Project 12: TCP/IP Stack in Userspace (Network Programming Mastery)

A userspace TCP/IP stack that handles Ethernet frames, IP packets, and TCP connections—bypassing the kernel’s network stack entirely.

Quick Reference

Attribute Value
Primary Language Rust
Alternative Languages C (traditional approach)
Difficulty Level 5: Master
Time Estimate 1-2 months
Knowledge Area Networking / Protocol Implementation / Raw Sockets
Tooling tun/tap interfaces, raw sockets
Prerequisites Strong networking fundamentals, all prior Rust projects

What You Will Build

A userspace TCP/IP stack that handles Ethernet frames, IP packets, and TCP connections—bypassing the kernel’s network stack entirely.

Why It Matters

This project builds core skills that appear repeatedly in real-world systems and tooling.

Core Challenges

  • Parsing and constructing network packets → maps to byte-level manipulation with types
  • Implementing TCP state machine → maps to enums and pattern matching
  • Handling checksums and byte order → maps to safe low-level operations
  • Managing connection state safely → maps to ownership for resource management

Key Concepts

  • TCP state machine: “TCP/IP Illustrated, Volume 1” Chapters 17-24 - Stevens
  • Network byte order: “Computer Networks” Chapter 5 - Tanenbaum
  • Raw sockets and TUN/TAP: “The Linux Programming Interface” Chapter 58 - Kerrisk
  • Bitfield parsing in Rust: “Programming Rust, 2nd Edition” - Jim Blandy

Real-World Outcome

$ sudo cargo run -- --interface tun0
🌐 RustTCP - Userspace TCP/IP Stack
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Interface: tun0
IP: 192.168.1.100/24

Listening on port 80...

[TCP] SYN received from 192.168.1.1:54321
[TCP] -> SYN-ACK sent
[TCP] ACK received - Connection ESTABLISHED

[HTTP] Request: GET / HTTP/1.1
[HTTP] Response: 200 OK (342 bytes)

[TCP] FIN received
[TCP] -> FIN-ACK sent
[TCP] Connection CLOSED

Statistics:
  Packets received: 1,247
  Packets sent: 1,189
  TCP connections: 12
  Checksum errors: 0
  Retransmissions: 3

Implementation Guide

  1. Reproduce the simplest happy-path scenario.
  2. Build the smallest working version of the core feature.
  3. Add input validation and error handling.
  4. Add instrumentation/logging to confirm behavior.
  5. Refactor into clean modules with tests.

Milestones

  • Milestone 1: Minimal working program that runs end-to-end.
  • Milestone 2: Correct outputs for typical inputs.
  • Milestone 3: Robust handling of edge cases.
  • Milestone 4: Clean structure and documented usage.

Validation Checklist

  • Output matches the real-world outcome example
  • Handles invalid inputs safely
  • Provides clear errors and exit codes
  • Repeatable results across runs

References

  • Main guide: LEARN_RUST_DEEP_DIVE.md
  • “TCP/IP Illustrated, Volume 1” by W. Richard Stevens