From 18 March on the Internet experienced one of the most massive distributed denial of service (DDoS) attacks in its history. In the post-incident analysis it became quickly clear the attackers exploited a specific flaw in how many DNS servers are configured. Too many DNS servers are configured as open resolvers returning information to anyone who asks.
BELTUG urges all organisations, companies and ISPs running DNS servers to check and if necessary correct the configuration of the open DNS resolvers to prevent them from being used as an attack vector in a DDoS attack.
Guidelines concerning the configuration of your DNS servers can be found on the Open DNS Resolver Project website. DNS servers should be configured according to the guidelines offered in RFC 5358 / BCP 140.
Read the BELTUG recommendations.