CODEWITHSUNDEEP
javaandroidc++network-programmingipv6
Jim
Jim

Reputation: 833

InetAddress.getByName fails getaddrinfo works

I've been having an issue with DNS lookup for IPv6 addresses that I can't seem to find good information about.

I'm trying to lookup an IPv6 address using InetAddress.getByName("ipv6.local.com"). It throws an UnknownHostException error.

The weird part is I know the DNS server can be contacted because this works:

InetAddress.getByName("ipv4.local.com")

I also know the IPv6 record is working because I can run:

nslookup ipv6.local.com

and it properly returns 3ffe:b00:0:1:4678:3eff:fe36:16e8.

Likewise, if I run the following in C++, I get a result with the above address as well:

int errorCode = getaddrinfo("ipv6.local.com", "4242", &hints, &res);

I have also tried Inet6Address.getByName(), but this also throws UnknownHostException. So why do getaddrinfo() and nslookup work and not InetAddress.getByName()?

I am attempting the DNS lookup from an Android device (Galaxy Tab S2 8") running Android 6.0.1 on the same network as the DNS server. The DNS server has a record "ipv4.local.com" pointing to 192.168.0.190, and a record "ipv6.local.com" pointing to 3ffe:b00:0:1:4678:3eff:fe36:16e8.

The DNS server is explicitly set in Wi-Fi settings on the Android device, and is running on 192.168.0.182.

Any ideas?

Upvotes: 1

Views: 1690

Answers (1)

Nijil
Nijil

Reputation: 356

I am not sure why IPv6 resolution is not working for you. Here is the example of Java code(java version "1.8.0_171") I tested:

package com.myjava.ip;


import java.net.InetAddress;
import java.net.UnknownHostException;

class MyIpByHost {

    public static void main(String a[]){

        try {
            InetAddress host = InetAddress.getByName("ipv6.google.com");
            System.out.println(host.getHostAddress());
        } catch (UnknownHostException ex) {
            ex.printStackTrace();
        }
    }
}

Output: java com/myjava/ip/MyIpByHost => 2404:6800:4003:c02:0:0:0:8a

This code returns IPv6 for endpoint "ipv6.google.com".

Java run C functions in it's backend to get work done. As you already know getaddrinfo() function of C supports IPv6, but gethostbyname() does not. You may be running outdated version of java with underlying C function gethostbyname() which does not support IPv6. I would suggest you to upgrade Java which will use getaddrinfo().

Upvotes: 3

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