The knowledge about Ethernet and Switch operations is essential for a person to pass CCNA Routing and Switching 100-101 exam as it is one of the major sections in the course outline.

Introduction of Ethernet:

Ethernet LAN Connection Media:
The Ethernet cable used in the network can be one of the following types:

  • Coaxial Cable (not used anymore)
  • Copper
  • Fiber-optic

When we have to connect different devices in a network, we have a variety of options available for that. We can use copper cable or fiber optic cable. The selection of medium depends upon different factors i.e. distance and cost. The fiber optic cable can carry information to a large distance as compared to copper cable. As far as cost is concerned, the optic fiber is much expensive as compared to copper cable. So while setting up a network cost and distance should be kept in mind. Most of the Cisco devices support fiber optic cables.

Copper Wire as UTP Cable:cable-utp-bobina-305-mts-cca-cat5e-exterior-calibre-24awg

UTP cable stands for Unshielded Twisted-Pair cable. Inside the outer jacket of UTP cable, there are 8 wires which are grouped in the form of pairs i.e. 4 pairs. The two wires in a pair are twisted with each other. The wires are twisted in way that in each inch there are almost 22 rotations. This twisting of wires in UTP cable can reduce the effect of Radio Frequency Interference or RFI. RFI is the disturbance that affects an electrical circuit because of the electromagnetic induction or radiation emitted from the external source. Moreover it also reduces the impact of Crosstalk. Crosstalk is the scenario in which the message flowing in one pair of wires overlaps or mixes with the message flowing in the other pair. The twisting of wires also helps to reduce this effect. The UTP cables are connected to the devices in a network through RJ-45 connector.

Characteristics of UTP Cable:
Speed: The speed of data transmission in UTP cable varies from 10 MB / second to 10 GB / second. It is indirectly proportional to the distance i.e. shorter the distance, greater the throughput or transmission speed and vice versa.

  • Cost: The average cost of UTP cable per node is much lesser than other media.
  • Cable Length: The maximum cable length for UTP varies depending upon the current scenario or network.
  • Media or Connector Size: It is smaller because of the use of RJ-45 connector.

Wiring Standards:
The wiring standards mostly used in UTP are 568A and 568B. These standards govern the rules that which pair should be terminated where in the RJ-45 connector. We can made different types of cables such as Straight-through Cable or a Crossover Cable.

Straight-through Cable: The straight-through cable is used to connect computers to switches or the routers to switches.
Crossover Cable: This cable is used to connect to similar devices such as two computers or two switches.

Fiber Optic Cable:

In the Fiber Optic cables, the transmission of data from one point in a network to another point takes place in the form of light signals. It a faster way to transmit information and is used for transmission across long distances. The inner core of a cableismade up of glass so that the light signals can be reflected from its walls and move forward in a zigzag manner. The outer cladding or insulator is made up of fiber to prevent the emission of light.

Types of Fiber Optic Cables

  • Multi-mode Fiber: It is used to transfer a lot of individual signals and maintain the integrity of those signals over the moderate distances. The multi-mode fiber has fiber optic conductor of 50um width. The width of insulator which is referred as cladding is much smaller than cladding of single-mode fiber.
  • Single-mode Fiber: It can carry a single signal at one time to transmit it from one machine to another machine so there is no need to worry about integrity of signals. This type of optic fiber cable is best in case we have to transmit signal to a large distance. The single-mode fiber has fiber optic conductor of 9um width. The width of insulator which is referred as cladding is much larger than cladding of multiple-mode fiber.

Types of Communication:com

  • Unicast: The unicast communication refers to one-to-one communication which means that one computer in a network want to communicate with another one computer.
  • Broadcast: The broadcast communication refers to one-to-all communication which means that a device in a network sends information which is to be sent on every other device in that network.
  • Multicast: In this type of communication, a computer sends a message for a group of devices with specific group addresses. Multicast is also used in the military for the purpose of communication. Multicast is better than broadcast in a sense that it utilize less bandwidth as compared to broadcast.

Switching Operations:

MAC Table: The MAC table in the switch contains the MAC addresses of all the devices connected to it in order to find the specific device.

MAC Table Working:


In the above figure, there are three computers which are connected to a single to form a network. Suppose Computer A wants to send a frame / data packet to Computer C. For this purpose, the sender will send this frame to the switch which is acting as a hub in the network. Now the switch is familiar with the device from which frame is coming so it will update its MAC address table and adds the MAC address of Computer A / sender in it. The problem is, this table do not have any information about the Computer C / receiver, at this point the switch have to follow some rules to find out the receiver device. So the switch will implement the rule of flooding, which means that this frame will be sent to all the devices in a network except Computer A / sender. When the frame will reach on the Computer B (it is not a receiver), it will respond that its MAC address is not that for which the switch is searching, so the frame will be dumped in the garbage. But when the frame will reach at the Computer C which is actually a receiver device, it will response in a positive manner and will accept the frame as the MAC address in the frame matches with the address of Computer C. Now the switch will update its MAC address table again by adding the address of Computer C in it. The switch will respond back to the Computer A to notify that the specific receiver has been found.

From the above discussion we come to know that the Ethernet connection can be developed using different types of media such as Fiber Optic Cable or Copper wire. Speed of data transmission is much faster in optical fiber as compared to copper wire but it is expensive as well.

Switches perform a number of tasks in a network to make sure that the communication can be done smoothly. A Switch have a typical table named as MAC address table which stores the MAC address of all the devices connected to it so that it can help those devices to communicate with each other.

Learn More:
Visit the link below to get benefit from our Lesson 6 which focuses on IP Addressing and Subnetting

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

Finding these practice exams is not an issue now as Selftest Training, a leading name in the certifications industry, provides these practice tests to ensure that the candidate should pass the 100-101 exam in first attempt.