[dns-operations] dnsop-any-notimp violates the DNS standards

[Yunhong Gu]

On Mon, Mar 16, 2015 at 9:16 PM, Michael Sinatra <michael at brokendns.net>
wrote:

>
>
> On 03/16/15 18:07, Yunhong Gu wrote:
> >
> >
> > On Mon, Mar 16, 2015 at 8:50 PM, Michael Sinatra <michael at brokendns.net
> > <mailto:michael at brokendns.net>> wrote:
> >
> >     On 3/16/15 4:15 PM, P Vixie wrote:
> >     >
> >     >
> >     > On March 17, 2015 7:42:09 AM GMT+09:00, Michael Sinatra <
> michael at brokendns.net <mailto:michael at brokendns.net>> wrote:
> >     >>
> >     >>
> >     >> On 03/16/15 07:23, bert hubert wrote:
> >     >>
> >     >>> Separately, I fail to see why we actually need to outlaw ANY
> queries
> >     >> when we
> >     >>> can happily TC=1 them.
> >     >>
> >     >> If the public recursives also support TC=1 on all ANY queries,
> then
> >     >> this
> >     >> works.  If not, the issue arises where just-below-the-radar
> attacks are
> >     >> using many public recursives, in which case you're not stopping
> much.
> >     >
> >     > Michael, what attacks do you think we can stop by limiting ANY?
> Paul
> >
> >     The attack that I have had to grapple with is this:
> >
> >     * Someone sets up a bot to query public recursives (google, opendns,
> >     level3, etc.) for a particular domain whose ANY response is large.
> >     (This _usually_ means DNSSEC-signed.)
> >
> >     * The query from each <client,domain,qtype> tuple is just barely slow
> >     enough not to trigger rate limiting from the public recursive
> service.
> >
> >     * The backend of the public recursive service queries my
> authoritatives
> >     for some of the involved domains.  Suppose the response is just under
> >     the usual typical default EDNS0 buffer size of 4096.
> >
> >     * These domains are DNSSEC-signed with NSEC3.  Many tools set the
> TTL of
> >     NSEC3PARAM to 0 when signing zones with NSEC3.  The NSEC3PARAM RR is
> >     part of the ANY response.
> >
> >
> > Sounds to me this is the root cause of the problem and ANY is the just a
> > scapegoat.
>
> Giving NSEC3PARAM a positive TTL would prevent my headache, but it
> wouldn't help the victim of the attack, and would probably make it worse
> for the victim.
>

The reason that this response can be used for an amplification attack is
its size, not the ANY type. A responses with 200 A records can be used for
the same purpose. The (even deeper) root cause is the use of UDP in DNS
protocol. I just do not think banning ANY touches any of these fundamental
issues.



>
> michael
>
>
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