Protocols
A protocol is an agreement on the format and order of messages between two programs. The internet stacks them in layers: IP gets a packet to the right machine, TCP or UDP gets it to the right program, and application protocols such as HTTP, DNS and SSH define what the bytes mean.
| Layer | Protocols here | Job |
|---|---|---|
| Application | HTTP, HTTPS, DNS, SSH | Meaning of the messages |
| Transport | TCP, UDP | Ports, reliability, ordering |
| Internet | IP (in TCP/IP) | Addressing and routing between networks |
| Link | Ethernet, Wi-Fi | One hop on a local network |
Start with TCP/IP, then UDP, then the application protocols in any order.