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Rational: Signing zones using DNSSEC authenticates the origin of the data and protects the data’s integrity. But for this to actually work, DNS resolvers performing recursive resolution must validate the data. This means they must be configured with a copy of the root Trust Anchor, and they must be told to validate signatures that are published alongside DNS records

Rationale: QNAME minimization (standardized in RFC 9156) is a technique to improve privacy for DNS queries. With QNAME minimization enabled, the DNS resolver doesn’t send the FQDN and query type (QTYPE) to resolvers it is querying to find the answer to a query, at the expense of a few additional queries.

Rationale: In the context of private networks, DoT or DoH must be enabled between the resolver on the local network(s) and an external, trusted DoT/DoH-enabled forwarding resolver. This ensures that DNS queries being forwarded from local clients are encrypted between the local resolver and the external forwarder. While DoT and DoH may reduce the visibility that local administrators have into the queries being forwarded by the local recursive resolver to an upstream DoT/DoH service, it will still be possible to monitor queries between clients and the local DNS resolver, either using passive DNS analysis or query logging.

Finally, DoT and DoH do not guarantee end-to-end privacy, only protection from third-party eavesdropping between hops that use DoT/DoH: the resolver that queries are being forwarded to should also use DoT/DoH when performing resolution.

Rationale: DNS software packages such as ISC BIND can be configured to function as authoritative and recursive resolution on the same installation. Historically, this was to avoid the cost and overhead of two separate servers, particularly before virtualization was common. This is still the default behavior in most Windows DNS deployments as well. Clients in Active Directory-enabled environments are typically configured to send recursive DNS lookups to DNS servers that by default serve a copy of the organization’s DNS zone. Queries for other domain names are resolved as usual (either directly, or by forwarding queries to an external server).

While this configuration does allow for a simpler setup (and faster lookup times) when looking up names within an organization’s own domain/zone, there are other problems with this configuration, including the risk for those DNS servers answering queries for “stale” domains that have since been delegated to other nameservers. This is a risk when the DNS servers are publicly reachable from the Internet.

Rationale: It is often necessary to enable logging of a service or application, including logging of data submitted by users and customers, in order to be able to troubleshoot problems and perform optimizations. Sometimes this is systematic and is enabled for forensic purposes (e.g., post mortem analysis of attacks, identifying misbehaving clients) or to be able to detect attacks as they are launched and before they can do major damage.

Either way, logging of data should be limited to the amount necessary ( in terms of both time and the depth of information being logged) to perform the tasks mentioned above, and should be disabled or reduced as soon as it is not required anymore. It is important to note here that legislation in many countries has made it mandatory to perform some level of logging of IP traffic, where providers and operators are asked to retain this data for months or even years. Operators should comply with these local data retention laws. DNS data can be leveraged to identify individual users, and great care must be taken that this data not be compromised, leaked, or otherwise accessed by unauthorized parties.

Rationale: To avoid outages where clients aren’t able to resolve names, it is best to always hand out at least two DNS resolvers when configuring clients, either using DHCP or any other provisioning method. Clients should be able to point to alternate resolver(s) to use in case of failure of the primary. Solutions using a load balancer in front of multiple servers usually aren’t practical because they introduce complexity, and stateful systems risk being overwhelmed by DoS/malware-related traffic from infected clients. An acceptable alternative to configuring a secondary resolver is to deploy Anycast so that multiple resolvers respond to queries sent to a unique resolver IP address.

Rationale: In the event of a vulnerability affecting a DNS software package, there is a risk that all of one’s DNS servers could become unavailable at the same time if they all run that same software.

Rationale: Monitoring of your DNS service is critical to ensure that it is available to users and customers. This can be achieved through local monitoring (hosted on premises) or a remote location, and either managed by yourself or a third party (outsourced/cloud based).