A network switch, or commonly known as a "switch," is an active network device that directs data communication. It enables efficient and secure data transfer between devices such as computers, printers, or servers within the same local area network (LAN). A switch registers the MAC (Media Access Control) addresses, which are the physical addresses of each device, ensuring that the transmitted data frame reaches only the target device. This increases network performance and prevents unnecessary data traffic.

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Operating Principle

A switch operates at the Data Link Layer, which is the second layer of the OSI model. With the first data frame received by the device, it records the MAC address of the data source into its memory. These addresses are stored in the MAC Address Table within the device. The data packet intended for transmission is directed only to the port to which the target device is connected, according to this table. This process enables many devices to exchange data on the network simultaneously without collisions.

Layer 2 and Layer 3 Switches

Switches are classified according to their operating layers:

Layer 2 Switch: Operates only via MAC addresses. It provides communication between devices within the same network segment. These devices are more economical and sufficient for basic switching operations.
Layer 3 Switch: Operates at the third layer of the OSI model, which is the Network Layer. It can perform routing by considering IP address information. This allows for inter-VLAN transitions or data flow between different network segments.

Layer 3 switches are preferred in large and complex network structures because they also possess router features.

Forwarding Methods

Switches can use one of three basic forwarding methods before transmitting data frames to ports:

Cut-through: Data is transmitted immediately after only the part of the frame containing the destination MAC address is read. No error checking is performed. Latency is low, but corrupted data can be propagated.
Store-and-forward: The entire frame is received, and after error checking (e.g., CRC) is performed, the data is transmitted. Latency can be longer, but secure transmission is ensured through error checking.
Fragment-free: Data is transmitted after the first 64 bytes of the data frame are received. It is a balanced method in terms of both speed and error checking.

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Types of Switches

Switches are classified into different types according to their roles in the network structure:

Backbone Switch: Located at the center of large networks. It has very high bandwidth and data transfer capacity.
Core Switch: A device at the heart of the network that connects distribution switches. Similar to a backbone switch, it is high-performance.
Edge Switch: The device to which end-users (PC, printer, etc.) are directly connected.
Ethernet Switch: The most common type, operating based on Ethernet frames.
Layer 3 Switch: Advanced devices that also support IP-based routing operations.

Management Features and Use Cases

Switches are broadly divided into two main groups: "manageable" and "unmanaged":

Home users or small offices typically use unmanaged switches. They operate directly without requiring any configuration.
Manageable switches, on the other hand, can be configured via a web interface, command line, or management protocols like SNMP. Through these devices, VLAN definitions can be made, port-based speed limits can be applied, or security policies can be implemented.

Impact on Network Performance

The use of switches increases the overall efficiency of the network because:

It creates a dedicated collision domain for each port, thus preventing data collisions.
All ports are by default within the same broadcast domain. However, these domains can be logically separated by configuring VLANs.
Unnecessary data broadcasting is prevented, and bandwidth is used efficiently.

Security and Redundancy Features

Switches used in corporate environments include various security mechanisms. For example:

Port security features can block connections other than specific MAC addresses.
Technologies such as DHCP snooping, IP Source Guard, and Dynamic ARP Inspection offer protection against network spoofing.
Protocols such as Spanning Tree Protocol (STP) prevent loop formation with redundant connections and prevent connection outages.

In systems requiring high availability, redundant switch connections and link aggregation methods are used to increase network resilience.

Network Switch