The knowledge about Local Area Networks or LANs is essential for a person to pass CCNA 100-101 ICND1 exam as it is one of the major sections in the course outline.

What is a LAN?

LAN stands for Local Area Network. It is a small network limited to a small office or building.

Components of a LAN:

A LAN network should have some basic components like computers, servers, switches, routers etc. Suppose we have two computers and we want to communicate information between them, for this we should have some way of interconnecting these computers. For this purpose we can use devices like NIC (Network Interface Card) and media which include the physical medium like fiber or copper cable. Other interconnecting devices include routers and switches.  Router is used to connect one network to another while switches allow us to connect multiple devices within a network with each other.


In the figure above, Computer A and Computer B communicate with each other logically but a fact is that there is a physical switch between these computers which allow this communication. All this communication is transparent between these devices via this switch.

Network Protocols:
Network Protocols can be referred to the set of rules that are followed while transferring data from one device to another in a network. In the network there are different areas where different protocols or rules are followed for communication.

Network Protocols

In the above we have a LAN network having host / computer, a server, a switch and a router. This LAN is connected to the WAN or internet via router. Different protocols will be followed in communication between different devices in the above pictorial illustration.

The communication between Host and the Server will follow the IP protocol for logical addressing and Ethernet protocol for physical addressing. Here the concept of Address Resolution Protocol or ARP is applied, ARP is used to lookup Ethernet connection based on IP address. ARP is very important in a network to find out what actually happening in a network and ARP defines the behavior how devices will communicate is a network.

The need of switches:
The switches are very critical in a network as they connect all the devices in a network together for the communication. Switches act as a central point in a network, the best example for that is Start topology in which all the devices are connected to a single switch and all the communication takes place via that central point or a switch.

  • Types of Switches:
    The switches are available with different number of ports on them. A switch can have 8, 12, 16, 24, 48 or 96 ports in it. So we have a possibility to connect a large number of devices to a single switch.

Issues in a LAN:
Collision of signals / information packets when two devices try to communicate simultaneously is the basic issue that most of the LANs face.

Following is the solution for above problem:

  • CSMA/CD:
    It stands Carrier Sense Multiple Access with Collision Detection, it is a tool that is use to prevent the devices from trying to communicate simultaneously across an Ethernet wire. It will send instructions to the different hosts that are going to transmit the information in a network to wait so that the collision can be prevented.
  • Routing and Switching:
    In the large networks, the possibility of collision is greater and to prevent that we have to use the concept of routing and switching.

The routers basically break the Broadcast Domains and the switches break the Collision Domains to prevent the collision between the traffic on a network.


In the above figure, we have a switch and three hosts connected to switch. Suppose Host C is trying to communicate and sends a message to a switch while on the same time Host A also sends a message to the switch, in this case the switch will give instruction to one of these hosts to wait until the former message is being transferred.

Carrier Sense Multiple Access with Collision Detection or CSMA/CD is an out dated technology for the prevention of collision while routing and switching the latest and up to date method being used for this purpose.

Functions of a Switch:
Switches have four basic functions which are going to be discussed below:

  1. The switches basically operate at the link layer to support TCP/IP suite. The switch is going to provide services to the next layer in the TCP/IP or OSI model.
  2. Another important job performed by the switch is to Forward, Filter or Flood the frames and all this is done on the basis of MAC address. Switches have some tables which store the MAC addresses of the devices in a network.  Suppose the switch receive a request to communicate with a device whose MAC address isn’t found in the table, the switch will flood that message to all the devices in the network and in case of not finding the desired MAC address the message will be filtered. While if the device with desired MAC address is found in a network, the message will be forwarded to that specific device.
  3. The switches also create separate collision domains. Suppose if a switch have 196 ports, it means it has 196 collision domains but there is no possibility of the collision in this scenario. The switches also give us the capability for full duplex speed. Full duplex communication means to way communication i.e a device can send and receive the messages simultaneously.
  4. The switches also support the variable speeds. It means that the switch can support the network cards with different memories i.e 10 mbs, 100mbs or 1 GB. It is one of the primary benefits provided by the switch.

The above four points are critical for setting up a large network. Without switches we cannot set up a network. Without switches we cannot connect multiple devices and support network devices with variable speeds.

For the network professionals, the understanding of LANs in different aspects is essential. The above discussion is helpful to understand the operation of LANs, their components and functions of those components.

Learn More:
Visit the link below to get benefit from our Lesson 5 which focuses on Ethernet and Switch Operations

Preparation of CCNA 100-101 Exam:
After getting all the technical knowledge about 100-101 exam, the candidate have to prepare for passing this exam. The practice tests are a best tool / way to prepare for the real 100-101 exam as it is a simulator of a real exam.