Step-by-Step: Create a C Port Scanner Guide

Building a Port Scanner in C

Explore our comprehensive guide on how to write a port scanner in C, delving into essential C programming concepts and gaining valuable insights into network security practices. Whether you're a beginner or looking for advanced tips, our step-by-step guide is here to help with your C assignment, ensuring you master both the fundamentals of C and the intricacies of network scanning.

Prerequisites

Before we dive in, here are a few things you'll need:

A C Compiler: Make sure you have a C compiler installed on your system. GCC is a popular choice.
Basic C Knowledge: You don't need to be an expert, but some familiarity with C programming will be helpful.

Understanding the Port Scanning Process

Our port scanner will work by attempting to establish connections to a range of ports on a target system. If a connection is successful, the port is considered open; otherwise, it's closed.

Here are the key steps we'll follow in our C program:

Parsing Command Line Arguments: We'll parse command line arguments to specify the target IP address and the range of ports to scan.
Creating a Socket: We'll create a socket, a fundamental networking concept that allows us to communicate over the network.
Iterating Through Ports: Our program will loop through the specified range of ports, checking each one.
Attempting Connections: We'll try to connect to each port to determine whether it's open or closed.
Reporting Results: Finally, we'll report the status of each port.

The C Code

Below, you'll find the C code for our basic port scanner, along with explanations for each section. We'll guide you through the code so you can understand how it works and modify it as needed for your projects.

#include 
#include 
#include 
#include 
#include 
#include 
#include 
int main(int argc, char *argv[]) {
// Check for correct number of command line arguments
if (argc != 4) {
printf("Usage: %s   \n", argv[0]);
return 1;
}
// Parse command line arguments
char *target_ip = argv[1];
int start_port = atoi(argv[2]);
int end_port = atoi(argv[3]);
// Loop through the specified range of ports
for (int port = start_port; port <= end_port; port++) {
// Create a socket
int sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0) {
perror("socket");
return 1;
}
// Set up the sockaddr_in structure
struct sockaddr_in target_addr;
target_addr.sin_family = AF_INET;
target_addr.sin_port = htons(port);
inet_pton(AF_INET, target_ip, &target_addr.sin_addr);
// Attempt to connect to the port
if (connect(sockfd, (struct sockaddr *)&target_addr, sizeof(target_addr)) == 0) {
printf("Port %d is open.\n", port);
} else {
// Port is closed
// perror("connect"); // Uncomment this line for debugging
}
// Close the socket
close(sockfd);
}
return 0;
}

Usage

To use our port scanner, simply compile the code using your C compiler and execute it from the command line with the following syntax:

```
./port_scanner   
```

Replace ` ` with the IP address of your target system, and specify the range of ports you want to scan with ` ` and ` ` .

Conclusion

Writing a basic port scanner in C is a great way to learn about network programming. However, please remember to use this tool responsibly and only on systems for which you have proper authorization. Unauthorized port scanning can be illegal and unethical. It's essential to adhere to ethical guidelines and obtain the necessary permissions when conducting any form of network exploration or security testing.

How to Write a Program to Port Scanner in C