Calculate the Broadcastaddress for Subnet

Introduction

This code returns the Subnet-Broadcast-Address for a given IP-Address and Subnetmask.

I needed it for a WOL Funktion on a website which was in an different subnet and where the standard broadcastaddress didn't worked out.

Using the code

This function is quite easy and could be used for example in an UdpClient Object like this.

 UdpClient client = new UdpClient();
 client.Connect(CalculateBroadCastAddress(ip,nm).ToString(), 40000); 

Code:

using System.Net.Sockets;
using System.Net;
using System.Globalization;
using System.Collections;

           
        static IPAddress CalculateBroadCastAddress(IPAddress currentIP, IPAddress ipNetMask)
        {
            string[] strCurrentIP = currentIP.ToString().Split('.');
            string[] strIPNetMask = ipNetMask.ToString().Split('.');

            ArrayList arBroadCast = new ArrayList();

            for (int i = 0; i < 4; i++)
            {
                int nrBCOct = int.Parse(strCurrentIP[i]) | (int.Parse(strIPNetMask[i]) ^ 255);
                arBroadCast.Add(nrBCOct.ToString());
            }
            return IPAddress.Parse(arBroadCast[0] + "." + arBroadCast[1] + "." + arBroadCast[2] + "." + arBroadCast[3]);
        }         

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