Java .netAddress.getAllByName() 不返回 Windows 上的 IPv6 地址，即使 -Djava.net.preferIPv6Addresses=true

Question

My DNS contains two records for ServerA:

• an A record with its IPv4 address: 10.25.46.130
• an AAAA record with its IPv6 address: fda8:6c3:ce53:a890::55

I am not able to get my SimpleClient.java program (source at the end of this post) on a Windows server to list the IPv6 address of ServerA using .netAddress.getAllByName() , even when configuring the JVM with -Djava.net.preferIPv6Addresses=true .

The same test running on an IPv6 enabled Linux server is successful.

Configuration details:

• Windows: Server 2019 Standard (10.0.17763)
• Java: OpenJDK 11.0.5+

The output of ipconfig on the Windows server shows that IPv6 seems enabled:

> ipconfig
Windows IP Configuration

Ethernet adapter Ethernet:

   Connection-specific DNS Suffix  . :
   IPv4 Address. . . . . . . . . . . : 10.25.0.214
   Subnet Mask . . . . . . . . . . . : X.X.X.X
   Default Gateway . . . . . . . . . : X.X.X.X

Ethernet adapter Ethernet 2:

   Connection-specific DNS Suffix  . : fr.company.com
   IPv6 Address. . . . . . . . . . . : fda8:6c3:ce53:a890::3
   Link-local IPv6 Address . . . . . : X.X.X.X::X
   Default Gateway . . . . . . . . . : X.X.X.X::X

The nslookup output from the Windows server is the expected one:

> nslookup ServerA
Server:  dns.fr.company.com
Address:  X.X.X.X

Non-authoritative answer:
Name:    ServerA.fr.company.com
Addresses:  fda8:6c3:ce53:a890::55
          10.25.46.130

I am able to successfully run ping -6 ServerA from the Windows server:

> ping -6 ServerA
Pinging ServerA.fr.company.com [fda8:6c3:ce53:a890::55] with 32 bytes of data:
Reply from fda8:6c3:ce53:a890::55: time<1ms
Reply from fda8:6c3:ce53:a890::55: time<1ms

Below is the expected output running from an IPv6 enabled Linux server:

# IPv4 (default)
$ java SimpleClient.java ServerA 12345
preferIPv6Addresses: null
InetAddress.getByName()
ServerA/10.25.46.130
InetAddress.getAllByName()
ServerA/10.25.46.130
ServerA/fda8:6c3:ce53:a890:0:0:0:55

# IPv6
$ java -Djava.net.preferIPv6Addresses=true SimpleClient.java ServerA 12345
preferIPv6Addresses: true
InetAddress.getByName()
ServerA/fda8:6c3:ce53:a890:0:0:0:55
InetAddress.getAllByName()
ServerA/fda8:6c3:ce53:a890:0:0:0:55
ServerA/10.25.46.130

The same test failing on the Windows server:

# IPv4 (default)
> java SimpleClient.java ServerA 12345
preferIPv6Addresses: null
InetAddress.getByName()
ServerA/10.25.46.130
InetAddress.getAllByName()
ServerA/10.25.46.130

# IPv6
> java -Djava.net.preferIPv6Addresses=true SimpleClient.java ServerA 12345
preferIPv6Addresses: true
InetAddress.getByName()
ServerA/10.25.46.130
InetAddress.getAllByName()
ServerA/10.25.46.130

On the Windows server, the call to .netAddress.getAllByName() is only returning a single IPv4 address and not both an IPv4 and IPv6 address like as expected on the Linux IPv6 enabled server.

I can reproduce the same behavior on a Linux server with IPv6 disabled (grub and kernel settings):

# IPv4 (default)
$ java SimpleClient.java ServerA 12345
preferIPv6Addresses: null
InetAddress.getByName()
ServerA/10.25.46.130
InetAddress.getAllByName()
ServerA/10.25.46.130

# IPv6
$ java -Djava.net.preferIPv6Addresses=true SimpleClient.java ServerA 12345
preferIPv6Addresses: true
InetAddress.getByName()
ServerA/10.25.46.130
InetAddress.getAllByName()
ServerA/10.25.46.130

From these tests, I conclude that something is wrong somewhere on the IPv6 configuration of the Windows server but I don't know what.

Some notes and stuff I tried:

• Manually adding the IPv6 address of ServerA in C:\Windows\System32\drivers\etc\hosts results in the program to list the IPv6 address, but only this one.
• I did not find a DisabledComponents key in the registy for the path Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters

Below is the code for SampleClient.java :

import java.net.Socket;
import java.net.UnknownHostException;
import java.net.InetAddress;
import java.io.InputStreamReader;
import java.io.InputStream;
import java.io.BufferedReader;
import java.io.IOException;

public class SimpleClient {
    public static void main(String[] args) {
        if (args.length < 2) return;
        String hostname = args[0];
        System.out.println("preferIPv6Addresses: " + System.getProperty("java.net.preferIPv6Addresses"));
        try {
          System.out.println("InetAddress.getByName()");
          System.out.println(InetAddress.getByName(hostname));
          InetAddress[] addresses = InetAddress.getAllByName(hostname);
          System.out.println("InetAddress.getAllByName()");
          for (InetAddress address : addresses) {
            System.out.println(address);
          }
        } catch (UnknownHostException ex) {
            System.out.println("Server not found: " + ex.getMessage());
        }
        int port = Integer.parseInt(args[1]);
        try (Socket socket = new Socket(hostname, port)) {
            InputStream input = socket.getInputStream();
            BufferedReader reader = new BufferedReader(new InputStreamReader(input));
            System.out.println(reader.readLine());
        } catch (UnknownHostException ex) {
            System.out.println("Server not found: " + ex.getMessage());
        } catch (IOException ex) {
            System.out.println("I/O error: " + ex.getMessage());
        }
    }
}

Can somebody hint at something that might be wrong on the Windows server configuration?

Thank you.

Answer 1

The issue was in the.network configuration of the Windows server.

The server was provisioned with two.network interfaces to segregate between IPv4 and IPv6, each interface being configured to support a single.network stack.

Keeping a single.network interface and configuring both IPv4 and IPv6 on this interface fixed the issue.

More details on the SuperUser question: https://superuser.com/questions/1719174/jvm-on-windows-not-returning-any-ipv6-address-in-dns-lookup