full-disclosure - Re: recursive DNS servers DDoS as a growing DDoSproblem

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Date: Wed Mar  8 18:50:14 2006
From: securitylists at uniontown.com (Security Lists)
Subject: Re: recursive DNS servers DDoS as a growing
	DDoSproblem

Sorry, I don't see this as amplification in your example, because YOUR 
dns servers are 100% of the traffic.  1:1 ratio.

Now, if you get the world to cache your text records, and have THEM 
flood with source-spoofed UDP (unrelated to the victim's DNS servers), 
that'd work, and is actually a good example of amplification.  There's 
plenty of open DNS servers out there that'll do this, but each one of 
them is going to hit your local dns server initially.

-Mark Coleman


Geo. wrote:
>>> In the scenario you describe, I cannot see any actual amplification...
>>>       
>
> I'll give you a senario where you can see.
>
> lets say you have 2 name servers that are local to you.
>
> I setup a domain, example.com. In this domain I create a text record which is 100K in length, I don't know, perhaps I paste the source code to decss in it, whatever it's a big text record.
>
> Now I simply spoof a UDP packet using your IP address as the source address and send it to both of your dns servers. This packet is a query for the example.com text record. I have now sent two very small packets and you have received 200K of traffic. That's the amplification, one small udp packet, one large text record in return.
>
> Note, I don't have to use your local servers, but this way it makes it more fun to troubleshoot because it looks like you are the cause of your own flooding..
>
> Geo.
>
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