Port Scan

[G AMAR]

how to achive port scan using java sockets ?

[Michael Morris]

What kind of port scan? With normal Java sockets you can do a full TCP connect scan which is a noisey scan (the scanned system will know your IP address). Here's a quick and dirty example:

import java.net.*;
import java.io.*;
public class PortScan {
    public static void main(String[] args) throws IOException {
        InetAddress host = InetAddress.getLocalHost();
        int startPort = 1;
        int endPort = 1024;
        switch (args.length) {
        case 3 :
            endPort = Integer.parseInt(args[2]);
        // Fall thru
        case 2 :
            startPort = Integer.parseInt(args[1]);
        // Fall thru
        case 1 :
            host = InetAddress.getByName(args[0]);
        // Fall thru
        case 0 :
            break;
        default :
            System.err.println(
                "Usage: java PortScan [host] [startPort] [endPort]");
            System.exit(1);
        }
        if (startPort < 0 || startPort > 65535 ||
              endPort < 0 ||   endPort > 65535) {
            throw new IllegalArgumentException(
                          "PortScan: invalid port number");
        }
        System.out.println("Scanning host " + host.getHostName());
        for (int i = startPort; i <= endPort; i++) {
            System.out.print("Port " + i + ": ");
            try {
                Socket sock = new Socket(host, i);
            } catch (IOException e) {
                System.out.println("closed");
                continue;
            }
            System.out.println("open");
        }
    }
}

You can do something similar with a UDP scan, but the results are much less reliable, since there is no guarantee that a Port Unreachable ICMP packet will be returned.
Michael Morris