Re: DNS Amplification attack?

[Stuart Henderson <stu () spacehopper org>]

On 2009-01-21, Kameron Gasso <kgasso-lists () visp net> wrote:
> Christopher Morrow wrote:
> > a point to bear in mind here is that... 'its working' is good enough
> > for the bad folks :( no need to optimize when this works. Also, it's
> > likely this isn't all of the problem the spoofed requestors are seeing
> > these past few days :(
>
> Unfortunately, I can't restrict traffic to/from my authoritative
> nameservers like I can with my recursive ones, since it will break DNS
> resolution for outside visitors to domains we host.
>
> Fortunately, the spoofed queries are 60 bytes and my REFUSED responses
> are only 59, so it's a terribly inefficient way to DoS someone.
> However, I never said that the DDoS kiddies were smart - doesn't seem to
> be stopping them from trying. :(
>
> Thanks,

For you, yes.

In many cases, there's either no amplification or a small decrease
in traffic (though it makes it hard to shut off the true source).

In a few cases (e.g. tinydns), there's no response, so the attackers
traffic is wasted.

But what about the people that happen to have misconfigured their
authoritative DNS servers so that they're answering recursive queries
from the world? 60 -> 520 bytes isn't bad, and I bet it's not _that_
uncommon...