Internet

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Rounters

  • Try tracert -d www.google.com in Command Prompt (Windows),
    traceroute -n www.google.com in Terminal (macOS/Linux)
  • Try again without -d (or -n)
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Protocols

  • TCP/IP
  • UDP
  • DNS
  • DHCP
  • HTTP/HTTPS, SMTP/POP3/IMAP, FTP/SFTP, SSH, WebSocket, ...
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TCP/IP

  • IP
    • #.#.#.# (IPv4)
    • #:#:#:#:#:#:#:# (IPv6)
  • TCP
  • Port
    • 80: HTTP
    • 443: HTTPS
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Feature TCP UDP
Reliability Reliable Not reliable
Data Integrity Ensures data integrity No data integrity guarantee
Sequencing Ensures data sequencing No data sequencing
Connection Connection-oriented Connectionless
Speed Slower due to reliability Faster due to lack of reliability
Flow Control Provides flow control No flow control
Usage Web browsing, email, file transfer Streaming, real-time applications
OSI Layer Transport Layer (Layer 4) Transport Layer (Layer 4)
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DNS

  • Try nslookup www.babson.edu
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Domain Name IP Addresss
localhost 127.0.0.1
google.com 142.251.35.174
github.com 140.82.114.4
one.one.one.one 1.1.1.1
babson.edu 155.48.7.191
www.babson.edu 34.226.183.173
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DHCP

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HTTP

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HTTPS

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https://www.example.com

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https://www.example.com/

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https://www.example.com/path

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https://www.example.com/file.html

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https://www.example.com/folder/

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https://www.example.com/folder/file.html

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https://www.example.com/folder/file.html

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https://www.example.com/folder/file.html

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https://www.example.com/folder/file.html

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https://www.example.com/folder/file.html

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https://www.example.com/folder/file.html

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HTTP Requests


GET

POST

...
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HTTP Request Header


GET / HTTP/1.1
Host: www.example.com
...
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HTTP Request Header

Examples:

GET / HTTP/1.1
Host: www.babson.edu
...


GET /search?q=cats HTTP/1.1
Host: www.google.com
...
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HTTP Response Header


HTTP/1.1 200 OK
Content-Type: text/html
...
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Example (HTTP via curl)

  • Request
    curl -I http://www.babson.edu
...
  • Response
    HTTP/1.1 301 Moved Permanently
Location: https://www.babson.edu/
...
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Another Example (HTTPs via curl)

  • Request
    curl -I https://www.babson.edu/something-funny
...
  • Response
    HTTP/1.1 404 Not Found
...
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200 OK
301 Moved Permanently
302 Found (or Moved Temporarily)
304 Not Modified
307 Temporary Redirect
401 Unauthorized
403 Forbidden
404 Not Found
418 I'm a Teapot
500 Internal Server Error
503 Service Unavailable
...

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418 - I’m a teapot

  • Request
    curl -I -X GET https://www.google.com/teapot
...
  • Response
    HTTP/1.1 418 I'm a Teapot
...
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Another 302/301 Example

GET / HTTP/1.1
Host: BabsonRejects.com
...

GET / HTTP/1.1
Host: BentleyRejects.com
...
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Activity: pass a mail/envolop to a student

sheme, or protocol

Use Chrome Incognito mode and Dev Tool on www.babson.edu and www.babson.edu/index.php

https://twitter.com/alexxubyte/status/1708863540067696878