How the internet routes packets

Lesson 0.5 covered who talks (client/server). This lesson covers how bytes travel between them.

Layers (simplified)

Your curl command
      │
      ▼ DNS (name → IP)
      ▼ TCP (reliable port :8081)
      ▼ HTTP (method, headers, JSON body)
      ▼ HTTP response back

On localhost you skip wide-area routing, but the same stack applies — useful when you later debug real networks.

playstepchallengeinstructor

Trace packetPause

1

ApplicationDNS lookup

localhost → 127.0.0.1 (or ::1)

2

TransportTCP handshake

SYN → SYN-ACK → ACK on port 8081

3

ApplicationHTTP request line

POST /webhooks/hello HTTP/1.1

4

ApplicationHTTP headers

Host: localhost:8081 · Content-Type: application/json · Content-Length: …

5

ApplicationHTTP body

JSON bytes cross the socket as raw payload

6

ApplicationHTTP response

HTTP/1.1 200 OK · Content-Type: application/json · body

curl -v is your X-ray

Verbose mode prints each phase:

curl -v -X POST http://localhost:8081/webhooks/hello \
  -H 'Content-Type: application/json' \
  -d '{"source":"github"}'

Look for Connected to, > POST, < HTTP/1.1 200.

Team Radar tie-in

Every GitHub webhook simulation crosses this path before Kafka ever sees a message. If TCP fails, ingestion logs never run.

Teach-back prompt

Which hop is still HTTP if you switch port 8081 → 8443 with HTTPS?