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Learning the OSI model (and TCP/IP model)

Just one of the things I'm learning. https://github.com/hchiam/learning

OSI model = Open Systems Interconnection model.

Simple practical perspective

My summary of "Practical Networking" videos https://www.youtube.com/watch?v=LkolbURrtTs and https://www.youtube.com/watch?v=0aGqGKrRE0g:

  1. Physical layer = bits ("physics")
  2. Data Link layer = hops (MACs, e.g. router MACs). Add header to data = data is now called a "frame".
  3. Networking layer = ends (IPs, e.g. server IPs). Add header to data = data is now called a "packet".
  4. Transport layer = services (e.g. ports/programs, like at TCP/UDP/etc ports). Add header to data = data is now called a "segment".
  5. 5+6+7 Application layer = data

7 layers

Host layers:

Media layers:

The process goes from the top-level concerns down to the bottom-level and back up:

7 -> 6 -> 5 -> 4 -> 3 -> 2 -> 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7

Here's a list of which parts of the OSI model different protocols correspond to: https://en.wikipedia.org/wiki/OSI_model#Comparison_to_other_networking_suites (note that some things like TCP/IP and security span different layers).

Further reading

TCP/IP model:

  1. Process/App Layer (HTTP, HTTPS, FTP, SMTP, SSH, DNS, DHCP, ...)
    • port
  2. Host-to-Host/Transport Layer (TCP, UDP)
    • packets (and reassembly meta info)
  3. Internet Layer (IP, ARP, RARP, IGMP)
    • add source and destination IP addresses
  4. Network Access/Link Layer (hardware)
    • assign MAC addresses of sender and receiver to each packet
    • convert to 1's and 0's