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Resolver policies

Beta

By default, Gateway sends DNS requests to 1.1.1.1, Cloudflare’s public DNS resolver, for resolution. Enterprise users can instead create Gateway policies to route DNS queries to custom resolvers.

​​ Use cases

You may use resolver policies if you require access to non-publicly routed domains, such as private network services or internal resources. You may also use resolver policies if you need to access a protected DNS service or want to simplify DNS management for multiple locations.

If your resolver is only reachable by a client device and not by Gateway via a Cloudflare tunnel, Magic WAN tunnel, or other public Internet connections, you should configure Local Domain Fallback for your device. If both Local Domain Fallback and resolver policies are configured for the same device, Cloudflare will apply your client-side Local Domain Fallback rules first.

​​ Resolver connections

Resolver policies support TCP and UDP connections. Custom resolvers can point to the Internet via IPv4 or IPv6, or to a private network service, such as a Magic tunnel. Policies default to port 53. You can change which port your resolver uses by customizing it in your policy.

You can protect your authoritative nameservers from DDoS attacks by enabling DNS Firewall.

​​ Available endpoints

Resolver policies can route queries for resolution from the following DNS endpoints:

Gateway will filter, resolve, and log your queries regardless of endpoint.

​​ Create a resolver policy

  1. In Zero Trust, go to Gateway > Resolver policies.

  2. Select Add a policy.

  3. Create an expression for your desired traffic. For example, you can resolve a hostname for an internal service:

    SelectorOperatorValue
    Hostininternal.example.com
  4. In Select DNS resolver, choose Configure custom DNS resolvers.

  5. Enter the IP addresses of your custom DNS resolver.

  6. In Network, choose whether to route queries publicly (to the Internet) or privately (to a private network service).

  7. (Optional) Enter a custom port for each IP address.

  8. Select Create policy.

Custom resolvers are saved to your account for future use. You can add up to 10 IPv4 and 10 IPv6 addresses to a policy.

When a user’s query matches a resolver policy, Gateway will send the query to your listed resolvers in the following order:

  1. Public resolvers
  2. Private resolvers behind the default virtual network for your account
  3. Private resolvers behind a custom virtual network

Gateway will cache the fastest resolver for use in subsequent queries. Resolver priority is cached on a per user basis for each data center.

For more information on creating a DNS policy, refer to DNS policies.

​​ Selectors

​​ Content Categories

Use this selector to filter domains belonging to specific content categories.

UI nameAPI exampleEvaluation phase
Content Categoriesany(dns.content_category[*] in {1})Before DNS resolution

​​ 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 exampleEvaluation phase
DNS Resolver IPany(dns.resolved_ip[*] == 198.51.100.0)Before DNS resolution

​​ 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, you can use a DNS location with a DoH endpoint of abcdefg.cloudflare-gateway.com by choosing the DoH Subdomain selector and inputting a value of abcdefg.

UI nameAPI exampleEvaluation phase
DOH Subdomaindns.doh_subdomain == "abcdefg"Before DNS resolution

​​ Domain

Use this selector to match against a domain and all subdomains. For example, you can match example.com and its subdomains, such as www.example.com.

UI nameAPI exampleEvaluation phase
Domainany(dns.domains[*] == "example.com")Before DNS resolution

​​ Host

Use this selector to match against only the hostname specified. For example, you can match test.example.com but not example.com or www.test.example.com.

UI nameAPI exampleEvaluation phase
Hostdns.fqdn == "test.example.com"Before DNS resolution

​​ Location

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

UI nameAPI exampleEvaluation phase
Locationdns.location in {"location_uuid_1" "location_uuid_2"}Before DNS resolution

​​ 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 match A records for a domain but not MX records.

UI nameAPI exampleEvaluation phase
Query Record Typedns.query_rtype == "TXT"Before DNS resolution

​​ Security Categories

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

UI nameAPI exampleEvaluation phase
Security Categoriesany(dns.security_category[*] in {1})Before DNS resolution

​​ Source Continent

Use this selector to filter based on the continent where the query arrived to Gateway from.

Geolocation is determined from the device’s public IP address (typically assigned by the user’s ISP). To specify a continent, enter its two-letter code into the Value field:

ContinentCode
AfricaAF
AntarcticaAN
AsiaAS
EuropeEU
North AmericaNA
OceaniaOC
South AmericaSA
Tor networkT1
UI nameAPI exampleEvaluation phase
Source Continent IP Geolocationdns.src.geo.continent == "North America"Before DNS resolution

​​ Source Country

Use this selector to filter based on the country where the query arrived to Gateway from.

Geolocation is determined from the device’s public IP address (typically assigned by the user’s ISP). To specify a country, enter its ISO 3166-1 Alpha-2 code in the Value field.

UI nameAPI exampleEvaluation phase
Source Country IP Geolocationdns.src.geo.country == "RU"Before DNS resolution

​​ Source IP

Use this selector to apply policies to the source IP address of DNS queries. For example, this could be the WAN IP address of the stub resolver used by your organization to send queries to Gateway.

UI nameAPI exampleEvaluation phase
Source IPdns.src_ip == 198.51.100.0Before DNS resolution

​​ Users

Identity-based selectors include:

  • SAML Attributes
  • User Email
  • User Group Emails
  • User Group IDs
  • User Group Names
  • User Name

To use identity-based selectors, enable Gateway with WARP in the Zero Trust WARP client and enroll your user in your organization. For more information, refer to Identity-based policies.

​​ Comparison operators

Comparison 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 Wildcards.

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.orgBlock

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

​​ Logical operators

To evaluate multiple conditions in an expression, select the And logical operator. These expressions can be compared further with the Or logical operator.

OperatorMeaning
Andmatch all of the conditions in the expression
Ormatch any of the conditions in the expression

The Or operator will only work with conditions in the same expression group. For example, you cannot compare conditions in Traffic with conditions in Identity.