Maintained by: NLnet Labs

[Unbound-users] Unbound not resolving after attack

Dominick Rivard
Wed Mar 13 19:52:25 CET 2013



I am trying to find the cause of an issue we have been experiencing last
Thursday. We are running multiple Unbound servers 

In order to provide internet to our users. I would say we were under attack
with a couple of IPs trying to request as many as possible records for “ANY?”. The DNS were resolving until a certain period of time where it
became just impossible to resolve anything. My first try was to restart the
unbound service and it worked for a couple of second, then it failed again.
Next step was to block these IPs with iptables, but still it wasn’t
resolving, even after a second restart of the unbound service. 


What resolved the issue was to route the trafic to a different NAT ip so the
unbound servers were seen as a different public ip when going to internet.
At that point I thought I could have been throttled or blacklisted by the
roots servers.  I wrote to them and they explain to me that they don’t have
such a mean to  limite the rate of queries or throttle any of our request. 


So I am turning to you guys to ask some question what could be slowing me
down or blocking me from my local unbound server to resolve any name? Is
there any configuration I  need to change? 


How would you prevent these kind of attack in the future?


Unbound version: 1.4.18

OS: Debian Squeeze 6.0.6


Best regards.

Dominick Rivard,
Solutions Architect


5275 Queen Mary 
Montréal, Qc
H3W 1Y3
Tel: 514-385-4448 ext 126
Fax: 514-385-6660

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