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

[Kevin Darcy]

Mark Andrews wrote:

>>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.
>  
>
OK, I get the whole "forge the address of the victim" mechanic now, but 
I'm still missing something here. A typical response to an arbitrary 
*non*-recursive query, is an "upwards referral" to the root zone, about 
440-450 bytes. A typical response to e.tn.co.za/ANY with recursion being 
honored is less than 90 bytes. So why would the perpetrator choose to 
make their queries recursive?

                                                                         
                                    - Kevin