If you're reading this article (and indeed this magazine), you're probably not a huge fan of spam/malware/crapware/spyware, and so on. However, because you're also probably running Linux, you can avoid most of that, right? Just keep the system up to date, install AdBlock, apply SpamAssassin to your email, and so on – easy peasy lemon squeezy.

But, what happens if you have a device that doesn't support AdBlock or antivirus software (e.g., some of the more locked down Android devices)? Or, if you want to block certain domains or networks completely? Firewalling based on IP addresses is great, and you can even find country lists; however, that won't help you block attackers that quickly bounce their domain around multiple providers. If only there were a way to firewall stuff easily at the DNS level.

Response Policy Zones

Back in 2011, ISC, the company that produces BIND and DHCPD, decided this was a problem they wanted to address, so they rather cleverly added RPZ (Response Policy Zone) [1] support in a way that requires no changes to existing DNS client software or to other servers making use of the RPZ server. Basically, RPZ lets you define records to which that the response policy will be applied. These records can be the domain name being queried (QNAME), the IP address being returned in response to the query (IP), the name or domain of any DNS server used to fulfill a query (NSDNAME), and the IP address of any DNS server used to fulfill a query (NSIP).

[...]