Re: DNS based service discovery script

[David Fifield <david () bamsoftware com>]

On Tue, Sep 22, 2009 at 08:42:32PM +0530, Ravipriya Thushara wrote:
> I'm still learning Lua and haven't much idea on Nmap scripts yet. But
> I'll learn them soon and start script soon. By now I don't have access
> to a Mac OS  X machine. So i downloaded and installed Apple iTune on
> my windows machine. It have opened required ports and which can use
> for the script.

First you will want to make sure that you can scan port 5353 and find it
open. You will want to run a command like this:

nmap -F -sU <target>

(Replace "<target>" with the IP address of the host running DNS-SD.) You
are looking for output like this:

Not shown: 99 open|filtered ports
PORT     STATE SERVICE
5353/udp open  zeroconf

If you are using the 5.00 release, the port won't be "open" but
"open|filtered", perhaps like this:

All 100 scanned ports are open|filtered

But the important thing is that it is either "open" or "open|filtered".
Since this is your first script, I recommend first writing something
simple that just produces dummy output, like

PORT     STATE SERVICE
5353/udp open  zeroconf
|_ dns-sd: Hello, world!

You will want to read the book chapter on NSE at
http://nmap.org/book/nse.html, especially the tutorial at
http://nmap.org/book/nse-tutorial.html. Remember that to build the DNS
packets you should use the dns library, if possible.
http://nmap.org/nsedoc/lib/dns.html.

David Fifield

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