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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 Filter Bubble

The Filter Bubble ( is a phenomenon on the internet where personalized algorithms present users only with information or opinions that match her or his own thoughts. Because of this, internet users can become isolated in their own little worlds, where everything they see and hear agrees with an reinforces their own ideals and belief. For this blog post, we want you to challenge yourself a bit to see exactly what others are seeing. Here's what we'd like you to do:

  1. Find someone (a friend, family member, roommate, fellow student, etc.) who has different thoughts and opinions than your own. It doesn't have to be purely politically based; they may like different games, movies, websites, books as well.
  2. Using their personal computer (with their permission and while they are present), browse the web for a little bit. Do a few searches on Google or Amazon, check out the recommended videos on Youtube or Netflix, see what ads are appearing on different sites, etc. If you do this on a shared computer or lab computer, have them log in to a few sites and search around for a bit like they normally would before handing it over to you.
  3. Then, do the same steps on your own machine or while logged in to your own accounts, and record the differences.
  4. Bonus - Use private browsing or incognito mode and repeat those steps again. Is it different?

Write about your experiences and what you find. Make sure you reference back to the textbooks and other websites to help you explain why this is happening.

DHCP Request

DHCP Response

DNS Lookup

DNS Response

HTTP Request

HTTP Response