Hi again,
I just came across a huge clue. A friend had me look again at the java.net
properties. This one makes the test program work:
-Djava.net.preferIPv4Stack=true
Now, as to why suddenly Java was preferring the IPv6 stack, I have no idea.
On 2.11.10, Steve White wrote:
> Hi,
>
> A Java networking problem has arisen very recently on one of our servers,
> an Opeteron with Scientific Linux 5.5, running the distro Java without
> problems--until a week or so ago.
>
> The effect is that all Java apps have become unable to do DNS host name
> resolution, and throw an UnknownHostException. However nothing seems
> otherwise amiss with networking on this machine. All non-Java programs
> resolve outside host names fine.
>
> I wrote a small test program, attached. It works fine on other machines
> here. Fails on the server, with an IP address. But if I give it a valid
> IP number, or the name of the server itself, it succeeds.
>
> I have done security updates fairly regularly; this may have something to
> do with the problem, but I really don't know for sure.
>
> Also tried:
>
> * Cut the hosts file down to the bare minimum, and also the resolv.conf
> file and re-started networking. No improvement.
>
> * Logged in as various users. All show the same problem.
>
> * Cut down and exported all related environment variables to bare minimum
> (JAVA_HOME, PATH, *LIBRARY_PATH, etc),
> No effect.
>
> * Reversed the updates from last week, and re-booted with the
> previous kernel. No improvement.
>
> * Fiddled with various Java system properties, as in
> http://download.oracle.com/javase/6/docs/technotes/guides/net/properties.html
> Nothing seemed to help.
>
> * Installed a Java 1.5, built the test program with it, ran the test program
> under that. It failed just like the distro version.
>
> Any ideas?
>
> =========================================================
> To run the attached test
> javac nettest.java
> java nettest <hostname> <optional-port-number>
>
> --
> | - - - - - - - - - - - - - - - - - - - - - - - - -
> | Steve White +49(331)7499-202
> | E-Science Zi. 27 Villa Turbulenz
> | - - - - - - - - - - - - - - - - - - - - - - - - -
> | Astrophysikalisches Institut Potsdam (AIP)
> | An der Sternwarte 16, D-14482 Potsdam
> |
> | Vorstand: Prof. Dr. Matthias Steinmetz, Peter A. Stolz
> |
> | Stiftung privaten Rechts, Stiftungsverzeichnis Brandenburg: III/7-71-026
> | - - - - - - - - - - - - - - - - - - - - - - - - -
> import java.net.Socket;
>
> public class
> nettest
> {
> public static void
> main( String [] a )
> {
> if( a.length > 0 )
> {
> String host = a[0];
> int port = 80;
> if( a.length > 1 )
> {
> port = Integer.parseInt( a[1] );
> }
> try
> {
> Socket si = new Socket( host, port );
> System.out.println( "Success connecting to "
> + host );
> }
> catch( Exception e )
> {
> System.err.println( e.toString() );
> e.printStackTrace();
> }
> }
> else
> {
> System.err.println( "please provide host string" );
> }
> }
> }
--
| - - - - - - - - - - - - - - - - - - - - - - - - -
| Steve White +49(331)7499-202
| E-Science Zi. 27 Villa Turbulenz
| - - - - - - - - - - - - - - - - - - - - - - - - -
| Astrophysikalisches Institut Potsdam (AIP)
| An der Sternwarte 16, D-14482 Potsdam
|
| Vorstand: Prof. Dr. Matthias Steinmetz, Peter A. Stolz
|
| Stiftung privaten Rechts, Stiftungsverzeichnis Brandenburg: III/7-71-026
| - - - - - - - - - - - - - - - - - - - - - - - - -
|
