🌐 IPv4 Router Data Plane Implementation

A complete implementation in C of an IPv4 Router Data Plane, simulating the essential packet-processing logic of a real network router. This project handles Ethernet frames, IPv4 forwarding, ARP resolution, and ICMP message generation, with a strong focus on performance and correctness.

At its core, the routing process is optimized using a Trie (Prefix Tree) to efficiently perform Longest Prefix Match (LPM) lookups.

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🚀 Overview

This router processes network traffic by:

• Receiving raw Ethernet frames
• Parsing and validating IPv4 packets
• Determining optimal routes
• Resolving MAC addresses dynamically
• Generating ICMP responses when required

The system closely mimics how real routers operate at the data plane level.

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⚙️ Core Functionalities

📦 IPv4 Packet Forwarding

• Validates IPv4 headers:

  • Checksum verification
  • TTL decrement

• Performs Longest Prefix Match (LPM) on the routing table

• Determines next-hop IP address

• Updates Ethernet headers:

  • Source MAC
  • Destination MAC

• Forwards packets to the appropriate interface

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🔁 ARP (Address Resolution Protocol)

• Maintains a dynamic ARP cache

• If MAC address is unknown:

  • Sends ARP Request (ARP_REQ)
  • Queues the packet

• On receiving ARP Reply (ARP_REP):

  • Updates ARP cache
  • Dequeues and forwards pending packets

• Responds to ARP requests targeting router interfaces

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📡 ICMP (Internet Control Message Protocol)

Handles key ICMP message types:

• Echo Reply (ICMP_ECHO_REP)

  • Responds to ping requests directed at router interfaces

• Time Exceeded (ICMP_TIME_EXC)

  • Triggered when TTL reaches 0 or 1

• Destination Unreachable (ICMP_DEST_UNREACH)

  • Sent when no valid route exists

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🌲 Optimized Routing Table (Trie)

• Routing tables (rtable0.txt, rtable1.txt) are parsed at startup

• Stored in a Trie (Prefix Tree) structure

• Enables:

  • Extremely fast Longest Prefix Match
  • Lookup complexity ≈ O(1) relative to fixed 32-bit IPv4 length

✔ Eliminates inefficient linear searches ✔ Scales efficiently with large routing tables

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📁 Project Structure

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├── router.c            # Main packet processing loop
├── include/            # Header files (Ethernet, IP, ARP, ICMP)
├── lib/                # Utility libraries and data structures
├── rtable0.txt         # Routing table (instance 0)
├── rtable1.txt         # Routing table (instance 1)
├── checker/            # Automated testing environment (Mininet)
└── README.md           # Project documentation

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💻 Build & Run

🔧 1. Compilation

make

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🧪 2. Testing the Router

The project uses a virtual network environment to simulate hosts and router interfaces.

• The checker script:

  • Builds network topology (using Mininet)

  • Runs tests like:

    • ping
    • traceroute
    • ARP scenarios
    • Packet forwarding validation

sudo ./checker/checker.sh

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🧪 Testing Environment

The checker/ directory provides:

• Automated validation scripts
• Virtual network topologies
• Traffic simulation scenarios

✔ Ensures correctness of:

• Routing logic
• ARP handling
• ICMP responses

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🎯 Design Goals

• High-performance packet forwarding
• Accurate simulation of router data plane behavior
• Efficient routing using Trie-based LPM
• Modular and clean C implementation
• Realistic networking environment testing

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📌 Future Improvements

• Support for dynamic routing protocols (e.g., OSPF, RIP)
• IPv6 compatibility
• Advanced queue management (QoS)
• Multithreaded packet processing
• Enhanced ARP cache policies (timeouts, eviction)

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📜 License

This project is open-source and available under the MIT License.

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👨‍💻 Author

Developed as a systems programming project focused on:

• Computer Networks
• Low-level packet processing
• Data structures for performance optimization

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