InetAddress.isReachable(nif, ttl, timeout) throws a ConnectException on redhat advanced server 2.1 with an "Invalid argument" message. The same test passes on redhat 8.0 . The problem seems to be in the loopback interface of RH AS 2.1 .

Steps to reproduce the problem:

1. Compile and run the code given below on a Redhat Advanced Server 2.1 machine.
2. The error is thrown.

-----------------------BEGIN CODE------------------------
import java.util.*;
import java.net.*;
import java.io.*;

public class NIFBug{
        public static void main(String args[]){
                NetworkInterface nif = null;
                InetAddress sqeweb = null;
                Enumeration <NetworkInterface> nifEnum = null;

                try{
                        sqeweb = InetAddress.getByName("sqeweb.sfbay.sun.com");
                }catch (UnknownHostException uhe){
                        uhe.printStackTrace();
                        System.exit(1);
                }

                try{
                        nifEnum = NetworkInterface.getNetworkInterfaces();
                        while (nifEnum.hasMoreElements()){
                                nif = nifEnum.nextElement();
                                try{
                                        System.out.println("nif is: " + nif);
                                        System.out.println("is sqeweb reachable? " +
                                                        sqeweb.isReachable(nif, 20, 10000));
                                }catch (IOException ioe){
                                        System.err.println("IOException caught !!");
                                        ioe.printStackTrace();
                                }
                        }
                }catch (SocketException se){
                        System.err.println("SocketException caught !!");
                        se.printStackTrace();
                }
        }
}

-----------------------END CODE--------------------------

-----------------------BEGIN OUTPUT----------------------
$ $JAVA_HOME/bin/java -showversion NIFBug
java version "1.5.0-beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-beta-b23)
Java HotSpot(TM) Client VM (build 1.5.0-beta-b23, mixed mode)

nif is: name:eth0 (eth0) index: 2 addresses:
/10.12.151.152;

is sqeweb reachable? true
nif is: name:lo (lo) index: 1 addresses:
/127.0.0.1;

IOException caught !!
java.net.ConnectException: Invalid argument
        at java.net.Inet4AddressImpl.isReachable0(Native Method)
        at java.net.Inet4AddressImpl.isReachable(Inet4AddressImpl.java:52)
        at java.net.InetAddress.isReachable(InetAddress.java:417)
        at NIFBug.main(NIFBug.java:24)
$

------------------------END OUTPUT-----------------------

-------------------BEGIN REDHAT 8.0 OUTPUT---------------
$ $JAVA_HOME/bin/java -showversion NIFBug
java version "1.5.0-beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-beta-b23)
Java HotSpot(TM) Client VM (build 1.5.0-beta-b23, mixed mode)

nif is: name:eth0 (eth0) index: 3 addresses:
/fe80:0:0:0:2d0:b7ff:fe4c:81e%3;
/10.12.151.153;

is sqeweb reachable? true
nif is: name:lo (lo) index: 1 addresses:
/0:0:0:0:0:0:0:1%1;
/127.0.0.1;

is sqeweb reachable? true
$
--------------------END REDHAT 8.0 OUTPUT----------------