(From 22025518, CN15-K67-UET)

🌐 SDN L3 Router with Anti-Loop & Real-Time Monitoring (POX/Mininet)

This project implements a complete Software-Defined Networking (SDN) Layer 3 Router abstraction using the POX controller framework. It manages routing across three distinct subnets interconnected in a loop (triangle) topology, prioritizing stability, performance, and security.

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This main branch is a all in one controller file for easily testing. If you want the clearly structure, switch to the Refactor-Code branch.

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1. ⚙️ Core Functionalities

This controller provides an end-to-end routing solution featuring:

• L3 Routing Abstraction: The OpenFlow switches (s1, s2, s3) are abstracted as ports of a single logical router, enabling communication between the 10.0.1.x, 10.0.2.x, and 10.0.3.x subnets.
• Anti-Loop Protection (BFS): Utilizes the openflow.discovery module to map the network's triangle topology and implements a Breadth-First Search (BFS) algorithm to find the shortest path, effectively preventing broadcast storms and routing loops.
• Reactive Flow Installation (Optimized Data Plane): Flows are installed only after the first packet of a conversation is processed (priority 50), significantly offloading the controller and improving network throughput for subsequent packets.
• Intra/Inter-Subnet ARP Handler: Correctly performs Proxy ARP for inter-subnet traffic and handles local ARP requests via secure flooding to avoid MAC confusion and router spoofing.
• Layer 4 Firewall (ACL): Proactively installs high-priority (100) firewall rules to drop unwanted traffic at the ingress switch.
• Real-Time Monitoring: A separate UDP-based monitor streams live traffic statistics (TCP, UDP, ICMP, Total Bytes) from the switch data planes.

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2. 🗺️ Topology and Setup

The network uses a stable triangle topology (s1-s2-s3-s1) to ensure redundancy, while the controller guarantees loop-free forwarding.

[Image of triangular network topology]

Subnet	Hosts	Gateway IP (Router MAC)	Switch DPID
A	h1, h2 (10.0.1.x)	10.0.1.1 (00:00:00:00:01:01)	1
B	h3, h4 (10.0.2.x)	10.0.2.1 (00:00:00:00:02:01)	2
C	h5, h6 (10.0.3.x)	10.0.3.1 (00:00:00:00:00:03:01)	3

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3. 🚀 Execution Instructions

The system requires two components running simultaneously: the Monitor Dashboard (Receiver) and the POX Controller (Sender/Router).

A. Prerequisites

1. Mininet: Installed and running (Tested on Mininet 2.3.0 or later). You can install the iso file of Ubuntu that already have mininet and POX installed here: https://github.com/mininet/openflow-tutorial/wiki/Installing-Required-Software
2. POX: Installed and accessible (Tested with POX 0.2.0 carp).
3. Ensure your topology file (multi_router_topo.py) is set up for the triangle topology and fixed ports (as discussed).

B. Startup Sequence (3 Terminals Required)

Terminal 1: Start the Monitoring Dashboard (UDP Receiver)

This terminal will display live statistics. (Run in the folder that have the file)

python monitor.py

Terminal 2: Start the POX Controller (Copy the prototype.py file into the /pox/pox/ext folder and go back to /pox/pox to run command)

cd pox
./pox.py openflow.discovery controller.py

Terminal 3: Start mininet with pre-configured topo (Run in the folder that have the file)

sudo mn --custom multi_router_topo.py --topo mytopo --controller remote --mac