---
title: Test DNS filtering · Cloudflare Zero Trust docs
description: This section covers how to validate your Gateway DNS configuration.
lastUpdated: 2025-05-27T21:46:13.000Z
chatbotDeprioritize: false
source_url:
  html: https://developers.cloudflare.com/cloudflare-one/policies/gateway/dns-policies/test-dns-filtering/
  md: https://developers.cloudflare.com/cloudflare-one/policies/gateway/dns-policies/test-dns-filtering/index.md
---

This section covers how to validate your Gateway DNS configuration.

## Prerequisites

Before you start, make sure you are connected to a network that is associated with the [DNS location](https://developers.cloudflare.com/cloudflare-one/connections/connect-devices/agentless/dns/locations/) where the policy is applied.

## Test a DNS policy

Once you have created a DNS policy to block a domain, you can use either `dig` or `nslookup` to see if the policy is working as intended.

For example, if you created a policy to block `example.com`, you can do the following to see if Gateway is successfully blocking `example.com`:

1. Open your terminal.

2. Type `dig example.com` (`nslookup example.com` if you are using Windows) and press **Enter**.

3. If the [block page](https://developers.cloudflare.com/cloudflare-one/policies/gateway/block-page/) is turned off for the policy, you should see `REFUSED` in the answer section:

   ```sh
   dig example.com
   ```

   ```sh
   ; <<>> DiG 9.10.6 <<>> example.com
   ;; global options: +cmd
   ;; Got answer:
   ;; ->>HEADER<<- opcode: QUERY, status: REFUSED, id: 6503
   ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0


   ;; QUESTION SECTION:
   ;example.com.                   IN      A


   ;; Query time: 46 msec
   ;; SERVER: 172.64.36.1#53(172.64.36.1)
   ;; WHEN: Tue Mar 10 20:22:18 CDT 2020
   ;; MSG SIZE  rcvd: 29
   ```

   If the [block page](https://developers.cloudflare.com/cloudflare-one/policies/gateway/block-page/) is enabled for the policy, you should see `NOERROR` in the answer section with `162.159.36.12` and `162.159.46.12` as the answers:

   ```sh
   dig example.com
   ```

   ```sh
   ; <<>> DiG 9.10.6 <<>> example.com
   ;; global options: +cmd
   ;; Got answer:
   ;; ->>HEADER<<- opcode: QUERY, status: NOERROR id: 14531
   ;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1


   ;; OPT PSEUDOSECTION:
   ; EDNS: version: 0, flags:; udp: 1452
   ;; QUESTION SECTION:
   ;example.com.                   IN      A


   ;;ANSWER SECTION:
   example.com.            60      IN      A                  162.159.36.12
   example.com.            60      IN      A                  162.159.46.12


   ;; Query time: 53 msec
   ;; SERVER: 172.64.36.1#53(172.64.36.1)
   ;; WHEN: Tue Mar 10 20:19:52 CDT 2020
   ;; MSG SIZE  rcvd: 83
   ```

### Test a security or content category

If you are blocking a [security category](https://developers.cloudflare.com/cloudflare-one/policies/gateway/dns-policies/#security-categories) or a [content category](https://developers.cloudflare.com/cloudflare-one/policies/gateway/dns-policies/#content-categories), you can test that the policy is working by using the [test domain](#common-test-domains) associated with each category.

Once you have configured your Gateway policy to block the category, the test domain will show a block page when you attempt to visit the domain in your browser, or will return `REFUSED` when you perform `dig` using the command-line interface.

#### Test domain format

* **One-word category** — For categories with one-word names (for example, *Malware*), the test domain uses the following format:

  ```txt
  <NAME_OF_CATEGORY>.testcategory.com
  ```

* **Multi-word category** — For categories with multiple words in the name (for example, *Parked & For Sale Domains*), the test domain uses the following format:

  * Remove any spaces between the words
  * Replace `&` with `and`
  * Lowercase all letters

#### Common test domains

| Category | Test domain |
| - | - |
| *Anonymizer* | `anonymizer.testcategory.com` |
| *Command and Control & Botnet* | `commandandcontrolandbotnet.testcategory.com` |
| *compromised Domain* | `compromiseddomain.testcategory.com` |
| *Cryptomining* | `cryptomining.testcategory.com` |
| *Malware* | `malware.testcategory.com` |
| *New Domains* | `newdomains.testcategory.com` |
| *Parked & For Sale Domains* | `parkedandforsaledomains.testcategory.com` |
| *Phishing* | `phishing.testcategory.com` |
| *Potentially Unwanted Software* | `potentiallyunwantedsoftware.testcategory.com` |
| *Private IP Address* | `privateipaddress.testcategory.com` |
| *Spam* | `spam.testcategory.com` |
| *Spyware* | `spyware.testcategory.com` |
| *Unreachable* | `unreachable.testcategory.com` |

## Test EDNS configuration

If you [enabled EDNS client subnet](https://developers.cloudflare.com/cloudflare-one/connections/connect-devices/agentless/dns/locations/) for your DNS location, you can validate EDNS as follows:

1. Obtain your DNS location's DOH subdomain:

   1. In [Zero Trust](https://one.dash.cloudflare.com), go to **Gateway** > **DNS locations**.
   2. Select the DNS location you are testing.
   3. Note the value of **DNS over HTTPS**.

2. Open a terminal and run the following command:

   ```sh
   curl 'https://<DOH_SUBDOMAIN>.cloudflare-gateway.com/dns-query?type=TXT&name=o-o.myaddr.google.com' -H 'Accept: application/dns-json' | json_pp
   ```

   The output should contain your EDNS client subnet:

   ```json
   {
     "AD": false,
     "Answer": [
       {
         "TTL": 60,
         "data": "\"108.162.218.211\"",
         "name": "o-o.myaddr.google.com",
         "type": 16
       },
       {
         "TTL": 60,
         "data": "\"edns0-client-subnet 136.62.0.0/24\"",
         "name": "o-o.myaddr.google.com",
         "type": 16
       }
     ],
     "CD": false,
     "Question": [
       {
         "name": "o-o.myaddr.google.com",
         "type": 16
       }
     ],
     "RA": true,
     "RD": true,
     "Status": 0,
     "TC": false
   }
   ```

3. To verify your EDNS client subnet, obtain your source IP address:

   ```sh
   curl ifconfig.me
   ```

   ```sh
   136.62.12.156%
   ```

   The source IP address should fall within the /24 range specified by your EDNS client subnet.

## Clear DNS cache

Modern web browsers and operating systems are designed to cache DNS records for a set amount of time. When a request is made for a DNS record, the browser cache is the first location checked for the requested record. A DNS policy may not appear to work if the response is already cached.

To clear your DNS cache:

ChromeOS

1. Go to `chrome://net-internals/#dns`.
2. Select **Clear host cache**.

Windows

1. Open the admin command prompt or PowerShell.
2. Run the following command:

```bash
ipconfig /flushdns
```

macOS

1. Open Terminal.
2. Run the following commands:

```sh
sudo killall -HUP mDNSResponder
sudo killall mDNSResponderHelper
sudo dscacheutil -flushcache
```
