What Is a Core Switch？

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 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 the core switch? Is there only one core switch in a network? What are the differences between the core switch and aggregation/access switch?

What Is a Core Switch?

A core switch is a high-capacity switch generally positioned within the backbone or physical core of a network. A core switch is also regarded as a backbone device that is vital to the successful operation of a network: it serves as the gateway to a wide area network (WAN) or the Internet so that you can use it to connect to servers, your Internet service provider (ISP) via a router, and to aggregate all switches. A core switch needs to be powerful enough and have significant capacity to handle the load sent to it, which means it should always be a fast, full-featured managed switch.

In a public WAN, a core switch interconnects edge switches that are positioned on the edges of related networks. In a local area network (LAN), this switch interconnects work group switches, which are relatively low-capacity switches that are usually positioned in geographic clusters.

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 an 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.

What Should Be Kept in Mind When Using Core Switch?

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

As for the specific type and a number of core switches 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 or Cisco SG300 switch.

The second thing is that a core switch should be fully-managed, which means it should support different methods 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, and 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 an 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.