The OSI & TCP/IP layers, animated.
Two famous models describe how data turns into bits on the wire. Watch a packet get wrapped layer by layer at the sender, ride the wire, then unwrap layer by layer at the receiver — and see how OSI's 7 layers and TCP/IP's 4 layers describe the same thing.
OSI seven-layer model and TCP/IP four-layer model animated tutorial. Encapsulation walkthrough from application data through Ethernet frame, then decapsulation at the receiver. Covers headers for TCP, IP, and Ethernet plus port, IP-address, and MAC-address concepts.A packet wrapped layer by layer at the sender, transmitted, then unwrapped layer by layer at the receiver. Watch the headers stack and peel off.
- ·Rough sense of what an IP address is
- ·Have heard of TCP and UDP, even vaguely
- ·Helpful: the URL flow lesson — it shows TCP and IP in context
Name every OSI layer in order. Explain what header each layer adds, and why IP and MAC addresses serve different purposes.
pace: 8 minutes
// 7 OSI layers, top to bottom: 7 Application, 6 Presentation, 5 Session, 4 Transport, 3 Network, 2 Data Link, 1 Physical. TCP/IP groups layers 5–7 as "Application" and layers 1–2 as "Link".
Two models, same packet
Two famous models describe the same thing: how data turns into bits on the wire. OSI splits it into 7 layers (1 = Physical at the bottom, 7 = Application at the top). TCP/IP groups them into 4 (Link, Internet, Transport, Application). Same packet, different labels.
Each layer only talks to the layers next to it. The Transport layer knows nothing about the cable or the Wi-Fi chip. The Network layer knows nothing about your TCP sequence numbers. That isolation is why you can replace one part of the stack — swap Ethernet for Wi-Fi, swap TCP for QUIC, swap HTTP for SSH — without rewriting the rest.
$L7 Application$L6 Presentation$L5 Session$L4 Transport$L3 Network$L2 Data Link$L1 Physical$TCP/IP : Link$TCP/IP : Internet$TCP/IP : Transport$TCP/IP : Application$tcpdump -i any -nn$ss -tlnp$ip route$ip neighbor$ip -s linkWhich OSI layer adds the source and destination IP addresses?
Why does a packet need BOTH an IP address and a MAC address?
Which best describes the difference between TCP and UDP?
At which OSI layers do switches and routers operate?
These aren't graded — they're just for active recall, which is what actually makes the lesson stick.
Network tools
ping (L3), traceroute (L3), DNS lookup (L7), MTU check (L2/L3), and more. Each one operates at a specific layer — try them while picturing where in the stack you are.
keep going — these pair well with what you just learned.
What happens when you type a URL?
The most-asked interview question, animated. Five chapters: DNS → TCP → TLS → HTTP → Render. Step through each at your own pace.
DNS deep dive
Beyond the basics: recursive vs iterative, cache layers, TTLs, glue records, and what `dig +trace` actually shows.
NAT and routing
How packets cross networks. Source NAT, destination NAT, conntrack, routing tables — visualized with real IPs.