Introduction to Internetworking In Computer Networks

To Start with Let define what Internetwork is: You Set up an internetwork when you connect two or more networks via a Layer3 device such as a router and assigned a logical network addressing such as IPv4 or IPv6. The Word internetworking comprises of two major words inter which means between and networking which means concatenating or joining networks together. Internet is the most common example of Internetworking, which means a network of networks.

We have 3 types of internetworking which are stated below:

  1. Intranet
  2. Extranet
  3. Internet


The word Intranet should not be confused with the Internet, Intranet is a private network owned by an organization for sharing information and collaborations excluding access from users outside the company network.

Benefit of Intranet

1.Effective communication: Intranets permit fast communication within an organization. It enables employees within the organizations to communicate effectively keeping everyone fully engaged and informed.

2. Collaboration: Intranet provides effective collaborations with each staff in a different department within the organization. This collaboration allows employees from different departments to work together to achieve a common objective.

3. Increase Company Productivity: Intranet Increases productivity by allowing users to perform their jobs faster and accurately because it enables users to locate and view information faster. It breaks the barriers of users spending more time to find a required document which may affect the company productivity negatively.

4. Web Publishing: Web publishing is the process of publishing original content on the internet. Web publishing use web technologies to access document, training, company policies, new feeds and can be access over web browsers.

5. Cost: The amount of money invested in setting up an Intranet is extremely small.

6. It Enhance Common Corporate Culture: Intranet allows every employee within an organization can view and work with the same information.


An extranet is private network organizations use to allows trusted third parties such as customers, vendors, partners, and suppliers to have secure access to business information. An extranet is more like a DMZ it provides access to authorized third parties, without granting access to organizations’ entire networks.

Benefit of Extranet

  1. Improve efficiency: Organization of all forms often work with multiple partners and external vendors to develop product and complete tasks. When customers are satisfied with the information provided it’s an advantage to the organization because they will get more customers which will increase efficiency.
  2. Effective Collaboration and Knowledge with other companies on joint development efforts.
  3. Effective communication and engagement for employees and partners.


The Internet is a network of networks that consist of private, public, business, and government networks of local to globally linked by electronic, wireless, and optical network technologies.

Benefit of Internet

  1. Work from home, collaboration, and access to a global workforce: An Internet connection gives many people an option to create a virtual office by allowing them to work from home, this happens during the Covid-19 pandemic which prevents a lot of employees from having access to their working place. In this condition, the Internet plays the most important role as it provides connectivity between all employees, through which they all can communicate and discuss with each other any project.
  2. Internet of Things: The Internet makes smarter your device in your home and giving them access to the Internet.
  3. Entertainment: The Internet provides people to access endless entertainment. With the Internet, you can watch movies, videos, play games online, listen to music, etc.
  4. Banking, bills, and shopping: Another advantage of the Internet is online shopping, which allows people to find products of interest and buy them without having to visit a store. You can compare prices between companies for any product through the Internet
  5. Information, knowledge, and learning: The Internet allows people to learn information about any topic and offers an answer to any type of question, as it contains endless knowledge and information.

Internetworking Models

When networks first came into being, computers could typically communicate only with computers from the same manufacturer. For Instance, companies ran either a complete OEM solution such as IBM or Dell, never both together. A model was created by International Organization of Standardizations(ISO) know as Open system Interconnection (OSI) was create to break the barriers of not allowing different OEM solutions to communicate.

The OSI model is the fundamental architectural model for networks, which describe how data and information are communicated from one computer application to another via a network media. The OSI model have 7 layers which are divided into two groups. The top three layer define how applications within the end device communicate with each other as well as end users. The bottom four layers defines how data is transmitted end to end.

The OSI reference model has the following seven layers:

1. Application layer (layer 7)

2. Presentation layer (layer 6)

3. Session layer (layer 5)

4. Transport layer (layer 4)

5. Network layer (layer 3)

6. Data Link layer (layer 2)

7. Physical layer (layer 1)

Some people like to use a mnemonic to remember the seven layers, such as

All : All stands for Application.

People : People stands for Presentation.

Should : Should stands for Session.

Try : Try stands for Transport.

New: New stands for Network.

Data : Data stands for Datalink.

Plan: Plan stands for Physical.

Let explore each layer of the OSI model.


The Application layer is working as the interface between the actual application program

and the next layer down by providing ways for the application to send information down

through the protocol stack.

The Presentation Layer

The Presentation layer presents data to the Application layer and is responsible for data translation and code formatting. One very effective way of ensuring a successful data transfer is to convert the data into a standard format before transmission. More also some key functions of the presentation layer include data compression, decompression, encryption, and decryption.

The Session Layer

The Session layer is responsible for setting up, managing, and dismantling sessions between Presentation layer entities and keeping user data separate.

The Transport Layer

This layer provides end-to-end data transport services and can establish a logical connection between the sending host and destination host on an internetwork. This layer has two well-known protocols which are TCP and UDP. The TCP is connection-oriented while the UDP is not.

The Network Layer

The network layer belongs to layer 3 of the OSI model, this layer manages device addressing, tracks the location of devices on the network, and determines the right path to move data. The layer transport traffic or data between devices that are not in the same jurisdictions. The router is a layer 3 deices which provide routing services with internetwork.

This is how a router works when a packet is received on a router interface, the router checked the destination IP address of the packet and if the packet is not destined for that particular router the router will look for the destination network address in the routing table. Once the router chooses and exits the interface, the packet will be sent to the interface to be framed and sent out on the local network. If the router can’t find an entry for the packet destination network in the routing table, the router drops the packet.

We have two types of a packet used in the network layer which are stated below;

1. Route Update: The Route Update is used to build and maintain a routing table. This packet helps to update neighboring routers about the networks connected to all routers within the internetwork. The protocols used to send route update packets are known as routing protocols which are RIP,RIPv2, EIGRP and OSPF.

2. Data Packet: The data packet is used to transport user data or information through internetwork. The protocol that supports the data traffic is known as routed protocols which are IP and IPv6.

Take note: Each Interface on the router is a separate network, below are some router characteristics you should never forget.

a. Routers, by default, will not forward any broadcast or multicast packets.

b. Routers use the logical address in a Network layer header to determine the next-hop router to forward the packet to.

c. Routers can use access lists, created by an administrator, to control security based on the types of packets allowed to enter or exit an interface.

d. Routers can provide layer 2 bridging functions if needed and can simultaneously route through the same interface.

e. Layer 3 devices—in this case, routers—provide connections between virtual LANs (VLANs).

f. Routers can provide quality of service (QoS) for specific types of network traffic.

The Data Link Layer

The Data Link layer will ensure that messages are delivered to the proper device on a LAN using hardware addresses and will translate messages from the Network layer into bits for the Physical layer to transmit. This layer handles the physical transmission of data and handles error notification and network topology.

For a host to send packets to individual hosts on a local network as well as transmit packets between routers, the Data Link layer uses hardware addressing.

The data links have two sublayers which are stated below:

1.Media Access Control(MAC): This defines how the packet was placed on the media.

2. Logical Link Control(LLC): Responsible for identifying Network layer protocols and then encapsulating them.

The switch and bridge belong to the data link layer and filter network using hardware addresses know as MAC addresses.

NOTE:  Data is encoded with control information at each layer of the OSI model, the data is named with something called a Protocol Data Unit (PDU). At the Transport layer, the PDU is called a Segment, the Network layer is Packet, Data Link is Frame, and Physical layer is Bits.

Let have a brief discussion on the switch: A switch is a Layer 2 device that is considered a hardware-based bridging because it uses specialized hardware known as application specific integrated circuit (ASIC) which runs on high gigabit speed with low latency. Latency is the time measure from when a frame enters a port to when it exits the port.

The biggest benefit of using switches instead of hubs in your internetwork is that each switch port is actually its own collision domain.

The Physical Layer

The Physical layer does two things: it sends bits and receives bits. Bits come only in values of 1 or 0.

This layer is also where you identify the interface between the data terminal equipment (DTE) and the data communication equipment (DCE). (Some old phone company employees still call DCE “data circuit-terminating equipment.”) The DCE is usually located at the service provider, while the DTE is the attached device. The services

available to the DTE are most often accessed via a modem or channel service unit/data service unit (CSU/DSU). The hub operates at the physical layer of the OSI model.

A hub is really a multiple-port repeater. A repeater receives a digital signal, amplifies or regenerates that signal, then forwards the signal out the other port without looking at any data. A hub does the same thing across all active ports: any digital signal received from a segment on a hub port is regenerated or reamplified and transmitted out all other ports on the hub. This means all devices plugged into a hub are in the same collision domain as well as in the same broadcast domain.

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