A resolver is a program that resolves questions about names by sending those questions to appropriate servers and responding to the servers’ replies. In the most common application, a web browser uses a local stub resolver library on the same computer to look up names in the DNS. That stub resolver is part of the operating system. The stub resolver usually will forward queries to a caching resolver, a server or group of servers on the network dedicated to DNS services. Those resolvers will send queries to one or multiple authoritative servers in order to find the IP address for that DNS name.
Views - Split DNS
BIND 9 is unique in providing the ability to configure different views in a single BIND server. This allows you to give internal (on-network) and external (from the Internet) users different views of your DNS data, keeping some DNS information private.
Protect your clients from imposter sites by validating DNSSEC. In BIND 9, this is enabled with a single command. BIND 9 also has a Negative Trust Anchor feature, which temporarily disables DNSSEC validation when there is a problem with the authoritative server’s DNSSEC support. BIND 9 offers support for RFC 5011 maintenance of root key trust anchors.
Response Policy Zones - RPZ
A Response Policy Zone or RPZ is a specially constructed zone that specifies a policy rule set. The primary application is for blocking access to domains that are believed to be published for abusive or illegal purposes. There are companies that specialize in identifying abusive sites on the Internet, which market these lists in the form of RPZ feeds. For more information on RPZ, including a list of DNS reputation feed providers, see https://dnsrpz.info.
BIND supports QNAME minimization by default. This feature minimizes leakage of excessive detail about the query to systems that need those details. BIND does not yet support encryption natively (e.g. DNS over TLS), but this can be accomplished by deploying BIND with stunnel.