Question

I’ve started to do some basic network programming.

I have read/written my own programs using TcpClient and TcpListener and that has worked fine.

However, the application I am working on now works a bit differently.

I want to set up a program that listens for tcp/ip packets without having to connect.

For example, have a packet sending app send a packet to my program with the appropriate ip add and port number.

I have also looked into using Sharppcap and packet.net but all of the examples I’ve found only listens on devices found locally (no opportunity to set parameters such as port number and ip add).

Does anyone have a suggestion on how to go about doing this?

Answer 1

You should look at using the UDP protocol instead of TCP/IP.

http://en.wikipedia.org/wiki/User_Datagram_Protocol

Here is the code for the client:

using System.Net;
using System.Net.Sockets;

...

/// <summary>
/// Sends a sepcified number of UDP packets to a host or IP Address.
/// </summary>
/// <param name="hostNameOrAddress">The host name or an IP Address to which the UDP packets will be sent.</param>
/// <param name="destinationPort">The destination port to which the UDP packets will be sent.</param>
/// <param name="data">The data to send in the UDP packet.</param>
/// <param name="count">The number of UDP packets to send.</param>
public static void SendUDPPacket(string hostNameOrAddress, int destinationPort, string data, int count)
{
    // Validate the destination port number
    if (destinationPort < 1 || destinationPort > 65535)
        throw new ArgumentOutOfRangeException("destinationPort", "Parameter destinationPort must be between 1 and 65,535.");

    // Resolve the host name to an IP Address
    IPAddress[] ipAddresses = Dns.GetHostAddresses(hostNameOrAddress);
    if (ipAddresses.Length == 0)
        throw new ArgumentException("Host name or address could not be resolved.", "hostNameOrAddress");

    // Use the first IP Address in the list
    IPAddress destination = ipAddresses[0];            
    IPEndPoint endPoint = new IPEndPoint(destination, destinationPort);
    byte[] buffer = Encoding.ASCII.GetBytes(data);

    // Send the packets
    Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);           
    for(int i = 0; i < count; i++)
        socket.SendTo(buffer, endPoint);
    socket.Close();            
}