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What can a network switch do?

Switches connect network segments, enable efficient bandwidth utilisation and provide performance data. Networks have become indispensable in many areas of our lives - whether in a corporate context, for digital communication or a movie night on the sofa at home. A fundamental building block here is the switch, which integrates the corresponding devices and thus supports the sharing of resources.

Definition: Network Switch

A network switch is a device that operates on layer 2 of the OSI model, the so-called data transfer layer. It receives data packets from the devices that are connected to its physical ports and then sends them on - exclusively to the addressed target devices.

In addition, network switches can also be active on the network layer (layer 3), where routing takes place. Switches are a common component of networks based on Ethernet, fibre channel, asynchronous transfer mode (ATM) or Infini-Band, among others. Nowadays, however, switches usually fall back on Ethernet.


Functionality: Network switches

To ensure that data forwarding functions smoothly, the switch remembers the MAC address (Media Access Control) of a device when establishing a connection with it. This is located on the network interface card (NIC) of the device in question, which in turn is connected to the network switch via an Ethernet cable. The MAC address is used by the switch to determine where incoming data packets come from and where outgoing ones are to be sent. Unlike the IP address, which can vary under certain circumstances, the MAC address can be used to identify the physical device behind it at any time.

If one device sends a data packet to another, the switch analyses the header to determine what to do with the data. To do this, it compares the recipient addresses and forwards the data to the target device via the corresponding ports. To avoid collisions between incoming and outgoing traffic, most switches have full duplex functionality, which makes the entire bandwidth of the switch connection available to the data packets. Equipped with routing capabilities, network switches also operate at the network layer. This becomes necessary if the switch is to support virtual local area networks (VLANs) and their subnets.

Hubs vs. network switches

A hub can also connect different devices to share resources. The total set of devices connected to a hub is called a LAN segment. Unlike a network switch, a hub transmits data sent to it to all devices connected to it.

Normally, switches connect LAN segments to each other, which also includes connected hubs. Network switches filter the data traffic and distribute the packets accordingly to the devices in the LAN segment. This allows switches to use their own computing resources as well as network bandwidth more efficiently.

Router vs. network switches

Switches are sometimes confused with routers. Although routers also forward traffic, they do so at a different OSI layer (Layer 3) and for a different purpose, namely connecting networks. The example of LANs and WANs can be used to illustrate the difference between routers and network switches: While devices are connected locally via switches, networks are connected to each other via routers.

Of course, there are also some routers with switch functionalities. The most obvious example is the home WLAN router, which in addition to its broadband connection (via WAN) has Ethernet ports to which you can connect your computer, TV, printer or game console. Other notebooks or smartphones can be connected via the WLAN router - yet switching functions are still available via LAN. In effect, the router is a switch. An additional, separate switch can be used to add both Internet and LAN access for other devices.

Types / kinds: Network switches

Network switches come in different sizes. Which one to use depends on the number of devices to be connected and the required network speed. For the home office, a switch with four to eight ports is usually sufficient; for larger deployments, devices with up to 128 ports are usually used. There is room for switches in many places: smaller devices fit on the desk and many models can be integrated into a rack to be subsequently integrated into a data centre or server farm. The size of these rack-mountable switches typically ranges from 1U to 4U, but larger models are also available if needed.

Another distinguishing criterion for network switches is their network speed. The spectrum here ranges from Fast Ethernet (10/100 Mbit/s), Gigabit Ethernet (10/100/1000 Mbit/s) and 10 Gigabit (10/100/1000/10000 Mbit/s) to 40/100 Gbit/s. The selection of the appropriate speed should be based on the required data throughput.

Last but not least, switches also differ in terms of their functionalities. Essentially, there are three different types of switches:

  • Unmanaged switches: Unmanaged switches are the easiest to use and are pre-configured. However, this plug-and-play characteristic also means that there are few to no customisation options for the user. Although they may have default settings for functions such as QoS (Quality of Service), these cannot be further modified. One argument in favour of unmanaged switches is their relatively low purchase price. In view of these functional deficiencies, unmanaged switches are generally not suitable for use in a corporate context.

  • Managed Switches: Managed switches offer far more functions and features for IT professionals and are therefore the switch type most likely to be found in the business sector. They have command line interfaces for individual configuration and support SNMP agents (Simple Network Management Protocol), which provide information for troubleshooting network problems. In addition, managed switches also support virtual LANs, quality-of-service settings and IP routing. The level of security also increases, as all incoming traffic is protected. Due to these extended functionalities, however, you have to pay considerably more for managed switches than for other switch types.

  • Smart switches: Smart switches are the middle ground between unmanaged and managed switches: They are managed switches whose functional profile is larger than that of unmanaged switches, but does not come close to that of managed switches. Smart switches thus combine a low purchase price with functions that go beyond pure plug-and-play. What they usually lack is support for Telnet access. In addition, they usually have web-based interfaces and may not offer as many functions as "real" managed switches for other configuration options such as VLANs. Smart switches are suitable as a low-cost alternative for smaller networks with limited financial resources or less pronounced feature needs.

Network switch management

The total number of features and functions of a network switch varies depending on the manufacturer - and any additional software supplied. In general, IT professionals can use it to:

  • activate and deactivate certain ports of the switch;

  • Configure duplex and bandwidth settings;

  • set specific QoS levels for specific ports;

  • Enable MAC filtering and other access control features

  • Enable SNMP monitoring of devices;

  • Configure port mirroring to monitor network traffic.

Other areas of application for network switches

In larger networks, switches are often used to outsource data in order to analyse it. This can also play a role in IT security if a switch can be placed between the WAN router and the LAN. This approach helps with intrusion detection, analytics and firewalling. Port mirroring is used: a "mirror image" of the data flowing through the switch is created before it is forwarded to an intrusion detection system or a packet sniffer.

At its core, however, the job of a network switch remains to transfer data quickly and efficiently from computer A to computer B - regardless of whether the computers are across the aisle or on the other side of the world. While the switch is not the only device involved in this process, it is a fundamental part of the network architecture. (fm - networkworld)


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