So it begins

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🚨 What’s the Problem?

Some of the most dangerous attacks don’t make a lot of noise. Instead, they quietly scan your network or impersonate other devices to intercept your traffic. Two examples of this are:

• SYN scanning, where a device sends a burst of TCP connection attempts to find open ports.

• ARP spoofing, where a machine sends fake ARP replies to hijack traffic.

To detect this kind of stealthy behavior, a Python script was built to analyze .pcap (packet capture) files and automatically flag suspicious patterns.
You can download a .pacp file from the internet.

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🔧 How It Works

The script uses the dpkt library to read through the captured packets and look for:

• SYN scanners: Any IP that sends more than 5 SYN packets (with no ACK flag), and receives very few or no SYN-ACK responses.

• ARP spoofers: Any MAC address that sends multiple ARP replies that were never requested.

This helps identify machines that might be probing the network or impersonating others.

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🧪 Real Example (Simplified)

When analyzing a captured file, the tool produces output like this:

SYN scanners:
128.3.23.117
128.3.23.5

ARP spoofers:
80:0b:98:3b:b9:ec
7c:d1:c3:94:9e:b8

In this case:

• The IPs 128.3.23.117 and 128.3.23.5 were flagged for sending multiple SYNs without completing handshakes — a common sign of port scanning.

• The MACs 80:0b:98:3b:b9:ec and 7c:d1:c3:94:9e:b8 sent over 5 ARP replies each, none of which were requested — a red flag for spoofing.

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💻 How to Set It Up (with Virtual Environment)

To keep your environment clean and avoid version conflicts, it’s best to use a Python virtual environment:

1. Create a Virtual Environment

python3 -m venv venv

2. Activate the Environment

• On Linux/macOS:

    source venv/bin/activate
  

• On Windows:

    venv\Scripts\activate
  

You’ll know it worked if your terminal shows (venv) before the prompt.

3. Install Dependencies

pip install dpkt

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▶️ Run the Detector

With everything set up, run the script:

python3 detector.py sample.pcap

The tool will scan the packet file and print any suspicious IP and MAC addresses it detects.

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🧠 Why It Matters

This tool makes it easy to catch early signs of malicious activity hidden in network traffic. Whether you're monitoring a real system or learning about cybersecurity, analyzing packets gives you valuable insights into what’s really going on under the hood.
A light take on network security. Till next time folks happy coding.