Odd InetAddress.isReachable() issue

Question 1

Thanks everyone, but I never did figure out or pinpoint why this oddity was happening. Everything I checked for was not the cause, so this question can be closed.

In any case, I ended up working around it completely. Instead of using InetAddress, I just went native and built my own ICMP ping class instead, via JNA, invoking Windows libraries IPHLPAPI.DLL and WSOCK32.DLL. Here is what I used...

public interface InetAddr extends StdCallLibrary {
    InetAddr INSTANCE = (InetAddr) 
            Native.loadLibrary("wsock32.dll", InetAddr.class);

    ULONG inet_addr(String cp);                     //in_addr creator. Creates the in_addr C struct used below
}

public interface IcmpEcho extends StdCallLibrary {
    IcmpEcho INSTANCE = (IcmpEcho)
            Native.loadLibrary("iphlpapi.dll", IcmpEcho.class);

    int IcmpSendEcho(
            HANDLE IcmpHandle,                      //Handle to the ICMP
            ULONG DestinationAddress,               //Destination address, in the form of an in_addr C Struct defaulted to ULONG
            Pointer RequestData,                    //Pointer to the buffer where my Message to be sent is
            short RequestSize,                      //size of the above buffer. sizeof(Message)
            byte[] RequestOptions,                  //OPTIONAL!! Can set this to NULL
            Pointer ReplyBuffer,                    //Pointer to the buffer where the replied echo is written to
            int ReplySize,                          //size of the above buffer. Normally its set to the sizeof(ICMP_ECHO_REPLY), but arbitrarily set it to 256 bytes
            int Timeout);                           //time, as int, for timeout

    HANDLE IcmpCreateFile();                        //win32 ICMP Handle creator

    boolean IcmpCloseHandle(HANDLE IcmpHandle);     //win32 ICMP Handle destroyer
}

And then using those to create the following method...

public void SendReply(String ipAddress) {
    final IcmpEcho icmpecho = IcmpEcho.INSTANCE;
    final InetAddr inetAddr = InetAddr.INSTANCE;
    HANDLE icmpHandle = icmpecho.IcmpCreateFile();
    byte[] message = new String("thisIsMyMessage!".toCharArray()).getBytes();
    Memory messageData = new Memory(32);                    //In C/C++ this would be: void *messageData = (void*) malloc(message.length);
    messageData.write(0, message, 0, message.length);       //but ignored the length and set it to 32 bytes instead for now
    Pointer requestData = messageData;
    Pointer replyBuffer = new Memory(256);
    replyBuffer.clear(256);

    // HERE IS THE NATIVE CALL!!
    reply = icmpecho.IcmpSendEcho(icmpHandle, 
            inetAddr.inet_addr(ipAddress), 
            requestData, 
            (short) 32, 
            null, 
            replyBuffer, 
            256, 
            timeout);
    // NATIVE CALL DONE, CHECK REPLY!!

    icmpecho.IcmpCloseHandle(icmpHandle);
}

public boolean IsReachable () {
    return (reply > 0);
}

Question 2

My guess is that your iteration logic to determine the different ip address is based upon different configuration hence your pc's fetches all addresses but your webserver doesn't.

Try adding debug in the logic where you build up the list of ip adresses to check.