CCNA Study Guide

This tutorial explains basic concepts of network addressing including a brief overview of subnet, flat topology, IP address, Subnetting, Supernetting and VLSM.

Basic concept of Network addressing

Every computer in network has an IP address that define its location. Networks could have any number of computers. These computers are grouped in certain ways for easy finding. Courier companies follow same concept in delivering packets on correct address. For example you live in Singapore and have a parcel for your friend who live in Bhilwara. You write down the following address on parcel of your friend and give it to courier company.

Sanjay Kumar Goswami
D-131 Sundar Vihar Jothwara
Bhilwara Rajasthan
India

Now courier company would find this address in reverse mode. They will first send this parcel to their main office in India. In main office all parcels are filtered and grouped according to their destination state. This parcel would be grouped with other parcel headed to Rajasthan. Same process would be done at main office of Rajasthan. This time packages would filtered and grouped according to their district. Our parcel would be grouped with parcels headed to Bhilwara. At Bhilwara office our parcel would be handed over to the delivery boy. Delivery boy will go in Sundar vihar Jothwara. Their he will find the D sector. In D sector he will be locate the house number 131 and deliver the parcel. Neither you nor your friend would be aware about the process followed by courier company. You and your friend are only concerned about parcel that delivered successfully. Let take one more example you send one more parcel to the same friend, this time you only write down his name

Sanjay Kumar Goswami

What would happen this time? Will this packet deliver? Courier company needs address to deliver this package. So chance are, they would reject this package.

Accurate address is required to deliver the package. Same mechanism is used in computer network. In real life address is made from house number, street name, district name, state name and country name. In computer network address is made from host address, network address, subnet etc. Subnetting, Supernetting, VLSM are the terms those do filtering and grouping in computer network. In this article we will take a brief overview of these terms.

This tutorial is the first part of our article “Network Addressing Explained with Subnetting and VLSM”. You can read other parts of this article here.

Subnetting Tutorial - Subnetting Explained with Examples

This tutorial is second part of this article. In this part I will explain IP addressing and Subnetting in detail with examples. Later I will present an easy and unique method of Subnetting that will make it easier to understand.

VLSM Tutorial with Examples

This tutorial is the last part of this article. In this part I will explain VLSM in detail with examples. Later I will provide a unique six steps method of VLSM that will help you in learning VLSM rapidly.

IP Address

IP address is the address of device in network. Computer or network device understand only one language, binary language. In binary system all computers function using a system of switches that can be in one of two positions, on or off. Off being represented by the digit 0 and On being represented by the digit 1. A binary number will include only the digits 0 and 1. IP addresses are based on dotted decimal notation of a binary number. For example IP address 10.10.10.10 is a decimal notation of 00001010. 00001010. 00001010. 00001010

Network addressing

Companies often have large network, that need to be divide in smaller network for flexibility. These smaller network known as subnets and this process known as sunetting. Let's take an example of a company that have three story building, divided by floors, with each floor divided into offices. Think building as network, floors as subnets, and office as host.

Example of subnets

Subnet

Subnet is a group of computers divided by layer 3 IP address. Subnet have hierarchical structure. Some bits from host portion are taken to create subnet address. Our next article describe this process in detail.

Flat topology

Without subnet network has flat topology that relies on layer 2 MAC address to deliver packets. MAC address has no hierarchical structure. All devices share same layer 2 broadcast domain and bandwidth. As network grows, use of bandwidth become less efficient.

Subnetting

Subnetting is a process of breaking large network in smaller network known as subnet. Subnet are easier to manage. Subnetting reduces network traffic, which improve network performance. In subnetting some bits of host address are used in subnet address.

Supernetting

Supernetting is a reverse process of subnetting. Supernetting is done at router, for route broadcast. Supernetting allows router to keep its routing table as small as possible. Router relies on routing to determine route for packet. Router broadcast its routing table so other router can learn about the network it have. As network grow routers require huge memory tables to store all routing information. Supernetting helps reduce the size of router memory tables by combining and summarizing multiple routing information entries into one single entry.

Differences between Subnetting and Supernetting

  • Subnetting breaks large network in smaller networks, while supernetting combine smaller networks in single possible large network.
  • Subnetting is done to reduce the network traffic, while supernetting is done to reduce the size of routing table.
  • Subnetting reduce collision and broadcast traffic between subnets. Supernetting reduce broadcast traffic between routers.

VLSM

In subnetting all subnets have same number of hosts as they use same subnet mask. This leads to inefficiencies. For example, if you borrow 4 bits on a Class C network, you end up with 14 valid subnets of 14 valid hosts. A serial link to another router only needs 2 hosts, but with classical subnetting, you end up wasting 12 of those hosts.

With VLSM, you can summarize subnets back to the Class A, B, or C network boundary. For example, if you have a Class C network 192.168.1.0/24 and subnet it with a 26-bit mask, you have created four subnets. Using VLSM and summarization, you can summarize these four subnets back to 192.168.1.0/24.

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