Network Stack Challenge

All Games

OSI Model (7 layers)

Theoretical guideline — not directly implemented

7 — Application

6 — Presentation

5 — Session

4 — Transport

3 — Network

2 — Data Link

1 — Physical

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TCP/IP Stack (4–5 layers)

Practical standard — actually used on the internet

Application (L5–7)

↳ HTTP, HTTPS, DNS, TLS

↳ (incl. Presentation + Session)

Transport (TCP/UDP)

Internet / Network (IP)

Network Access (L1–2)

↳ Ethernet, Wi-Fi, MAC

Key insight: OSI is an abstract 7-layer reference model — it was designed to standardize how networks communicate. TCP/IP is the actual protocol suite that powers the internet, collapsing OSI layers 5–7 into one Application layer and layers 1–2 into one Network Access layer. In real deployments: your flask.opencodingsociety.com runs over TCP/IP on an AWS EC2 instance fronted by Nginx — no software directly "implements" OSI layers, but they help us reason about what happens at each level.

Bonus: MTU Frame Assembly Challenge (+50 pts if correct)

You're at Layer 4 — Transport. Before TCP segments leave, they're wrapped in an Ethernet frame. Select the correct byte size for each frame component:

Frame Header

IP Header

TCP Header

Max Payload

Frame Tail

Frame total: —

Daily

Daily round counts toward streak and overall progress.

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Streak

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OSI Model

Layer 7

Application

HTTP/S, DNS, Nginx, Flask

Layer 6

Presentation

TLS/SSL, Certbot

Layer 5

Session

WebSockets, sessions

Layer 4

Transport

TCP/UDP, ports, segments

Layer 3

Network

IP routing, AWS routing

Layer 2

Data Link

Ethernet frames, MAC

Layer 1

Physical

Cables, fiber, Wi-Fi

Select a question to see the active layer.