What is RPZ?

A Response Policy Zone (RPZ) is a powerful feature embedded within the Domain Name System (DNS), allowing administrators to wield granular control over DNS resolution processes. Essentially, RPZ enables administrators to control how DNS queries are resolved based on predefined policies. These policies can be used to block access to certain domains or redirect users to alternative locations based on various criteria such as domain name, IP address, or other attributes. RPZ is often used for implementing security measures such as blocking access to malicious or inappropriate websites, and for ensuring compliance.

Response Policy Zones (RPZs) allow administrators to control what their users can and cannot look up using a recursive DNS server. By analyzing the reputation of the servers and services, administrators can decide on actions to take when certain domain names are queried or when DNS responses point to malicious servers.

RPZs enable the creation of policies to manage specific queries and responses. Possible actions include redirecting clients to an internal security page and storing these policies in authoritative zones on DNS servers. RPZ zones can be shared between DNS servers through zone transfers.

RPZ data can be sourced from a threat intelligence provider, where they act as the primary zone, or created in-house, termed “Local RPZs.” Local RPZs typically include allow list (whitelist) and deny list (blacklist) items deemed critical by the organization for zero trust frameworks, ensuring that no external RPZ can override these local policies.

Understanding reputation is key to creating effective RPZs. Reputation refers to a zone’s history of malicious activity, tracked by Threat Intelligence service providers who predict and analyze malicious behavior. These providers publish reputation data for broader use. RPZs make policy data available in DNS zones, which is then transferred between servers using standard DNS protocols.

RPZ Key Terminologies

Resource Records

Resource records within an RPZ express DNS policies applied to domain names (QNAME) or target data (RDATA). The owner name of an RPZ QNAME policy resource record set (RRSET) corresponds to the domain triggering the filter. For instance, if the policy zone is rpz.efficientip.com, the policy affecting dangerous.visit.nastysite.net would attach to dangerous.visit.nastysite.net.rpz.efficientip.com. A wildcard such as *.nastysite.net.rpz.efficientip.com would cover all subdomains under nastysite.net.

Triggers

Triggers determine whether a query or response matches a specific entry in an RPZ.

• QNAME Trigger: Operates on the query’s NAME field. Wildcards can block a site and its subdomains, e.g. *.nastysite.com.
• IP Trigger: Matches the IPv4 or IPv6 address in the response’s RDATA field. Useful for blocking known malicious IPs regardless of the domain name.
• Client IP Trigger: Matches the source IP address of the client initiating a query, effective for targeting compromised hosts.
• NSDNAME Trigger: Matches the name of the authoritative name server found during recursion, targeting all domains served by a malicious name server.
• NSIP Trigger: Matches the IP addresses in A and AAAA records of name servers, blocking all domains served by these name servers.

RPZ Responses

When a trigger matches a record in an RPZ, one of the following actions can be taken:

• NXDOMAIN: Returns NXDOMAIN, indicating the domain does not exist.
• NODATA: Returns NODATA, indicating no data of the requested type exists for the domain.
• NO-OP/PASSTHRU: Allows the query to pass through without modification but logs the event.
• Local Data: Returns data matching the query type if available, otherwise returns NODATA.

DNS Server

A DNS server is a specialized computer program or server responsible for storing DNS records and responding to DNS queries from clients. These servers play a pivotal role in facilitating DNS resolution by efficiently translating domain names into IP addresses. DNS servers are the linchpins of the DNS ecosystem, ensuring the seamless operation of internet communication protocols.

DNS Query

A DNS query is a request initiated by a client, typically a user’s device or application, sent to a DNS server. These queries seek to obtain the IP address associated with a specific domain name, enabling the client to establish connections with desired internet resources. DNS queries are the initial triggers that set in motion the DNS resolution process.

DNS Resolution

DNS resolution is the fundamental process by which domain names, such as “example.com,” are translated into their corresponding IP addresses, such as “192.0.2.1.” This translation is vital for enabling computers to locate and communicate with internet resources seamlessly. DNS resolution forms the backbone of internet functionality, facilitating the seamless exchange of data across global networks.

Zone File

A zone file is a structured text file containing DNS resource records pertinent to a specific DNS zone. These records encompass essential information such as domain names, corresponding IP addresses, and other pertinent DNS settings. In the realm of RPZ, zone files serve as repositories for defining policy rules that govern DNS resolution behaviors within designated zones.

Zone Transfer

Zone transfer denotes the process of replicating DNS zone data from one DNS server to another. In the context of RPZ, zone transfers play a pivotal role in disseminating RPZ policy data across authoritative DNS servers, ensuring uniform enforcement of policy directives across network infrastructures.

Policy

Policy within the context of RPZ refers to a meticulously crafted set of rules and guidelines that dictate the behavior of DNS resolution processes. These policies act as the cornerstone of RPZ implementation, delineating permissible actions such as blocking access to specific domains, redirecting queries to alternative locations, or dynamically modifying DNS responses based on predefined criteria. Such policies serve as the blueprint for ensuring the security, integrity, and efficiency of DNS resolution within an organization’s network infrastructure.

Policy Rule

Policy rules constitute specific conditions or criteria articulated within an RPZ policy framework, serving as the triggers for initiating particular policy actions. These rules are meticulously crafted to address diverse scenarios and may be predicated on factors such as domain names, IP addresses, DNS response codes, or other pertinent attributes.

Policy Action

Policy actions represent the tangible responses enacted by an RPZ in reaction to DNS queries that align with predefined policy rules. These actions are pivotal in shaping the outcome of DNS resolution processes and may include actions such as “drop” (blocking access), “redirect” (routing queries to alternative locations), or “rewrite” (modifying DNS responses) based on the nature of the policy rule triggered.

Malicious Domain

A malicious domain denotes a domain name associated with nefarious or detrimental activities, such as phishing, malware dissemination, or cyberattacks. RPZ policies may incorporate rules designed to proactively block access to known malicious domains, thereby fortifying network security and mitigating potential risks.

Allow Listing (Whitelisting)

Allow Listing embodies the practice of exempting specific domains or IP addresses from RPZ policies, thereby granting unfettered access to designated resources irrespective of prevailing policy rules. This mechanism empowers administrators to ensure unimpeded access to essential services while maintaining stringent security controls.

Deny Listing (Blacklisting)

Conversely, Deny Listing (also referred to as Block Listing) entails the explicit blocking of access to designated domains or IP addresses based on predefined RPZ policies. Deny Listing serves as a proactive measure to thwart unauthorized access to malicious or inappropriate content, safeguarding network integrity and user security.

DNS Firewall

A DNS firewall represents a robust security measure leveraging RPZ policies to filter and regulate DNS traffic. By blocking access to malicious or unauthorized domains, DNS firewalls serve as bulwarks against DNS-based attacks, preserving network integrity and thwarting potential security breaches.

DNSSEC (Domain Name System Security Extensions)

DNSSEC encompasses a suite of extensions to DNS aimed at fortifying its security posture. These extensions imbue DNS responses with enhanced security features such as data origin authentication and data integrity verification. When integrated with RPZ, DNSSEC augments DNS security, bolstering defenses against malicious activities and unauthorized access attempts.

Threat Intelligence

Threat intelligence encompasses curated information pertaining to cybersecurity threats, encompassing malicious domains, IP addresses, and emerging attack vectors. By leveraging threat intelligence feeds, administrators can fortify RPZ policies with real-time insights, enhancing DNS security posture and preemptively mitigating potential threats.

Logging and Reporting

Logging and reporting mechanisms facilitate the systematic recording and analysis of DNS query data generated by RPZ policies. These processes furnish administrators with invaluable insights into DNS activity patterns, potential security threats, and policy effectiveness. By leveraging logging and reporting functionalities, administrators can iteratively refine RPZ policies, fortifying network defenses and safeguarding against evolving threats.

In essence, Response Policy Zones (RPZ) epitomize a potent toolset within the DNS landscape, empowering administrators to orchestrate and enforce robust policies that underpin network security, integrity, and compliance objectives. By wielding RPZ in tandem with comprehensive understanding of DNS principles and security best practices, organizations can fortify their digital infrastructures against a myriad of threats, ensuring seamless connectivity and safeguarding critical assets.