OSI Reference Model Layer Framing
Mnemonic Shortcut: "Please Do Not Throw Sausage Pizza Away"
| Layer | Name | Data Unit | Protocols & Hardware |
|---|---|---|---|
| L7 | Application | Data Payload | HTTP, DNS, SSH, FTP |
| L4 | Transport | Segments / Datagrams | TCP Port Bindings, UDP Streams |
| L3 | Network | Packets | IP Routing, ICMP, Routers |
| L2 | Data Link | Frames | MAC Addresses, VLAN Switches, ARP |
The TCP Three-Way Handshake
1. Client ➔ Server: Send SYN [Seq = X]
2. Server ➔ Client: Send SYN-ACK [Seq = Y, Ack = X + 1]
3. Client ➔ Server: Send ACK [Ack = Y + 1]
🧮 CIDR Subnet Calculator
Input any base network address and click compute to break out boundaries dynamically.