10GE Switch Selection: What Is the Right Choice?
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