Feature/lab4

[03sano30]

Goal

Trace and debug network communication with QuickNotes using tcpdump, ss, dig, and outside-in debugging.

Changes

• Added submissions/lab4.md with:

  • Annotated packet capture (lab4-trace.txt) showing TCP handshake, HTTP request/response, and connection close
  • Five diagnostic commands (ss, ip route, mtr, dig, journalctl)
  • Outside-in debugging chain for a broken deploy (port conflict)
  • Blameless mini-postmortem

• Added lab4-trace.txt with full decoded capture

Testing

• Captured live traffic with sudo tcpdump while sending POST /notes
• Verified TCP three-way handshake: SYN → SYN-ACK → ACK
• HTTP request: POST /notes HTTP/1.1 with JSON body
• HTTP response: 201 Created with new note
• Connection teardown: FIN → FIN → ACK
• Reproduced bind: address already in use error and fixed it

Checklist

• Title is a clear sentence (≤ 70 chars)
• Commits are signed (git log --show-signature)
• submissions/lab4.md updated