How can I tell in the log if a query was successful or refused due to recursion?
Mark Andrews
Mark_Andrews at isc.org
Thu Dec 15 03:12:12 UTC 2005
> 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
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