If you see this warning, first check to see if you use `dnsmasq`:

```console
$ ps aux | grep dnsmasq
```

If your container needs to resolve hosts which are internal to your network, the
public nameservers aren't adequate. You have two choices:

- Specify DNS servers for Docker to use.
- Turn off `dnsmasq`.

  Turning off `dnsmasq` adds the IP addresses of actual DNS nameservers to
  `/etc/resolv.conf`, and you lose the benefits of `dnsmasq`.

You only need to use one of these methods.

### Specify DNS servers for Docker

The default location of the configuration file is `/etc/docker/daemon.json`. You
can change the location of the configuration file using the `--config-file`
daemon flag. The following instruction assumes that the location of the
configuration file is `/etc/docker/daemon.json`.

1. Create or edit the Docker daemon configuration file, which defaults to
   `/etc/docker/daemon.json` file, which controls the Docker daemon
   configuration.

   ```console
   $ sudo nano /etc/docker/daemon.json
   ```

2. Add a `dns` key with one or more DNS server IP addresses as values.

   ```json
   {
     "dns": ["8.8.8.8", "8.8.4.4"]
   }
   ```

   If the file has existing contents, you only need to add or edit the `dns`
   line. If your internal DNS server can't resolve public IP addresses, include
   at least one DNS server that can. Doing so allows you to connect to Docker
   Hub, and your containers to resolve internet domain names.

   Save and close the file.

3. Restart the Docker daemon.

   ```console
   $ sudo service docker restart
   ```

4. Verify that Docker can resolve external IP addresses by trying to pull an
   image:

   ```console
   $ docker pull hello-world
   ```

5. If necessary, verify that Docker containers can resolve an internal hostname
   by pinging it.

   ```console
   $ docker run --rm -it alpine ping -c4 <my_internal_host>

   PING google.com (192.168.1.2): 56 data bytes
   64 bytes from 192.168.1.2: seq=0 ttl=41 time=7.597 ms
   64 bytes from 192.168.1.2: seq=1 ttl=41 time=7.635 ms
   64 bytes from 192.168.1.2: seq=2 ttl=41 time=7.660 ms
   64 bytes from 192.168.1.2: seq=3 ttl=41 time=7.677 ms
   ```

### Turn off `dnsmasq`

{{< tabs >}}
{{< tab name="Ubuntu" >}}

If you prefer not to change the Docker daemon's configuration to use a specific
IP address, follow these instructions to turn off `dnsmasq` in NetworkManager.

1. Edit the `/etc/NetworkManager/NetworkManager.conf` file.

2. Comment out the `dns=dnsmasq` line by adding a `#` character to the beginning
   of the line.

   ```text
   # dns=dnsmasq
   ```

   Save and close the file.

3. Restart both NetworkManager and Docker. As an alternative, you can reboot
   your system.

   ```console
   $ sudo systemctl restart network-manager
   $ sudo systemctl restart docker
   ```

{{< /tab >}}
{{< tab name="RHEL, CentOS, or Fedora" >}}

To turn off `dnsmasq` on RHEL, CentOS, or Fedora:

1. Turn off the `dnsmasq` service:

   ```console
   $ sudo systemctl stop dnsmasq
   $ sudo systemctl disable dnsmasq
   ```

2. Configure the DNS servers manually using the
   [Red Hat documentation](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/9/html/configuring_and_managing_networking/configuring-the-order-of-dns-servers_configuring-and-managing-networking).

{{< /tab >}}
{{< /tabs >}}

### Docker networks disappearing

If a Docker network, such as the `docker0` bridge or a custom network, randomly
disappears or otherwise appears to be working incorrectly, it could be because
another service is interfering with or modifying Docker interfaces. Tools that
manage networking interfaces on the host are known to sometimes also
inappropriately modify Docker interfaces.

Refer to the following sections for instructions on how to configure your
network manager to set Docker interfaces as un-managed, depending on the
network management tools that exist on the host:

- If `netscript` is installed, consider [uninstalling it](#uninstall-netscript)