bugtraq - Re: DNS query spam

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Message-ID: <200511300441.jAU4fbcX023282@lo.tech.org>
Date: Wed, 30 Nov 2005 04:41:37 +0000
From: Stephen Stuart <stuart@...h.org>
To: Antone Roundy <antone@...kotribe.com>
Cc: bugtraq@...urityfocus.com
Subject: Re: DNS query spam


> Assuming you use Bind, can edit your named.conf file, only wish to  
> provide recursive DNS services (ie. handle queries for domains that  
> you are not authoritative for) to a known range of IP addresses, and  
> the query is for a domain that you're not authoritative for, you can  
> solve the problem by adding something like this to named.conf:
> 
> options {
>     allow-recursion { 127.0.0.1/32; };
> };
> 
> That particular setting would cause Bind to ignore recursive queries  
> from all IP addresses except 127.0.0.1 (localhost).  My DNS server  
> only provides recursive queries for itself, so the setting was easy  
> for me.  After I started blocking recursive queries, it took a week  
> or so for the bogus traffic to stop.  But in the mean time, since I  
> wasn't sending responses, the amount of my bandwidth that was wasted  
> decreased dramatically.

Small correction: that will cause BIND to not perform recursive
queries from any IP address except 127.0.0.1. You will still answer
queries from cache for all comers, unless you also restrict queries in
general to 127.0.0.1/32:

options {
    allow-query { 127.0.0.1/32; };
};

Stephen