Re: [gentoo-user] How to prevent a dns amplification attack

[Pandu Poluan <pandu@poluan.info>]

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On Mar 28, 2013 10:38 PM, "Michael Mol" <mikemol@gmail.com> wrote:
>
> On 03/28/2013 04:51 AM, Norman Rieß wrote:
> > Hello,
> >
> > i am using pdns recursor to provide a dns server which should be usable
> > for everybody.The problem is, that the server seems to be used in dns
> > amplification attacks.
> > I googled around on how to prevent this but did not really find
> > something usefull.
> >
> > Does anyone got an idea about this?
>
> I'm not sure it can be done. You can't make a resolver available to
> "everybody" without somebody in that "everybody" group abusing it, and
> that's exacly what happens in a DNS amplification attack.
>
> Restrict your resolver to be accessible only to your network or, at
> most, those of the specific group of people you're seeking to help.
>
> You *might* try restricting the resolver to only respond to TCP requests
> rather than UDP requests, but if the resolver sends response data along
> with that first SYN+ACK, then nothing is solved, and you've opened
> yourself up to a SYN flood-based DoS attack. (OTOH, if your resolver
> went offline as a result of a SYN flood, at least it wouldn't be part of
> an amplification attack any longer...)
>

Can't we rate limit UDP DNS request?

E.g., limit each source IP to, let's say, 1 UDP per second?

That should be doable easily using iptables.

Rgds,
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