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CIS 115

How the Internet Works

Circuit Switching

Image Source: Wikipedia

Packet Switching - Paul Baran

Image Source: Wikipedia

7 Layer OSI Network Model


Image Source: Wikipedia

Physical - 100BASE-T

Image Source: Wikipedia

Data Link - Ethernet

Image Source: Wikipedia

Network - IPv4

IPv4 Packet Structure
Version InfoLength
Packet IDFlags & Offset
Protocol & TTLChecksum
Source IP Address
Destination IP Address

IPv4 vs. IPv6

IPv4: 32 bit Addresses
232 = 4,294,967,296

IPv6: 128 bit Addresses
2128 = 340,282,366,920,938,463,463,
or 340 Undecillion addresses

Network - IPv6

Image Source: Wikipedia

Image Source: XKCD

Transport - TCP

TCP Packet Structure
Source PortDest. Port
Sequence Number
Acknowledgement Number

Transport - UDP

UDP Packet Structure
Source PortDest. Port


Connection OrientedConnectionless
AcknowledgeNo Acknowledge


Domain Name System (DNS)
"Phonebook for the Internet"

Image Source: Wikipedia

DNS Lookup

Image Source: Wikipedia

Dynamic Host Configuration Protocol (DHCP)

Image Source: Tech Juice

HyperText Transfer Protocol (HTTP)

Image Source: Wikipedia

Image Source: Wikipedia

HTTP Commands

HTTP Status Codes

HTTP Status Codes


Blog 4: The Internet's Influence

The internet has been a major force in our lives for several decades now. Write about how the internet has influenced you as a person. Try and think about ways that you would be a different person if you didn’t have the internet. Things you can think about:The internet is a very influential part of our modern culture. Because of this, most of us have been impacted by the internet in some way throughout our lives. For this blog article, write about how the internet has impacted you as an individual, but also how you believe the internet has impacted us as a society in general. (Food for thought: - read about the Filter Bubble or Cyberculture for ideas: and As you are writing, here are some things you can think about:

DHCP Request

DHCP Response

DNS Lookup

DNS Response

HTTP Request

HTTP Response