The BEST OSI Model Explanation You'll Ever Watch (Networking Fundamentals) — Transcript

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1. 0:00The OSI models have been explained many,
2. 0:02many, many times in the past, but maybe
3. 0:04not with this level of clarity. The OSI
4. 0:06model is a networking model, and it has
5. 0:07seven layers, and we're going to trace
6. 0:09how an HTTP request travels through each
7. 0:12one. Think of it like a letter getting
8. 0:14wrapped in envelopes, each with
9. 0:15different information from your browser
10. 0:17to a web server and back. Let's see what
11. 0:18happens at each layer. Let's start with
12. 0:20our example. You're browsing example.com
13. 0:23at layer 7. And your browser is going to
14. 0:25create an HTTP request called get
15. 0:26index.html.
16. 0:28This is the actual data you want to
17. 0:30send, pure application stuff. It's like
18. 0:32writing a letter saying, "Please send me
19. 0:33the homepage." Now, layer six steps in.
20. 0:37This layer is responsible for things
21. 0:38like formatting, compression, and
22. 0:39character encoding. And it's like
23. 0:40putting your letter inside of a lock box
24. 0:42before it goes out. Layer five of the
25. 0:44OSI model is about the idea of
26. 0:46maintaining a session, an ongoing
27. 0:48conversation between your computer and
28. 0:50the server you're talking to. Think of
29. 0:52it like making the sure the person
30. 0:53you're talking to doesn't suddenly
31. 0:54forget who you are. Now we get to the
32. 0:57networking layers. Layer four is going
33. 0:59to wrap everything in TCP for reliable
34. 1:01delivery. It may add source ports like
35. 1:0354321 and destination port of 443 for
36. 1:05HTTPS and some sequence numbers. So it
37. 1:08basically sets ports and sequence
38. 1:09numbers. Layer three is going to add IP
39. 1:11routing information. So this is going to
40. 1:12be your IP address, the server's IP
41. 1:14address. Let's say it's 192.168.100
42. 1:17on your internal network and perhaps
43. 1:1993.184.26.34 216.34
44. 1:22for your server network like the IP
45. 1:24address that you're talking to. Layer
46. 1:26two adds MAC addressing and that's
47. 1:28mainly for local network, local Ethernet
48. 1:29connectivity. Finally, layer 1 is the
49. 1:32layer that actually converts everything
50. 1:34from electrical signals that travel
51. 1:35through your Ethernet or network cable
52. 1:37or the Wi-Fi radio waves. Now, your your
53. 1:39packet your network packet for from the
54. 1:41OSI model is like a Russian nesting
55. 1:43doll. Each layer is kind of wrapped
56. 1:45inside the next and as it travels across
57. 1:47the internet through routers that read
58. 1:49layer three switches that read layer two
59. 1:51and it finally reaches the web server.
60. 1:52Now the web server receives your packet
61. 1:54and processes it in reverse order just
62. 1:56like unwrapping all of those little
63. 1:58nesting dolls. So layer 1 converts
64. 2:00electrical signals back to data. Layer
65. 2:02two is going to look at the MAC headers.
66. 2:03Layer three is going to look at the IP
67. 2:04headers. Layer four is going to look at
68. 2:06the TCP headers. Layer five is going to
69. 2:08look at the session. Layer six is going
70. 2:10to handle decryption and formatting. And
71. 2:12finally, the highest layer, layer seven,
72. 2:13the application layer, it's going to
73. 2:14process your HTTP request and then it's
74. 2:16going to send back the web page
75. 2:17following the exact same path. So the
76. 2:19response is going to follow the same
77. 2:20seven layer journey back to your browser
78. 2:22where it's process also in a reverse
79. 2:23order. And this layered approach is
80. 2:25actually pretty clever. So your like
81. 2:26Wi-Fi router for example is going to
82. 2:27handle layers 1 through two. Your ISP is
83. 2:29going to handle layer three. Your brand
84. 2:30your browser is going to handle layers
85. 2:32four through 7. So each layer can be
86. 2:34optimized independently but still have
87. 2:35interoperability so that they can work
88. 2:37together. Understanding this layered
89. 2:39approach is super important for system
90. 2:40design because for example, load
91. 2:41balancers operate at different layers.
92. 2:43Some operate at layer four for fast
93. 2:44packet forwarding, others at layer 7 so
94. 2:46they can do intelligent application
95. 2:47routing. But firewalls can block layer
96. 2:503, layer four, layer 7, and each layer
97. 2:52provides specific services that
98. 2:53basically enable the layers above it to
99. 2:55function. So, we'll explore how load
100. 2:56balancers use these layers in another