Internetworking in Computer Network

This tutorial explains basic internetworking concepts, such as collision domain and broadcast domain, with five key internetworking devices (hub, bridge, switch, router, and multilayer switch).

Internetworking is a term in computer networking that describes how computer networks connect using various networking devices. This tutorial explains basic internetworking concepts, such as collision domains and broadcast domains, using five key networking devices (hub, bridge, switch, router, and multilayer switch).

What is a computer network?

A computer network is a group of two or more devices connected for resource sharing. A resource can be anything. An essential computer network consists of three components: End Devices, Networking Devices, and Media.

End Devices: - End devices allow you to access or transmit the data. A computer, a laptop, a data server, and a tablet are examples of end devices.

Networking Devices: - Networking devices control the data flow. Switches, routers, hubs, bridges, firewalls, and modems are examples of networking devices.

Media: - Media transmits the data across the network. Copper cables, fiber cables, and wireless signals are examples of media.

The following figure shows a basic computer network.

Suppose you are on PC1 and want to send a file to PC3. For this, you can access PC3 from a network application, such as Network [Available in the left pane of Windows Explorer on any Windows OS], and drop the file into the shared folder on PC3. To send this file to PC3, PC1 follows these steps.

It starts the name resolution process. The name resolution process translates a hostname into an IP address and vice versa. It is the exact mechanisms that mobile phones use. When you dial a contact's number, what happens? Your mobile phone displays his name. This feature lets you see who is calling you or to whom you are calling.

For example, in the following figure, SAM (mobile number 098765432112) is calling BOB (mobile number 123456789012).

Neither Bob nor SAM has to remember each other's mobile numbers. Because the phonebook application saves mobile numbers along with their respective contact names. Phonebook is the smallest part of the DNS service. DNS service is the database of contact numbers and names.

Humans prefer names, while mobile networks use numbers. DNS maps both. It converts names to numbers and numbers to names during name resolution, as needed. The same thing happens in a computer network. You can replace the mobile network name and number with the computer network's hostname and IP address.

In a computer network, the source computer converts the destination hostname to the IP address. It uses DNS or ARP broadcasts to resolve hostnames to IP addresses.

In this example, PC1 is sending a file to PC3. PC3 is the destination address. PC1 must convert this address to an IP address before it can access it. PC1 uses the DNS service to resolve hostnames to IP addresses.

After learning the destination computer's IP address, the source computer needs one more address, called the MAC address. A MAC address is a hardware address and is burned into the Ethernet card by the manufacturer. It uses the ARP broadcast to find out the MAC address.

A sample broadcast from PC1 to find out the MAC address of PC3

Time    Source       Destination    Protocol  Info
8.123   192.168.1.1  Broadcast      ARP       Who has 192.168.1.3? Tell 192.168.1.1

A sample response from PC3 to PC1

Time    Source       Destination    Protocol  Info
8.124   192.168.1.3  192.168.1.1    ARP       192.168.1.3 is at 00:0b:db:99:d3:5e

Key Points

Every computer in a network has a unique network address. This address represents its location in the network. A computer address is composed of two parts: the IP address and the MAC address.

IP Address: - IP address is a software address. You must configure it on each PC.
MAC Address: A hardware address. It is assigned an Ethernet card from its manufacturer.

Computers know their own addresses. They do not know the addresses of other computers. To know others' addresses, they use two types of broadcast ARP and RARP.

Network applications rely on broadcast messages to get the necessary information. Besides ARP and RARP, other network broadcasts can cause serious performance issues. To address these issues, administrators divide an extensive network into multiple smaller networks. Each small network has its own broadcast boundaries and is known as a broadcast domain.

Broadcast domain

A domain is a group of computers sharing the same characteristics. A broadcast domain is a group of computers that listen to the same broadcast address. A broadcast message never carries user data. Computers use it for network functionality. Multilayer switches and routers can define boundaries for the broadcast domain.

Collision

Collision is another major network issue that every network faces. A collision occurs when two devices send data on the same media at the same time.

Collision domain

A collision domain is a group of computers that share the same collision domain. The more computers you put in a network, the more collisions you will experience. A collision seriously affects network performance. Collisions should be less than one percent of total traffic. If it increases, you will have to implement collision-removal devices. Bridges, switches, routers, and multilayer switches can control collisions.

Networking devices

This section describes five key networking devices used to connect multiple computers in a single network and explains how they affect broadcast and collision traffic.

Hub

If you have two devices, you can connect them directly with a cable. However, if you have more than two devices, you need a central device to connect them. A Hub is a central device. It connects multiple devices to a single network.

It is a multi-port repeater. It cannot control collisions and broadcasts. It is an outdated networking device. Modern networks no longer use it.

Bridge

A Bridge connects devices more intelligently. It can remove collisions from the network.

It keeps a record of connected devices and creates a separate route for each device. It has the following limitations.

• It cannot control the broadcast.
• It manages collisions through software that slows down overall network performance.
• It has limited ports.
• It is also outdated. Modern networks no longer use it.

Switch

Switches have all the goodies of bridges. They can control collisions at the hardware level, which improves overall network performance.

Switches create a separate route for each connected device, eliminating the need for CSMA/CD.

A switch keeps route information in memory. It maintains a table used to keep track of connected devices. It is known as the CAM table and is also used to remove collisions.

Switches can control collisions, but they cannot control broadcasts.

Router

A router can control both collisions and broadcasts.

Routers have the following drawbacks: -

• They are costly.
• They have limited ports.

Multilayer switches

Multilayer switches are the most expensive of these devices. They can control both collision and broadcast.

Typically, enterprise networks use multilayer switches.

Summary

Conclusion

This tutorial explained basic concepts and functions of a basic network. Later, it described how essential networking devices such as hubs, bridges, switches, and routers work in a network.