Presented by Rebecca Meinhold

But How Does the Internet Work?

Let’s get started with the basics

First thing you need to know is that every

computer has an IP address

There are TWO ways in which a computer gets an IP address:

Static Method Dynamic Method

A computer administrator will manually set the IP address to the

machine

The Dynamic Host Control Protocol (DHCP) server is responsible for assigning IP

addresses to all computers on the network

IP Addressing

Different Types of IP Addresses

There are two different types of IP

addresses

Private

Personal computers are usually assigned private

IP, which is then connected to a router

with a public IP

Public

Servers typically use public IP addresses

Searching google.com

Your computer Your router/ domain name server

Google’s IP address

• A request is sent to the router to find out the IP address of the domain name

• Here is where the domain name is converted into it’s IP address

• Once the IP is known, the DNS server sends an HTTP GET request to Google’s particular IP

google.com

74.125.224.72

HTTP GET request

MAC addresses are added in the data link

layer before the packet heads to the

physical layer

In the network later, information related to

source & destination IP addresses are are

added and then are sent to the Data Link layer

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

HTTP GET request

Packet

Packet

Packet

Requests are encapsulated in the

form of transport layer packets and

then are sent to the network layer

Post DNS Stage

Two protocols operate in the Transport Layer:

UDPTCPUser Datagram ProtocolTransmission Control Protocol

Ensures that the packet is not larger than the largest protocol data

unit in the path located between your computer

and the destination

Offers a limited amount of service

when messages are exchanged between

computers in a network that uses IP

The router searches it’s cache for the

packets host address, when found, it

forwards the packet to it’s destination

Packet

Your computer Router Destination

Packet

When the packet leaves your computer, the MAC Address of the router in

which your packet is being transferred to is used as the packets destination

MAC Address

The following slide will show the process that the packet goes through while traveling to it’s destination

HTTP GET Request is passed to the application listening on the

port

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical LayerPacket

Packet

Packet

Packet

IP address checks and check-sum

verifications are done before passing to the

transport layer

The MAC address is checked to see if the

packet is at the correct destination

The response is then formed and transmitted back in the same way

that it came in