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CCNA R&S Article #6 – Understanding Ethernet Local Area Network


CCNA R&S Article #6 – Understanding Ethernet Local Area Network

Today let’s talk about Ethernet LANs. Before we start, let’s understand the Ethernet. Ethernet is a set of standards that defines the physical and the data-link layers of LAN. These standards are defined by the IEEE (Institute of Electrical and Electronics Engineers) – the standard documents the cabling, connectors, and protocols specifications required to build a LAN. Anyone who is interested in standards defined by IEEE for Ethernet Click here.

Now that you got an idea of what is Ethernet, let’s discuss the types of LANs. LAN is the correct implementation of Ethernet standards in the real world.

Small Office Home Office

As the name indicates this type of network implementation is small in scale providing connectivity to the devices at home or in a small office. At the minimum, this network needs a device called LAN Switch. LAN switch is an aggregation device, where all devices like computers, printers, etc. are connected. These devices are connected through Ethernet Cables.

Figure 1: SOHO LAN

You can see there are three Personal Computers, one Printer, and one router connected to the aggregating device which is a LAN switch or Hub. If you have noticed, there is another type of device connected to the LAN Switch, it is a router. A router in any network generally connects a LAN to the external network (Internet) to access services that exist outside in external network. In a SOHO network, these two devices (LAN Switch and Router) are combined into one device.

Wait a minute my home network doesn’t look like one as I don’t have any cable connected to my PC or printer. Yes typical SOHO LANs today also support wireless connections to allow mobility where you can use any area in your home to perform your work and you don’t need a cable to connect to the network. 

IEEE defines this type of connectivity as Wireless LAN and is documented in IEEE 802.11 standards. Wireless LAN specifications standards start with 802.11 numberings and are NOT Ethernet.

Figure 2, shows the same SOHO network as above but added with Wireless LAN connectivity. In a Wireless LAN network, you need a special device called Access Point (AP). The AP role is to connect wireless devices (Laptops 1 and 2) to the wired device Ethernet Switch. This arrangement allows the Laptops to access a printer that doesn’t support wireless connectivity.

Figure 2: Wireless LAN w/ Laptops

Again, all three functions (Switch, Router, and Access Points) are combined into one device at your home network. Now that you got an idea of SOHO LAN and its basic components, let’s expand the scope and move to an Enterprise LAN.

Enterprise LAN

Enterprise LAN is not different from the requirements of SOHO LAN but one thing that differentiates it from SOHO is its scale. The enterprise network covers large areas where users or devices are located. Try to imagine an enterprise network where users are grouped into departments like Sales, Marketing, Engineering, HR, Finance, etc. These departments are in a building on multiple floors.

When you try to implement an Enterprise LAN with the above scale, the SOHO network cannot scale well and you may end up with multiple SOHO networks to meet this requirement. Now you need different layouts and cabling plans for your network. There will be multiple types of switches to provide connectivity –

  • Access Switch – where all users will be connecting
  • Distribution/Core Switch – where all access switches will be connected
  • Access Points – to connect wireless devices
  • Wireless Controllers – to manage multiple Access Points from one locations
  • Routers – to connect Enterprise LAN to the Internet or to a second branch located in a different city or country.

Let’s try to design a high-level architecture of an Enterprise network with the required components.

Figure 3: Enterprise LAN Design

As per the above Enterprise LAN Diagram, you can clearly see we are not dealing with few hosts and one LAN switch. In this Enterprise LAN, there are hundreds of users connected to the network using wired and wireless connectivity. Access switches are connected to Core Switch. Router not only provides Internet connectivity to this enterprise but also this site can talk to other sites located in different locations.

I don’t want to stretch this more, let’s talk about Ethernet standards that define what is the type of cables these networks are using, the type of connectors, how they uniquely identify hosts, etc. in separate articles.

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