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Posted 22 Aug 2008

Calculating the broadcast address for a subnet

, 22 Aug 2008
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How to calculate the broadcast address for a subnet.


This code returns the subnet broadcast address for a given IP address and subnet mask.

I needed it for a WOL function on a website which was in a different subnet and where the standard broadcast address didn't work.

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);

Here is the complete source 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);
    return IPAddress.Parse(arBroadCast[0] + "." + arBroadCast[1] + 
           "." + arBroadCast[2] + "." + arBroadCast[3]);


This article, along with any associated source code and files, is licensed under A Public Domain dedication


About the Author

Daniel Wernle
Software Developer Infineon Technologies
Austria Austria
.. was born
.. grew up

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Comments and Discussions

Question[My vote of 1] is better Pin
Shargon_855-Aug-11 22:50
memberShargon_855-Aug-11 22:50 
GeneralMy vote of 1 Pin
Acoustic5-Feb-09 10:15
memberAcoustic5-Feb-09 10:15 
GeneralMuch better solution Pin
Michal Brylka22-Aug-08 12:25
memberMichal Brylka22-Aug-08 12:25 

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