Dear colleagues, Yesterday, Monday 14 December 2015, RIPE NCC Authoritative DNS services were functioning in a severely degraded state during parts of the day. This was due to an attack on one of the ccTLDs for which the NCC hosts a secondary DNS service. The attack traffic started around 08:00 UTC. RIPE NCC staff applied various countermeasures during the day. These mitigations were effective for some time. However, after implementing each of these mitigations, the traffic patterns were modified to evade them. Towards the end of the day, the volume of the attack traffic targeted at our servers had increased to such a level that it was overloading our incoming links and our mitigation measures were no longer sufficiently effective. At that time we were forced to contact our upstream peers to assist us with mitigation measures. Apart from the ccTLD service for the attacked domain, normal services were restored at around 18:30 UTC. The attack is ongoing, and we continue with mitigation measures in order to provide the best service possible under the circumstances. We note that attacks like this rely on spoofing source addresses in the attack packets. Therefore, Source Address Validation and BCP-38 should be used wherever possible to reduce the ability to abuse networks to transmit spoofed source packets. Kind regards, Romeo Zwart