IPv4 vs. IPv6 question

Question

I have a machine that I believe is running only IPv6 and here is why, when I try to compile and run this example I found on the internet:
import java.net.*;
import java.io.*;
public class ip
public static void main ( String[] args ) throws IOException
String hostname;
BufferedReader input = new BufferedReader ( new InputStreamReader(System.in) );
System.out.print("\n");
System.out.print("Host name: ");
hostname = input.readLine();
try
InetAddress ipaddress = InetAddress.getByName(hostname);
System.out.println("IP address: " + ipaddress.getHostAddress());
catch ( UnknownHostException e )
System.out.println("Could not find IP address for: " + hostname);
When I run the example and type in liveupdate.symantec.com I get this from the program:
Host name: liveupdate.symantec.com
Could not find IP address for: liveupdate.symantec.com
If I run it like this java –Djava.net.preferIPv4Stack=true ip I get the following results:
Host name: liveupdate.symantec.com
IP address: 207.148.159.25
Can someone here help explain what the system property java.net.preferIPv4Stack=true means? And which way should I change the code so that it will work without having to set this system property?
Thank you very much for your time

Answer 1

Can someone here help explain what the system property java.net.preferIPv4Stack=true means?I answered that. It tells Java to prefer the IPv4 stack in situations like yours where both are available. See [IPv6 Support|http://java.sun.com/j2se/1.5.0/docs/guide/net/ipv6_guide/index.html] for more info on IPv6 in Java. See also [Networking Properties|http://java.sun.com/j2se/1.5.0/docs/guide/net/properties.html].
And which way should I change the code so that it will work without having to set this system property?In this case you could try InetAddress.getAllByName() and traversing the result array until you find an IPv4 address. Or you could set that property in the code rather than the command line.
I have no idea about IPv6 configuration on your machine, it's dependent on everything except Java.