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  1. JDK
  2. JDK-7158636

InterfaceAddress.getBroadcast() returns invalid broadcast address on WLAN

    Details

    • Subcomponent:
    • Resolved In Build:
      b38
    • CPU:
      x86
    • OS:
      windows_7
    • Verification:
      Verified

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        Description

        FULL PRODUCT VERSION :
        java version "1.7.0_02"
        Java(TM) SE Runtime Environment (build 1.7.0_02-b13)

        ADDITIONAL OS VERSION INFORMATION :
        Microsoft Windows [versie 6.1.7601]

        A DESCRIPTION OF THE PROBLEM :
        For an UDP application I want to send a packet to the network broadcast address.

        java.net.InterfaceAddress has the method getBroadcast() to retrieve this information. However, on a wireless connection this functionality is broken.

        getBroadcast() always returns 0.0.0.0 on the wireless interface, although it works correctly for the wired interface.

        I can reproduce this problem on multiple laptops.

        Trying to work around this by applying the subnetmask to the ip myself is impossible, because getNetworkPrefixLength() returns -1 on a WLAN connection.

        If I connect to laptop to the same network using a cable instead of using WiFi, Java returns the correct information about the broadcast address on the wired interface.

        STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
        1. Execute source code attached as "Source code for an executable test case" on a laptop connected to WiFi / WLAN.
        2. Output shows that the broadcast address is wrong

        EXPECTED VERSUS ACTUAL BEHAVIOR :
        EXPECTED -
        The names of the network interfaces and the ip can be different:

        {{net3}}
        145.89.X.X: 145.89.131.255 | 22

        {{eth3}}
        145.89.X.X: 145.89.131.255 | 22
        ACTUAL -
        Instead of the expected result java.net.InterfaceAddress.getBroadcast() returns 0.0.0.0 and getNetworkPrefixLength() returns -1 for the WiFi adapter only. As seen here, the wired interface returns the correct information.

        {{net3}}
        145.89.X.X: 0.0.0.0 | -1

        {{eth3}}
        145.89.X.X: 145.89.131.255 | 22

        REPRODUCIBILITY :
        This bug can be reproduced always.

        ---------- BEGIN SOURCE ----------
        import java.net.Inet6Address;
        import java.net.InterfaceAddress;
        import java.net.NetworkInterface;
        import java.util.Enumeration;

        public class BugDemonstrator
        {

            public static void main(String[] args) throws Exception
            {
                Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
                while(interfaces.hasMoreElements())
                {
                    NetworkInterface networkInterface = interfaces.nextElement();
                    if (networkInterface.isLoopback() || (!networkInterface.isUp()))
                        continue; // Ignore loopback and interfaces that are down
                    
                    System.out.println("== "+networkInterface.getName()+" ==");
                    for (InterfaceAddress interfaceAddress : networkInterface.getInterfaceAddresses())
                    {
                        if(interfaceAddress.getAddress() instanceof Inet6Address)
                            continue; //IPv6 doesn't have broadcast adresses

                        String ipAddress = interfaceAddress.getAddress().getHostAddress();
                        String broadcastAddress = interfaceAddress.getBroadcast().getHostAddress();
                        short networkPrefixLength = interfaceAddress.getNetworkPrefixLength();

                        System.out.println(ipAddress+": "+broadcastAddress+" | "+networkPrefixLength);
                    }
                    System.out.println();
                }
            }

        }
        ---------- END SOURCE ----------

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                • Assignee:
                  khazra Kurchi Subhra Hazra
                  Reporter:
                  webbuggrp Webbug Group
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