What is Ethernet Switching ?

As you know that most corporate networks use a combination of switches, routers, hubs, and wired & wireless-technologies. In this post, I am revisiting the ethernet switching...

Ethernet switching is about connecting your wired devices, e.g., computers, laptops, servers, printers, etc. to your LAN. Since ethernet switches offer you multiple ports, you can easily establish a faster connectivity and smooth access to multiple devices simultaneously.

You won't find a single corporate network where ethernet switches have not been installed. They are essential to create your networks.
However, ethernet switches are fundamentally very different from routers. Routers connect 'networks' and primarily use only a single LAN and WAN port. Routers connect networks to other networks, most commonly connecting LANs to WANs. Routers are usually placed at the gateway between networks and route data packets along the network. Right?

A network administrator, is expected to provide you fully wired and Wi-Fi connectivity using a right combination of devices, switches and access-points.
Hubs are almost gone, and not seen very frequently in corporate networks. Reason of their decline was that they were there to SHARE the bandwidth equally among ports.

Contrarily, you can use ethernet switches to devote more bandwidth to certain ports without degrading the performance of your network. Experienced IT guys know that when many devices are active on a LAN, ethernet switching provides more robust performance.
You can connect dozens of devices to a network using an Ethernet switch. Ethernet switches allows you to monitor traffic, to control communications among machines, to securely manage access of network users, and rapidly troubleshoot.
You can easily find a right solution (switches) which is best fit for your network, as you can select from wide variety of switches. You can buy plug-n-play switches to feature-rich Gigabit Ethernet switches that actually perform at higher speeds than wireless options.

How Do Ethernet Switches Work?
Let us review the concept of FRAMES first...

A frames is basically a sequence of 'Information.' The format of a Ethernet frame includes a number of different elements such as:
1. Header
This consists of a preamble to enable the receiver to synchronize, a destination address, a source address and a Length / type indication.
2. Payload
This is the actual data to be carried around the local area network by the Ethernet frame.
3. Trailer
This consists of a Frame Check Sequence for error checking.

Normally any ethernet device will only accept frames that are directed to it, but in the case of an ethernet switch, this is not the case, because it handles frames that are intended for OTHER devices. It runs in what is often termed "promiscuous mode."
There have been a number of changes to Ethernet standards, but the basic format of these ethernet frames have remained the same, as described above and shown in the graphic. Why?

Your ethernet data usually travels over many LANs and WANs. These networks are frequently consisting of a variety of network equipment which would be based on many different versions of ethernet standard. Some devices would be running on 100-Mbps Fast Ethernet. Some would be running on Gigabit Ethernet 1-GE, 10-GE etc. The consistent format of frames provides the consistent format of your data and allows you to have a complete BACKWARD compatibility.
These frames travel over your ethernet networks to move your data between computers situated in your network. These frames are part of your 'Data-Link' layer (Layer 2) of OSI Model. That's why, your ethernet switches are called Layer 2 switches.

All ethernet switches are based on the functionality of 'Transparent Bridging,' and it is very crucial for the working of your switches. It means that your switch automatically begins working without you requiring any configuration on a switch or changes to your computers in the network (i.e., the operation of the switch is transparent).

What makes it possible for a network admin to add new connected endpoints to the network, without them having to manually configure the switch or the end-points?
It becomes possible because your switches are capable of learning about your MAC addresses. You would know that each port on your switch has a unique MAC address.

As frames are received on these ports, the software in your switch looks at the source address and stores this address to a table of MAC addresses. It constantly keep updating and maintaining the table which is also known as a 'Forwarding' database.

This is how, your switch DISCOVERS what devices are reachable on which ports. This forwarding table/database is then used by your switch to make decisions about HOW to filter traffic to reach certain destination address(es). Remember, these decisions are made on the basis of MAC addresses of the devices. IP addresses are nowhere in this picture. That is the main reason that your ethernet switch can learn which devices are on which segments of the network using the source addresses of the frames it receives.

Next part of the operations of your switch(es) is relatively easy. Your switch only needs to identify the port that is associated with the destination MAC address of the frames it receives. This ensures that traffic does not unnecessarily flow the other ports of the switch.

Your switch does not forward all frames onto all its ports - if it did this then your network would soon become overloaded. Instead the switch forwards the relevant frames to the relevant ports, as mentioned above. Also that the frames received are forwarded on WITHOUT any change, making the switch totally transparent to the systems on the local area network, or WAN network or whatever form of network it is.
As will sometimes happen, the Ethernet switch will receive a frame that is destined for a station or device that is new. When this happens the switch sends out a frame to all the ports, other than the one on which it received the frame with the unknown destination to discover the station which has the required address.
On a side note, your ethernet switches are capable of sending frames to multicast (and broadcast) MAC addresses too....These addresses are used for dynamic address- assignment, or sending data in multimedia applications to multiple users on a network at once.

Managed vs. Unmanaged
Unmanaged Ethernet switching refers to switches that require no configuration from you as an user. You can simply plug them in and turn on, and they are ready to work.
Unmanaged switches are typically for basic connectivity and they are often used in home or small office networks or wherever a few more Ethernet ports are needed, at a desk, in a lab, in a conference room, etc.
Managed Ethernet switching refers to switches that you can manage and program to deliver certain outcomes and perform certain tasks, from adjusting speeds and combining users into subgroups, to monitoring network traffic, etc.

Managed switches give you greater security with more features and flexibility because they can be configured to custom-fit your network. With this greater control, it is possible to better protect your network and improve the quality of service for those who access the network. The traffic can be prioritized so that the available bandwidth, etc is allocated to a given application, etc in the best way.

There are, however, also another type of switches referred to as an industrial switches.
They are typically used for industrial control, and similar applications. They are called industrial switches because they are used within industrial environments requiring a high level of robustness and tolerance of wide temperature ranges, etc. In addition to this, industrial switches feature 'carrier grade' ethernet performance, because industrial and production environments need to have very high reliability in view of the costs of any disruption.

Layer 3 Switching
Basically these are hybrid devices which combines the packet handling of routers and the speed of switching. These multilayer switches operate on both Layer 2 and Layer 3 of the OSI network model. The performance of this class of switches is aimed at the core of large enterprise networks.
Sometimes they are called 'Routing switches' or IP switches. These multilayer switches look for common traffic flows, and switch these flows on the hardware layer (Layer 2) for speed. For traffic outside the normal flows, the multilayer switch uses routing functions. This keeps the higher overhead routing functions only where it is needed, and strives for the best handling strategy for each network packet.
It is important to note that 'Multilayer Switching' is a generic term, encompassing any switch that can forward traffic at layers higher than Layer-2.

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