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Can some explain Context.list() in DNS terms?

 
 
robert
Guest
Posts: n/a
 
      12-16-2006
Hi all,

First question: using nmap 10.101.40.200 shows port 53 and dns running
so why would DirContext.list() throw "OperationNotSupportedException:
DNS service refused" ? The goal: Find all hosts that are known to a
nameserver. If one of the hosts is a NS record, search that server as
well. I can switch - as the commented out code shows - to use the
public dns server via calculateDNS("bee.uspnet.usp.br", "usp.br") and
the code works fine. Why I can't connect to 10.101.40.200 completely
baffles me - what exactly is DirContext.list() trying to look for in
the DNS service ? I tried DNSJava as well with the same problem.

Second question: Can someone explain the equivalent DIG or NSLOOKUP
commands that and the subsequent:

NamingEnumeration hostEnumeration = DirContext.list()
String host = ((NameClassPair) hostEnumeration.next())
.getNameInNamespace();

I want to post the DNS parts of the question to the approriate
newsgroup, but I'm having a hard time using DIG and NSLOOKUP to repeat
the results.

Here's my code - there are a few sockets open, already cancelled,
waiting to timeout which is ok. Not sure about the recursion part -
still thinking about it.

package org;

import java.util.concurrent.*;

public class RecursionLatch {
private final CountDownLatch done = new CountDownLatch(1);

public boolean isSet() {
return (done.getCount() == 0);
}

public synchronized void setCompleted() {
if (!isSet()) {
done.countDown();
}
}

public void taskCompleted() throws InterruptedException {
done.await();
}
}

package org;

import static java.lang.System.out;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Hashtable;
import java.util.List;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.Callable;
import java.util.concurrent.Future;
import java.util.concurrent.atomic.AtomicInteger;

import javax.naming.NameClassPair;
import javax.naming.NamingEnumeration;
import javax.naming.directory.Attributes;
import javax.naming.directory.DirContext;
import javax.naming.directory.InitialDirContext;
import javax.naming.directory.Attribute;
import javax.naming.directory.Attributes;
import javax.naming.NamingException;

public class DNS
{
private static final AtomicInteger taskCount = new AtomicInteger(0);
private static final RecursionLatch solution = new RecursionLatch();

public static void main(String[] args) throws Exception {
helloDNS();
}

/************************************************** *****************
Use this method to test dns
************************************************** *****************/
private static void helloDNS() throws Exception {
//calculateDNS("10.101.40.200", "atlantico.com.br");
calculateDNS("bee.uspnet.usp.br", "usp.br");
out.println("calculateDNS returned, waiting for cancelled
sockets to timeout...");
}

private static List<String> calculateDNS(final String ipDNS, final
String domain)
throws Exception {

final Hashtable<String, String> env = new Hashtable<String,
String>();
env.put("java.naming.factory.initial",
"com.sun.jndi.dns.DnsContextFactory");
env.put("java.naming.provider.url", "dns://" + ipDNS + "/");

final DirContext ictx;
ictx = new InitialDirContext(env);
ExecutorService exec = Executors.newCachedThreadPool();

NamingEnumeration hostEnumeration = null;
boolean gotList = false;
Callable <NamingEnumeration> listTask =
new Callable<NamingEnumeration>() {
public NamingEnumeration call() {
try {
return ictx.list(domain);
} catch (Exception ex) {
ex.printStackTrace();
}
return null;
}
};
Future <NamingEnumeration> future = exec.submit(listTask);
try {
hostEnumeration = future.get(10L, TimeUnit.SECONDS);
if (hostEnumeration != null) {
gotList = true;
}
} catch (Exception ex) {
ex.printStackTrace();
} finally {
future.cancel(true);
}

try {
if (!gotList) {
throw new Exception("Can't connect to DNS server");
}
// skip those already found
Queue <String> domainsVisitedQueue = new
ConcurrentLinkedQueue<String>();
domainsVisitedQueue.add(domain);

Queue <String> resultQueue = new
ConcurrentLinkedQueue<String>();
parallelRecursiveDNS(exec, ictx, hostEnumeration,
domainsVisitedQueue, resultQueue );
// wait for latch
solution.taskCompleted();
out.println("latch returned, waiting for shutdown");

for (String s : resultQueue) {
out.println("WTF: " + s);
}
return new ArrayList<String>(resultQueue);
} catch (Exception ex) {
ex.printStackTrace();
throw new Exception (ex);
} finally {
out.println("shutting down DirContext");
long ictxStart = System.currentTimeMillis();
if (ictx != null) {
try {
ictx.close();
} catch (NamingException ex) {
ex.printStackTrace();
}
}
long ictxEnd = System.currentTimeMillis();
out.println("runnable execution time was "
+ (ictxStart - ictxStart) / 1000 + " seconds ");
// may have some sockets still open that have been cancelled
- that's ok
exec.shutdownNow();
out.println("termination complete");
}

}

private static void parallelRecursiveDNS(final ExecutorService exec,
final DirContext ictx,
final NamingEnumeration hostEnumeration, final
Collection<String> domainsVisitedQueue,
final Collection<String> results)
throws Exception {


while (hostEnumeration.hasMore()) {

taskCount.incrementAndGet();
exec.execute(new Runnable() {
public void run() {
long runStart = System.currentTimeMillis();
try {
String host = null;
host = ((NameClassPair) hostEnumeration.next())
.getNameInNamespace();
if (results.contains(host)) {
return;
}
results.add(host);
out.println("Found host: " + host);
Attributes aDNS = ictx.getAttributes(host,
new String[] { "NS" });
NamingEnumeration allDNS = aDNS.getAll();
while (allDNS.hasMore()) {
out.println("Entering allDNS: ");
Attribute attr = (Attribute) allDNS.next();
NamingEnumeration values = attr.getAll();
final String dns = values.next().toString();
if (domainsVisitedQueue.contains(dns)) {
continue;
}
domainsVisitedQueue.add(dns);

NamingEnumeration newEnumeration = null;
boolean gotList = false;
Callable <NamingEnumeration> listTask =
new Callable<NamingEnumeration>() {
public NamingEnumeration call() {
try {
out.println("doing future on
ictx.list()");
return ictx.list(dns);
} catch (Exception ex) {
ex.printStackTrace();
}
return null;
}
};
Future <NamingEnumeration> future =
exec.submit(listTask);
try {
newEnumeration = future.get(10L,
TimeUnit.SECONDS);
if (newEnumeration != null) {
gotList = true;
}
} catch (Exception ex) {
ex.printStackTrace();
} finally {
future.cancel(true);
}
if (!gotList) {
continue;
}
parallelRecursiveDNS(exec, ictx,
newEnumeration, domainsVisitedQueue, results);
}
} catch (Exception ex) {
ex.printStackTrace();
} finally {
long runEnd = System.currentTimeMillis();
out.println("runnable execution time was "
+ (runEnd - runStart) / 1000 + " seconds ");
if (taskCount.decrementAndGet() == 0) {
out.println("\n\nparallelRecursiveDNS
finished\n\n");
solution.setCompleted();
}
}

}
});
}
}
}

 
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Martin Gregorie
Guest
Posts: n/a
 
      12-16-2006
robert wrote:
> Hi all,
>
> First question: using nmap 10.101.40.200 shows port 53 and dns running
> so why would DirContext.list() throw "OperationNotSupportedException:
> DNS service refused" ?
>

Sounds to me as though either the DNS at 10.101.40.200 is disallowing
queries from your host or its disallowing your attempt to to download
the entire zone content. Talking to its sysadmin mat be a good idea.

> Second question: Can someone explain the equivalent DIG or NSLOOKUP
> commands that and the subsequent:
>

dig -t AXFR @192.168.7.2 gregorie.org

will do a zone transfer from my DNS (192.168.7.2), which is what you
appear the be trying to do.

dig -t ANY @192.168.7.2 cretin.gregorie.org

will get all records for the named host (this laptop) and the A record
for the DNS server.

dig -t A @192.168.7.2 cretin.gregorie.org

just gets the A records for the named host and the DNS server.
Hopefully, this will get you going. If all else fails, why not fire up
ethereal / wireshark and take a look at the network traffic your DNS
query is generating?



--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |
 
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robert
Guest
Posts: n/a
 
      12-18-2006

Martin Gregorie escreveu:

> robert wrote:
> > Hi all,
> >
> > First question: using nmap 10.101.40.200 shows port 53 and dns running
> > so why would DirContext.list() throw "OperationNotSupportedException:
> > DNS service refused" ?
> >

> Sounds to me as though either the DNS at 10.101.40.200 is disallowing
> queries from your host or its disallowing your attempt to to download
> the entire zone content. Talking to its sysadmin mat be a good idea.
>
> > Second question: Can someone explain the equivalent DIG or NSLOOKUP
> > commands that and the subsequent:
> >

> dig -t AXFR @192.168.7.2 gregorie.org
>
> will do a zone transfer from my DNS (192.168.7.2), which is what you
> appear the be trying to do.
>
> dig -t ANY @192.168.7.2 cretin.gregorie.org
>
> will get all records for the named host (this laptop) and the A record
> for the DNS server.
>
> dig -t A @192.168.7.2 cretin.gregorie.org
>
> just gets the A records for the named host and the DNS server.
> Hopefully, this will get you going. If all else fails, why not fire up
> ethereal / wireshark and take a look at the network traffic your DNS
> query is generating?
>


Martin, thanks alot for your helpful reply but I'm still stuck, as
these commands are not doing what the program is doing. The one public
dns server that is working for me is the university of são paulo,
usp.br . Maybe I just misunderstand. Here's some commands I ran:

dig usp.br
....
usp.br. 10800 IN SOA bee.uspnet.usp.br

dig -t AXFR @bee.uspnet.usp.br usp.br
....
Transfer failed

This command gives me about 5 entries:
dig -t ANY @bee.uspnet.usp.br usp.br

bee.uspnet.usp.br.
usp.br. 86400 IN NS ns1.ansp.br.
usp.br. 86400 IN NS reno.uspnet.usp.br.
usp.br. 86400 IN NS bee08.uspnet.usp.br.
usp.br. 86400 IN TXT "v=spf1
ip4:143.107.0.0/16 ~all"
usp.br. 1200 IN MX 0 kavir.uspnet.usp.br.
usp.br. 1200 IN MX 10 sinai.uspnet.usp.br.

However, my program gives about 40 entries before going into recursion:

[java] Found host: proteos.usp.br.
[java] Found host: esalq.usp.br.
[java] Found host: nupegel.usp.br.
[java] Found host: bibliotecas-cruesp.usp.br.
[java] Found host: linorg.usp.br.
[java] Found host: neuroimago.usp.br.
[java] Found host: semfio.usp.br.
[java] Found host: diploma.usp.br.
[java] Found host: fflch.usp.br.
[java] Found host: forp.usp.br.
...

I'll have to wait for off hours to run ethereal . If anyone want to run
this code, I created a zip that just needs ant and java 5.0 . Just
unzip, 'cd dns' and 'ant dns' .

http://www.braziloutsource.com/random/dns.zip

Thanks!
Robert

 
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Martin Gregorie
Guest
Posts: n/a
 
      12-18-2006
robert wrote:
> Martin, thanks alot for your helpful reply but I'm still stuck, as
> these commands are not doing what the program is doing.
>

Its essential to use @dnshost in the dig command because that makes sure
that dig will interrogate the DNS you want. Otherwise it will just send
the command to whichever DNS your /etc/resolv.conf selects.

> dig -t AXFR @bee.uspnet.usp.br usp.br
> ...
> Transfer failed
>

That doesn't surprise me because a public DNS probably won't let just
anybody request a zone transfer

> However, my program gives about 40 entries before going into recursion:
>

Obviously dig isn't using the same DNS command set that your program
uses. To find out more you'll have to do one of the following:

- find the source for dig and DirContext and friends and compare to
commands they issue. I can't be more specific because I'm still on JDK
1.4 and can't see the methods you're using.

- use Wireshark, preferably on a workstation that isn't doing anything
else, to record and compare the command sets that dig and your program
are issuing. Simply running "tshark >capturefile.txt will capture
everything sent and received on the machine's first Ethernet connection.
You have to be root to run it: it usually lives in /sbin or /usr/sbin.

> If anyone want to run
> this code, I created a zip that just needs ant and java 5.0 . Just
> unzip, 'cd dns' and 'ant dns' .
>
> http://www.braziloutsource.com/random/dns.zip
>

I don't have ant or Java 5 installed, so I'll pass on that.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |
 
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