How can I tell in the log if a query was successful or refused due to recursion?

[Mark Andrews]

> Tony Toews wrote:
> 
> >Folks
> >
> >I'm told that my DNS server is participating in "recursive dns dos 
> >attack".  
> >
> >So I've locked things down I think.  More on that to follow as a 
> >separate posting.   So I'm looking at my log entries and I'm seeing the 
> >same kind of traffic now as before I removed the recursion option.
> >
> >How can I tell in the log if a query was successful or refused due to 
> >recursion?  An example of my current log follows:
> >
> >14-Dec-2005 18:37:24.145 client 216.18.224.133#41538: query: e.tn.co.za ANY 
> >ANY +E
> >14-Dec-2005 18:37:25.599 client 216.18.224.133#51561: query: e.tn.co.za ANY 
> >ANY +E
> >14-Dec-2005 18:37:26.067 client 216.18.224.133#46417: query: e.tn.co.za ANY 
> >ANY +E
> >14-Dec-2005 18:37:27.630 client 216.18.224.133#43677: query: e.tn.co.za ANY 
> >ANY +E
> >14-Dec-2005 18:37:28.114 client 216.18.224.133#58498: query: e.tn.co.za ANY 
> >ANY +E
> >
> >Bind 9.3.1 on a Win 2003 Server.  Serving as DNS for 23 very low traffic 
> >domains hosted on that same system.
> >  
> >
> There's no way I know of to tell via normal BIND 9 logging whether a 
> query was "successful" or not. For that matter, it depends on what you 
> mean by "success". Is a NODATA response (NOERROR with "no relevant 
> answers" in the Answer Section) "success"? How about a referral?
> 
> You could, I suppose, configure some addresses locally on virtual 
> interfaces (or whatever the Win 2003 equivalent would be), and send some 
> queries from those source addresses, using dig's -b option, or something 
> similar, just to see how the responses come back.
> 
> By the way, if those queries above are supposed to be some sort of 
> "recursive DNS DoS attack", then it's a pretty lame one: since BIND 
> treats ANY queries as non-recursive whenever anything owned by the name 
> exists in cache, the attack could be easily fooled, without touching any 
> "production" data, by putting some bogus RRset out there (e.g. TXT, RP) 
> with a really long TTL. As it is, since e.tn.co.za doesn't exist and the 
> relevant negative-caching TTL is 1 day, I can't imagine the negative 
> impact being very high (but I'm open to the possibility that the owner 
> of the zone may have deleted that name subsequent to the beginning of 
> the attack...)
> 
> - Kevin

	It's a recursive DNS DDoS amplification attack.  The client's
	address is forged.  It is depending on named to amplify the
	traffic.  The actual target is 216.18.224.133.

	Mind you "e.tn.co.za/IN/TXT" would be just as effective as
	"e.tn.co.za/ANY/ANY" and would not stick out like a sore
	thumb.

	Mark
--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org