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DNS policies

When a user makes a DNS request to Gateway, Gateway matches the request against the content or security categories you have set up for your organization. If the domain does not belong to any blocked categories, or if it matches an Override policy, the user’s client receives the DNS resolution and initiates an HTTP connection.

A DNS policy consists of an Action as well as a logical expression that determines the scope of the action. To build an expression, you need to choose a Selector and an Operator, and enter a value or range of values in the Value field.

When creating a DNS policy, you can select as many security risk categories and content categories as needed to fully secure your network. Unless a more specific selector is configured in a policy (for example, user email or source IP address), then the policy will be evaluated against all DNS queries that reach Gateway from your organization.

​​ Actions

Just like actions in HTTP policies, actions in DNS policies allow you to choose what to do with a given set of elements. You can assign one action per policy.

These are the action types you can choose from:

​​ Allow

Policies with Allow actions allow DNS queries to reach destinations you specify within the Selector and Value fields. For example, the following configuration allows DNS queries to reach domains we categorize as belonging to the Education content category:

SelectorOperatorValueAction
Content CategoriesInEducationAllow

​​ Disable DNSSEC validation

When you select Disable DNSSEC validation, Gateway will resolve DNS queries even if the cryptographic signature for the DNS record cannot be validated. We do not recommend disabling DNSSEC validation unless you know that the validation failure is due to DNSSEC configuration issues and not malicious attacks.

​​ Block

Policies with Block actions block DNS queries to reach destinations you specify within the Selector and Value fields. For example, the following configuration blocks DNS queries from reaching domains we categorize as belonging to the Adult Themes content category:

SelectorOperatorValueAction
Content CategoriesInAdult ThemesBlock

​​ Custom block page

When choosing the Block action, toggle the Display custom block page setting to respond to queries with a block page and to specify the message you want to display to users who navigate to blocked websites. If disabled, Gateway will respond to blocked queries with 0.0.0.0. For more information, refer to the dedicated documentation on customizing the block page.

​​ Override

Policies with Override actions allow you to respond to all DNS queries for a given domain to another destination. For example, you can provide a custom response IP of 1.2.3.4 for all queries to www.example.com with the following policy:

SelectorOperatorValueActionOverride Hostname
HostnameIswww.example.comOverride1.2.3.4

​​ SafeSearch

SafeSearch is a feature of search engines that helps you filter explicit or offensive content. When you enable SafeSearch, the search engine filters explicit or offensive content and returns search results that are safe for children or at work.

You can use Cloudflare Gateway to enable SafeSearch on search engines like Google, Bing, Yandex, YouTube and DuckDuckGo. For example, to enable SafeSearch for Google, you can create the following policy:

SelectorOperatorValueAction
DomainIsgoogle.comSafeSearch

​​ YouTube Restricted Mode

Similarly, you can enforce YouTube Restricted mode by choosing the Youtube Restricted action. YouTube Restricted Mode is an automated filter for adult and offensive content built into YouTube. To enable Youtube Restricted Mode, you could set up a policy like the following:

SelectorOperatorValueAction
DNS DomainIsyoutube.comYouTube Restricted

This setup ensures users will be blocked from accessing offensive sites using DNS.

​​ Selectors

Gateway matches DNS traffic against the following selectors, or criteria:

​​ Application

You can apply DNS policies to a growing list of popular web applications. Refer to the Application and app types page for more information.

UI nameAPI example
Applicationany(app.ids[*] in {505}

​​ Authoritative Nameserver IP

Use this selector to match against the IP address of the authoritative name server IP address.

UI nameAPI example
Authoritative Nameserver IPdns.authoritative_ns_ips == 198.51.100.0

​​ Content Categories

Use this selector to block domains (and optionally, IP addresses) belonging to specific content categories.

UI nameAPI example
Content Categoriesany(dns.content_category[*] in {1})

​​ DNS CNAME Record

Use this selector to filter DNS responses by their CNAME records.

UI nameAPI example
DNS CNAME Response Valueany(dns.response.cname[*] in {"www.apple.com.edgekey.net"})

​​ DNS MX Record

Use this selector to filter DNS responses by their MX records.

UI nameAPI example
DNS MX Response Valueany(dns.response.mx[*] in {"gmail-smtp-in.l.google.com"})

​​ DNS PTR Record

Use this selector to filter DNS responses by their PTR records.

UI nameAPI example
DNS PTR Response Valueany(dns.response.ptr[*] in {"255.2.0.192.in-addr.arpa"})

​​ DNS Resolver IP

Use this selector to apply policies to DNS queries that arrived to your Gateway Resolver IP address aligned with a registered DNS location. For most Gateway customers, this is an IPv4 AnyCast address and policies created using this IPv4 address will apply to all DNS locations. However, each DNS location has a dedicated IPv6 address and some Gateway customers have been supplied with a dedicated IPv4 address — these both can be used to apply policies to specific registered DNS locations.

UI nameAPI example
DNS Resolver IPany(dns.resolved_ip[*] == 198.51.100.0)

​​ DNS TXT Record

Use this selector to filter DNS responses by their TXT records.

UI nameAPI example
DNS TXT Response Valueany(dns.response.txt[*] in {"your_text"})

​​ DNS Location

Use this selector to apply DNS policies to a specific Gateway DNS location or set of locations.

UI nameAPI example
DNS Locationdns.location in {"location_uuid_1" "location_uuid_2"}

​​ DOH Subdomain

Use this selector to match against DNS queries that arrive via DNS-over-HTTPS (DoH) destined for the DoH endpoint configured for each DNS location. For example, a DNS location with a DoH endpoint of abcdefg.cloudflare-gateway.com could be used in a DNS rule by choosing the DoH Subdomain selector and inputting a value of abcdefg.

UI nameAPI example
DOH Subdomaindns.doh_subdomain == "abcdefg"

​​ Domain

Use this selector to match against a domain and all subdomains — for example, if you want to block example.com and subdomains such as www.example.com.

UI nameAPI example
Domainany(dns.domains[*] == "example.com")

​​ Host

Use this selector to match against only the hostname specified. — for example, if you want to block test.example.com but not example.com or www.test.example.com.

UI nameAPI example
Hostdns.fqdn == "test.example.com"

​​ Query Record Type

Use this selector to choose the DNS resource record type that you would like to apply policies against — for example, you can choose to block A records for a domain but not MX records.

UI nameAPI example
Query Record Typedns.query_rtype == "TXT"

​​ Resolved Continent

Use this selector to filter based on the continent that the query resolves to. Geolocation is determined from the IP address in the response. To specify a continent, enter its two-letter code into the Value field:

  • AF – Africa
  • AN – Antarctica
  • AS – Asia
  • EU – Europe
  • NA – North America
  • OC – Oceania
  • SA – South America
  • T1 – Tor network
UI nameAPI example
Resolved Continent IP Geolocationdns.dst.geo.continent == "EU"

​​ Resolved Country

Use this selector to filter based on the country that the query resolves to. Geolocation is determined from the IP address in the response. To specify a country, enter its ISO 3166-1 Alpha 2 code in the Value field.

UI nameAPI example
Resolved Country IP Geolocationdns.dst.geo.country == "RU"

​​ Resolved IP

Use this selector to filter based on the IP addresses that the query resolves to.

UI nameAPI example
Resolved IPany(dns.resolved_ips[*] == 198.51.100.0)

​​ Security Categories

Use this selector to block domains (and optionally, IP addresses) belonging to specific security categories.

UI nameAPI example
Security Categoriesany(dns.security_category[*] in {1})

​​ Source Continent

Use this selector to filter based on the continent where the query arrived to Gateway from. Geolocation is determined from the source IP address. To specify a continent, enter its two-letter code into the Value field:

  • AF – Africa
  • AN – Antarctica
  • AS – Asia
  • EU – Europe
  • NA – North America
  • OC – Oceania
  • SA – South America
  • T1 – Tor network
UI nameAPI example
Source Continent IP Geolocationdns.src.geo.continent == "EU"

​​ Source Country

Use this selector to filter based on the country where the query arrived to Gateway from. Geolocation is determined from the source IP address. To specify a country, enter its ISO 3166-1 Alpha 2 code in the Value field.

UI nameAPI example
Source Country IP Geolocationdns.src.geo.country == "RU"

​​ Source IP

Use this selector to apply DNS policies to a specific source IP address that queries arrive to Gateway from — for example, this could be the WAN IP address of the stub resolver used by an organization to send queries upstream to Gateway.

UI nameAPI example
Source IPdns.src_ip == 198.51.100.0

​​ Users

The User, User Group, and SAML Attributes selectors require Gateway with WARP mode to be enabled in the Zero Trust WARP client, and the user to be enrolled in the organization via the WARP client. For more information on identity-based selectors, refer to the Identity-based policies page.

​​ Operators

Operators are the way Gateway matches traffic to a selector. When you choose a Selector in the dashboard policy builder, the Operator dropdown menu will display the available options for that selector.

OperatorMeaning
isequals the defined value
is notdoes not equal the defined value
inmatches at least one of the defined values
not indoes not match any of the defined values
in listin a pre-defined list of values
not in listnot in a pre-defined list of values
matches regexregex evaluates to true
does not match regexregex evaluates to false
greater thanexceeds the defined number
greater than or equal toexceeds or equals the defined number
less thanbelow the defined number
less than or equal tobelow or equals the defined number

​​ Value

You can input a single value or use regular expressions to specify a range of values.

Gateway uses Rust to evaluate regular expressions. The Rust implementation is slightly different than regex libraries used elsewhere. For more information, refer to our guide for Using wildcards in subdomains and paths.

For example, if you want to match multiple domains, you could use the pipe symbol (|) as an OR operator. In Gateway, you do not need to use an escape character (\) before the pipe symbol. The following configuration blocks requests to two hosts if either appears in a request header:

SelectorOperatorValueAction
HostMatches regex`.*whispersystems.org.*signal.org`

To evaluate if your regex matches, you can use Rustexp.