On Thu, 22 May 2003, J. Matthew Miller, III wrote:
> Hi,
> I'm trying to work on some spam filtering software that uses dnsjava to
> do reverse DNS lookups using specific DNS servers. Specifically, i'm using
> DNS Realtime Blackhole Lists (DNSRBL's). Basically, the idea is that given
> a server, "permblock.easynet.net" -- and an ip address you want to check
> against that server's "known spammers list" (in this case, 69.1.80.67-- you
> do a lookup of "67.80.1.69.permblock.easynet.net."
>
> Some DNS servers this works with, others it doesnt. basically, any dns
> server i can't ping doesnt work. I get an "UnknownHostException" thrown
> when i create a resolver.
Is the reason you can't ping the server that it doesn't exist? You might
want to use dig (or dnsjava's lookup program) to determine if the servers
exist or not.
> Anyway, I'm wondering if there's a way around this that i'm not
> understanding, or if there's some limitation there, or if maybe i'm totally
> off base here.
If the server doesn't exist, there's no way you can send packets to it.
> Code is as follows:
>
> ----------------------------
>
> /*
> * TestDNS.java
> *
> * Created on May 22, 2003, 2:03 PM
> */
> import org.xbill.DNS.*;
> import java.net.*;
> import java.io.*;
> /**
> *
> * @author matt
> */
> public class TestDNS {
>
> /** Creates a new instance of TestDNS */
> public TestDNS() {
> }
> public static void main(String args[]) {
> try {
> String[] dnslist = new String[1];
> dnslist[0] = "permblock.easynet.net";
> Resolver resolver = null;
> try {
> resolver = new ExtendedResolver(dnslist);
> } catch (UnknownHostException ee) {
> ee.printStackTrace();
> }
> Name name = null;
> try {
> name = Name.fromString("67.80.1.69.permblock.easynet.net.");
> } catch (Exception e) {
> e.printStackTrace();
> }
> Record question = Record.newRecord(name, Type.A, DClass.IN);
> Message query = Message.newQuery(question);
> Message response = null;
> try {
> response = resolver.send(query);
> }
> catch (IOException e) {
> // A network error occurred. Press on.
> e.printStackTrace();
> System.exit(0);
> }
> short rcode = response.getHeader().getRcode();
> System.out.println("RCODE = " + rcode);
> } catch (Exception e) {
> e.printStackTrace();
> }
>
> }
>
> }
You'd be much better off using the Lookup class; something like:
String[] dnslist = new String[1];
dnslist[0] = "permblock.easynet.net";
Resolver resolver = null;
try {
resolver = new ExtendedResolver(dnslist);
} catch (UnknownHostException ee) {
ee.printStackTrace();
}
Lookup lookup = new Lookup("67.80.1.69.permblock.easynet.net.");
lookup.run();
if (lookup.getResult() == Lookup.SUCCESSFUL)
System.out.println("ok");
else
System.out.println("failed");
Brian
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