Introduction Analyzing network traffic is a core skill for cybersecurity professionals and network administrators. While Wireshark is the standard GUI tool for this task, software developers often need to analyze traffic programmatically.
For .NET developers, Pcap.Net is a powerful wrapper for WinPcap/Npcap. It allows you to capture, inject, and analyze network packets directly within C# or VB.NET applications. This article provides a step-by-step guide to setting up Pcap.Net and parsing network traffic. Prerequisites and Setup
Before writing code, you must configure your development environment to interface with your network hardware.
Install Npcap: Download and install Npcap (or WinPcap) on your machine. Ensure you check the box to install it in “API-compatible mode” during setup.
Add NuGet Package: Open your .NET project and install the Pcap.Net.x64 or Pcap.Net.x86 package via the NuGet Package Manager.
Set Platform Target: Pcap.Net requires a specific architecture. Change your project build settings from Any CPU to x64 or x86 to match your installed NuGet package. Step 1: Listing Available Network Interfaces
To capture traffic, you must first identify and select the correct network interface card (NIC).
using System; using System.Collections.Generic; using PcapDotNet.Core; class Program { static void Main() { // Retrieve the device list from the local machine IList Use code with caution. Step 2: Opening a Device for Capturing
Once you select an interface, open a packet communicator session. This requires defining the snapshot length (buffer size) and putting the card into promiscuous mode to capture all traffic.
// Select the first adapter PacketDevice selectedDevice = allDevices[0]; // Open the device // 65536 ensures the whole packet is captured // PacketDeviceOpenAttributes.Promiscuous enables promiscuous mode // 1000 ms read timeout using (PacketCommunicator communicator = selectedDevice.Open(65536, PacketDeviceOpenAttributes.Promiscuous, 1000)) { Console.WriteLine(“Listening on ” + selectedDevice.Description + “…”); // Start the capture loop communicator.ReceivePackets(0, PacketHandler); } Use code with caution. Step 3: Filtering Traffic (BPF)
Capturing every packet can overwhelm your application. You can use Berkeley Packet Filters (BPF) to isolate specific traffic, such as HTTP or a specific IP address, before processing.
// Compile the filter to only capture TCP traffic on port 80 using (PacketCommunicator communicator = selectedDevice.Open(65536, PacketDeviceOpenAttributes.Promiscuous, 1000)) { communicator.SetFilter(“tcp port 80”); communicator.ReceivePackets(0, PacketHandler); } Use code with caution. Step 4: Parsing and Analyzing Packets
The PacketHandler method triggers every time a packet passes through the filter. Pcap.Net features built-in extractors that easily break down complex protocols like Ethernet, IPv4, TCP, and UDP.
using PcapDotNet.Packets; using PcapDotNet.Packets.IpV4; using PcapDotNet.Packets.Transport; private static void PacketHandler(Packet packet) { // Print timestamp Console.WriteLine(\("{packet.Timestamp.ToString("yyyy-MM-dd HH:mm:ss.ffffff")}"); // Extract IPv4 Layer IpV4Datagram ip = packet.Ethernet.IpV4; if (ip != null) { Console.WriteLine(\)“Source IP: {ip.Source} -> Destination IP: {ip.Destination}”); } // Extract TCP Layer TcpDatagram tcp = ip?.Tcp; if (tcp != null) { Console.WriteLine(\("Ports: {tcp.SourcePort} -> {tcp.DestinationPort}"); Console.WriteLine(\)“Sequence Number: {tcp.SequenceNumber}”); } Console.WriteLine(new string(‘-’, 50)); } Use code with caution. Conclusion
Pcap.Net bridges the gap between deep network diagnostics and the .NET runtime. By combining interface selection, BPF filtering, and strongly-typed packet extraction, you can build custom firewalls, diagnostic suites, or automated intrusion detection tools tailored to your infrastructure needs.
If you’d like to expand this article, let me know if you want to include: How to read and write offline PCAP files Deep packet inspection of HTTP or DNS payloads Performance optimization tips for high-throughput networks
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