[CentOS] DNS DoS attack

Jussi Hirvi
Fri, 17 Aug 2012 04:54:11 -0000

Looks like one of my name servers (CentOS 5) gets a lot of malicious
queries. The cpu load is constantly about 3 %. I put on stricter limits
on who is allowed recursive queries, but this does not affect the CPU
load. I also updated bind.

I temporarily turned on querylog (command: rndc querylog), and noticed
that I get over 200 queries like this per second:

> Aug 17 07:41:38 mx2 named[6873]: client 205.145.64.200#53: query (cache)
'ripe.net/ANY/IN' denied
> Aug 17 07:41:38 mx2 named[6873]: client 204.10.45.5#53: query (cache)
'ripe.net/ANY/IN' denied
> Aug 17 07:41:38 mx2 named[6873]: client 78.40.35.212#53: query (cache)
'ripe.net/ANY/IN' denied
> Aug 17 07:41:38 mx2 named[6873]: client 207.207.3.126#53: query (cache)
'ripe.net/ANY/IN' denied

Are there any ways to mitigate this, or do I just have to wait?

- Jussi