Changing the DNS servers of Public Cloud instances

Objective

The default DNS server configured on instances you create will be the OVHcloud server (213.186.33.99 for example). You can add a secondary server or replace this configuration with your own. However, the DNS servers are configured automatically by a DHCP server and you will not be able to change the DNS configuration by editing the resolv.conf file.

This guide explains how to change the DHCP configuration of an instance in order to change the DNS servers.

Requirements

• A Public Cloud instance in your OVHcloud account
• Administrative access to the instance via SSH or RDP
• Basic networking and administration knowledge

Instructions

Log in to your instance via SSH. Refer to our guide on Connecting to a Public Cloud instance if necessary.

Debian/Ubuntu

Using a text editor of your choice, edit the file /etc/dhcp/dhclient.conf in order to configure the DNS servers you want.

Here you can use different "statements" to add your desired DNS servers. Add the respective line and replace IP1/IP2 with their IP addresses.

• To add DNS servers that will effectively replace the one configured by default, add this line:

supersede domain-name-servers IP1, IP2;

• To add DNS servers that will be preferred to the one configured by default:

prepend domain-name-servers IP1, IP2;

• To add DNS servers that will only be used if the one configured by default is unavailable:

append domain-name-servers IP1, IP2;

Save your changes to the config file and exit the editor.

Check that the configuration has been applied properly with the following command:

cat /etc/resolv.conf

domain openstacklocal
search openstacklocal
nameserver IP1
nameserver IP2

CentOS/Fedora

Check the current configuration with the command nmcli:

nmcli

eth0: connected to System eth0
        "Red Hat Virtio"
        ethernet (virtio_net), FA:16:3E:B6:FB:89, hw, mtu 1500
        ip4 default
        inet4 51.77.205.51/32
        route4 0.0.0.0/0
        route4 51.77.205.51/32
        route4 51.77.204.1/32
        inet6 fe80::f816:3eff:feb6:fb89/64
        route6 ff00::/8
        route6 fe80::/64

lo: non-managed
        "lo"
        loopback (unknown), 00:00:00:00:00:00, sw, mtu 65536

DNS configuration:
        servers: 127.0.0.1 213.186.33.99
        interface: eth0

Retrieve the name of your public interface:

nmcli connection show

NAME         UUID                                  TYPE      DEVICE
System eth0  5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03  ethernet  eth0

Disable the automatic DNS modification and add the IP addresses (replace IP1/IP2) of the DNS servers you want to configure. (Replace System eth0 with the actual value retrieved previously.)

nmcli con mod "System eth0" ipv4.ignore-auto-dns yes
nmcli con mod "System eth0" ipv4.dns "IP1 IP2"

Apply the configuration. (Replace System eth0 with the actual value retrieved previously.)

nmcli con down "System eth0" && nmcli con up "System eth0"

Check that the configuration has been properly applied:

nmcli | grep -E 'DNS|server|interface'

DNS configuration:
        servers: IP1 IP2
        interface: eth0

On Windows

Connect to the instance via remote desktop session or with the VNC console. Refer to our guide on Connecting to a Public Cloud instance if necessary.

Open the Network settings.

Go to your public network adapter’s IPv4 configuration via the control panel.

Add the servers you want to use in the Advanced settings.

Go further

First steps with Public Cloud instances

Changing the hostname of a Public Cloud instance

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