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Packet Sniffer with Multi-Threaded Protocol Handling in C

The presented C code embodies a packet sniffer, leveraging multi-threading for concurrent processing of diverse Ethernet frame types. The program captures packets from a user-specified Ethernet interface, employing a frameio class for raw network access and message queues to distinguish and handle IP and ARP frames. The code defines a structure for Ethernet frames and features functions to display packet content in hexadecimal format. With dedicated threads for the protocol loop, IP frame processing, and ARP frame handling, the program orchestrates real-time packet analysis. Notably, user interaction is facilitated for specifying the target Ethernet interface, ensuring versatility and practicality in network analysis and diagnostics.

Efficient Multi-Threaded Packet Sniffer in C for Advanced Network Analysis

The showcased C code constitutes a robust packet sniffer that adeptly manages Ethernet frames through multi-threading. Specifically designed to handle IP and ARP protocols concurrently, the program employs the frameio class and message queues for seamless packet categorization and processing. With a structured representation of Ethernet frames and functions for displaying packet content, this code provides a comprehensive framework for real-time network analysis. Students seeking assistance with their C assignments can find value in exploring this implementation, gaining insights into packet manipulation, threading, and protocol-specific handling. The interactive input for specifying the Ethernet interface enhances user engagement, making it a practical resource for learning and implementing network diagnostics in C.

Block 1: Header and Global Variables

#include "frameio.h" #include "util.h" #include #include #include #include #include char ethernet_name[1024]; // ethernet name for capturing packet frameio net; // gives us access to the raw network message_queue ip_queue; // message queue for the IP protocol stack message_queue arp_queue; // message queue for the ARP protocol stack
  • This block includes necessary header files and defines global variables.
  • ethernet_name: A buffer to store the name of the Ethernet interface for packet capture.
  • net: An instance of the frameio class that provides access to the raw network.
  • ip_queue and arp_queue: Message queues for the IP and ARP protocol stacks, respectively.

Block 2: Structure Definition

struct ether_frame { octet dst_mac[6]; // destination MAC address octet src_mac[6]; // source MAC address octet prot[2]; // protocol (or length) octet data[1500]; // payload };
  • Defines a structure ether_frame to represent an Ethernet frame with destination MAC, source MAC, protocol, and payload.

Block 3: Packet Display Function

void display_packet(octet buf[]) { // Function to display the hexadecimal representation of a packet }
  • ¬†display_packet function prints the hexadecimal representation of a packet.

Block 4: Main Packet Capturing Loop

void *protocol_loop(void *arg) { // Main packet capturing loop }
  • A pthread function (protocol_loop) for the main packet capturing loop.
  • Captures Ethernet frames, filters them based on protocol type (IP or ARP), and sends them to the corresponding message queues.

Block 5: IP Protocol Handling Function

void *ip_protocol_loop(void *arg) { // Function to process IP protocol frames }
  • A pthread function (ip_protocol_loop) for processing IP protocol frames.
  • Displays information about the IP frame, queues a timer event, and prints a message when the timer event fires.

Block 6: ARP Protocol Handling Function

void *arp_protocol_loop(void *arg) { // Function to process ARP protocol frames }
  • A pthread function (arp_protocol_loop) for processing ARP protocol frames.
  • Displays information about ARP frames.

Block 7: Thread Initialization and Main Function

pthread_t loop_thread, arp_thread, ip_thread; int main() { // Main function }
  • Initializes pthreads for the main packet capturing loop (loop_thread), ARP processing (arp_thread), and IP processing (ip_thread).

Block 8: Interface Initialization and Thread Execution

rc = net.open_net(ethernet_name); // Interface initialization pthread_create(&loop_thread,NULL,protocol_loop,NULL); pthread_create(&arp_thread,NULL,arp_protocol_loop,NULL); pthread_create(&ip_thread,NULL,ip_protocol_loop,NULL); // Thread creation pthread_join(loop_thread, NULL); // Main thread waits for the packet capturing loop to finish return 0; }
  • Initializes the network interface and checks for errors.
  • Creates pthreads for the different protocol processing functions.
  • The main thread waits for the protocol_loop thread to finish using pthread_join.


In summary, this C program serves as a rudimentary network packet sniffer, capturing Ethernet frames from a specified interface. Leveraging pthreads for concurrent execution, it manages distinct threads for the primary packet capturing loop, IP protocol processing, and ARP protocol processing. The frameio class provides raw network access, while message queues facilitate communication between threads. The program's modular design enhances maintainability and extensibility. Upon initialization, the user inputs the Ethernet interface, and the main thread orchestrates the concurrent threads. This minimalist packet sniffer offers a foundation for understanding network protocol handling and multithreading in a compact yet comprehensive manner.