How to Configure IPv6 on a VPS

Objective

IPv6 is the latest version of the Internet Protocol. Each OVHcloud VPS server is delivered with an IPv4 address and an IPv6 address. However, only IPv4 is configured by default. If you need to configure IPv6, it has to be set up manually on your system.

This guide explains how to configure IPv6 on your OVHcloud VPS using various methods.

Requirements

• a Virtual Private Server in your OVHcloud account
• administrative access (root) via SSH or remote desktop (Windows) to your server
• a basic understanding of networking
• access to the OVHcloud Control Panel / to the OVHcloud US API

Instructions

Configuring IPv6 on your VPS is done in multiple steps. At several points in the process you will be prompted to enter commands or to customize configuration files of your server.

Please take note of the following terminology that will be used in code examples and instructions of the guide sections below:

The first step is to identify the IPv6 address and the IPv6 gateway assigned to your server. There are two ways of doing this:

• retrieving the network information via the OVHcloud Control Panel
• retrieving the network information via the OVHcloud API

Via the OVHcloud US Control Panel

Log into the OVHcloud Control Panel, and open the Bare Metal Cloud section. Click Dedicated and virtual servers and then Virtual Private Servers in the services bar on the left-hand side. Then, choose the VPS server concerned.

The IPv6 address and the IPv6 gateway assigned to your server will appear in the IP section of the Home tab. Once you have copied them, continue with applying the IPv6 configuration.

Via the OVHcloudAPI

On the OVHcloud API page click on Login in the top-right corner. On the following page, enter the credentials of your OVHcloud account.

Use this call to retrieve the IPv6 address assigned to your server:

Once you have retrieved these addresses, continue with applying the IPv6 configuration.

Step 2: Apply the IPv6 configuration

Once you have gathered the necessary information for the IPv6 configuration, log in to your VPS via SSH. If you require assistance, please refer to this guide: Getting Started with SSH.

There are several ways to apply the IPv6 configuration. Use whichever method best suits your situation and requirements:

• Non-persistent application
• Persistent application on Debian and its derivatives
• Persistent application on Red Hat and its derivatives
• Persistent application on Windows Server

Non-persistent application

Connect to your server via SSH and enter the following commands. Take care to tailor these with:

• the network information, retrieved in the previous step (YOUR_IPV6, IPV6_PREFIX and IPV6_GATEWAY)
• the network interface (if your server is not using eth0)

# ip addr add YOUR_IPV6/IPV6_PREFIX dev eth0
# ip -6 route add IPV6_GATEWAY dev eth0
# ip -6 route add default via IPV6_GATEWAY dev eth0

Persistent application on Debian and its derivatives (Ubuntu, Crunchbang, SteamOS, etc.)

There are two ways to configure your network depending on the operating system installed on your server:

• for Debian 8 and earlier, Ubuntu 16.04 and earlier: use the method based on the interfaces files

• for Debian 9, Ubuntu 17.04 and later: use the method based on the Netplan configuration

In some cases (such as Debian 9), the appropriate method may not be the one specified above. To make sure, browse your system to check which one is active. Visit https://netplan.io/ for more information, if necessary.
Moreover, keep in mind that the exact file names may vary.

Configuration of interfaces files

The best practice approach is to create a configuration file in the directory /etc/network/interfaces.d/:

# nano /etc/network/interfaces.d/51-cloud-init-ipv6.cfg

This allows you to separate the IPv6 configuration and easily revert the changes in case of an error.

Add the following lines to the file. Replace the generic elements (i.e. YOUR_IPV6, IPV6_PREFIX and IPV6_GATEWAY) as well as the network interface (if your server is not using eth0) with your specific values.

auto eth0
iface eth0 inet6 static
mtu 1500
address YOUR_IPV6
netmask IPV6_PREFIX
post-up /sbin/ip -6 route add IPV6_GATEWAY dev eth0
post-up /sbin/ip -6 route add default via IPV6_GATEWAY dev eth0
pre-down /sbin/ip -6 route del default via IPV6_GATEWAY dev eth0
pre-down /sbin/ip -6 route del IPV6_GATEWAY dev eth0

Then restart your network service with one of the following commands:

# service networking restart

# systemctl restart networking

Alternatively, you can add the configuration above to one of the following files (with sudo privileges), depending on the generation of the operating system installed on the server:

• the /etc/network/interfaces file
• the /etc/network/interfaces.d/50-cloud-init.cfg file

We recommend that you back up up the relevant configuration file. For example, use the following command:

# cp /etc/network/interfaces /etc/network/interfaces.back

You will then be able to revert the changes, using the commands below:

# rm -f /etc/network/interfaces
# cp /etc/network/interfaces.back /etc/network/interfaces

Configuration using Netplan

The network configuration files are located in the /etc/netplan/ directory. We recommend that you start by backing up the relevant configuration file. In this case, copy the 50-cloud-init.yaml file using the following commands:

# cd /etc/netplan/
# mkdir backup
# cp 50-cloud-init.yaml backup/50-cloud-init.yaml

You will then be able to revert the changes, using the commands below:

# rm -f /etc/netplan/50-cloud-init.yaml
# cp /etc/netplan/backup/50-cloud-init.yaml /etc/netplan/50-cloud-init.yaml

Before editing it, create a copy of the IPv6 configuration file:

# cd /etc/netplan
# cp 50-cloud-init.yaml 51-cloud-init-ipv6.yaml

Then edit the 51-cloud-init-ipv6.yaml file, adding the IPv6 configuration of your server. Replace the generic elements (i.e. YOUR_IPV6, IPV6_PREFIX and IPV6_GATEWAY) as well as the network interface (if your server is not using eth0) with your specific values.

network:
    version: 2
    ethernets:
        eth0:
            dhcp6: no
            match:
              name: eth0
            addresses:
              - "YOUR_IPV6/IPv6_PREFIX"
            gateway6: "IPv6_GATEWAY"
            routes:
              - to: "IPv6_GATEWAY"
                scope: link

You can test your configuration using this command:

# netplan try

If it is correct, apply it using the following command:

# netplan apply

Persistent application on Red Hat and its derivatives (CentOS, ClearOS, etc.)

The network configuration files are located in the /etc/sysconfig/network-scripts/ directory. We recommend that you start by backing up the relevant configuration file. For example, copy the ifcfg-eth0 file using the following commands. Remember to replace eth0 with your actual interface if necessary.

# cd /etc/sysconfig/network-scripts/
# mkdir backup
# cp ifcfg-eth0 backup/ifcfg-eth0

You will then be able to revert the changes, using the commands below:

# rm -f /etc/sysconfig/network-scripts/ifcfg-eth0
# cp /etc/sysconfig/network-scripts/backup/ifcfg-eth0 /etc/sysconfig/network-scripts/ifcfg-eth0

Then edit the ifcfg-eth0 file, adding the IPv6 configuration of your server. Replace the generic elements (i.e. YOUR_IPV6, IPV6_PREFIX and IPV6_GATEWAY) with your specific values.

IPV6INIT=yes
IPV6ADDR=YOUR_IPV6/IPV6_PREFIX
IPV6_DEFAULTGW=IPV6_GATEWAY

On CentOS 7, you have to create a routing file in addition to the steps above:

• Create a file (with sudo privileges), indicating the default IPv6 routes:

# touch /etc/sysconfig/network-scripts/route6-eth0

• Edit the file and add the lines below. Replace the generic elements (IPV6_GATEWAY and eth0 interface, if necessary) with your specific values.

IPV6_GATEWAY dev eth0
default via IPV6_GATEWAY

Finally, restart your network service to allow the system to apply the new configuration with one of the following commands:

# service networking restart

# systemctl restart networking

Persistent application on Windows Server

By default, IPv6 is not configured on Windows Servers. To enable it, open the Control Panel and click on View network status and tasks, then on Change adapter settings.

Click on Ethernet to open the settings and click on the Properties button to view the Ethernet Properties.

Select Internet Protocol Version 6 (TCP/IPv6), then click on the Properties button.

In the IPv6 Properties window, select Use the following IPv6 address. Enter the IP addresses which you have retrieved in the first step.

You also have the option of entering the IPv6 DNS resolvers of your choice under Use the following DNS server addresses. This is not mandatory if the DNS resolvers of the IPv4 configuration are already functional.

Finally, tick the Validate settings upon exit box and click the OK button to validate your changes. An error message may appear if the specified gateway is not on the same IPv6 subnet (/128 and /64 for example). You can ignore this message and continue to the next step regardless.

Step 3: Verify the configuration and test the connection

To verify that the configuration is functional, there are several possible commands, depending on the operating system.

• For a GNU/Linux-based system, here are two examples for the eth0 interface (to be adapted if necessary):

# ip -6 addr show eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 1000
    inet6 2001:xxxx:xxxx:xxxx:xxxx:xxxx:zzzz/128 scope global
       valid_lft forever preferred_lft forever
    inet6 fe80::f816:3eff:fec0:c336/64 scope link
       valid_lft forever preferred_lft forever

# ifconfig eth0
eth0      Link encap:Ethernet  HWaddr ab:cd:ef:gf:ij:kl
          inet addr:aa.bb.cc.dd  Bcast:aa.bb.cc.ee  Mask:255.255.255.255
          inet6 addr: 2001:xxxx:xxxx:xxxx:xxxx:xxxx:zzzz/128 Scope:Global
          inet6 addr: fe80::f816:3eff:fec0:c336/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          [...]

To test the connection, you can use the following command:

# ping6 proof.ovh.net

• For a Windows-based system, use the following command:

# ipconfig

Windows IP Configuration

Ethernet adapter Ethernet:

   Connection-specific DNS Suffix  . : openstacklocal
   IPv6 Address. . . . . . . . . . . : 2001:xxxx:xxxx:xxxx::zzzz
   Link-local IPv6 Address . . . . . : fe80::d928:7a00:5ba6:951b%3
   IPv4 Address. . . . . . . . . . . : 51.xxx.xxx.xxx
   Subnet Mask . . . . . . . . . . . : 255.255.255.255
   Default Gateway . . . . . . . . . : 2001:xxxx:xxxx:xxxx::y
                                       51.xxx.xxx.y

To test the connection, you can use the following command:

# ping -6 proof.ovh.net

You can also test the connection to another remote server. However, it is necessary for IPv6 to be active on the remote server for this operation to work.

Step 4: Disable Cloud-init network management (optional)

Cloud-init is a package installed by default on a VPS. It functions as a framework to run a script after initially creating your server or rebooting it. The mechanics in place allow the underlying OpenStack infrastructure to inject scripts into the Cloud-init environment and therefore the server configuration.

Depending on the operating system, Cloud-init will manage: the network, the hostname, the resolv.conf file, or the automatic partitioning of the hard disk, in case of an upgrade.

In the case of newer distributions (such as CentOS, Debian 9, Ubuntu 16.x, and later), the default configuration of Cloud-init might sometimes automatically reset the network configuration when the server starts up.

This is relevant for specific use cases in which it is recommended to avoid the reset by disabling automatic network management in Cloud-init. To do this, use the following command to create a file /etc/cloud/cloud.cfg.d/98-disable-network-config.cfg with the value network: {config: disabled}:

# echo "network: {config: disabled}" > /etc/cloud/cloud.cfg.d/98-disable-network-config.cfg

In order to return to automatic management of your network by Cloud-init, delete the newly created file or move it to another directory.