Configuring Ubuntu to Use a Gateway Outside of the Assigned V6 prefix Network Print

Introduction

This guide will help you configure your Ubuntu system to use an IPv6 gateway outside of the assigned /48 network. This is particularly useful for ensuring proper network routing when the default installation setup does not support this configuration.

Prerequisites

• An Ubuntu system with Netplan installed.
• Basic knowledge of accessing and editing configuration files using a terminal.
• Your specific network details (IPv4 and IPv6 addresses, gateways, MAC address, etc.).

Default Netplan Configuration

When your system installs, the default Netplan configuration might look something like this:

network:
ethernets:
id0:
addresses:
- 23.172.120.XXX/24
- 2602:f96d:XXX:XX::1/64
gateway4: 23.172.120.1
gateway6: 2602:f96d::1
match:
macaddress: BC:XX:11:XX:85:6C
nameservers:
addresses:
- 1.1.1.1
- 8.8.8.8
- 1.0.0.1
renderer: networkd
version: 2

Problem

In the configuration above, the IPv6 gateway (2602:f96d::1) is outside the assigned /48 network (2602:f96d:XX::1/48), causing routing issues.

Solution

To resolve this, you need to add specific routes to your Netplan configuration. Follow the steps below:

1. Open the Netplan configuration file:
   sudo nano /etc/netplan/01-netcfg.yaml
   Adjust the filename if your configuration file has a different name.

2. Modify the Netplan configuration:
   Update your configuration to include specific routes for IPv6. Your updated configuration should look like this:
   
   network:
ethernets:
id0:
addresses:
- 23.172.120.XX/24
- 2602:f96d:XX:xx::1/48
gateway4: 23.172.120.1
match:
macaddress: BC:24:11:3C:85:6C
nameservers:
addresses:
- 1.1.1.1
- 8.8.8.8
- 1.0.0.1
routes:
- to: "2602:f96d::1/128"
scope: link
- to: "::/0"
via: "2602:f96d::1"
on-link: true
renderer: networkd
version: 2
   
   

Explanation:

• The routes section is added to specify the routes.
• The first route specifies that the gateway (2602:f96d::1) is on the link, meaning it is directly reachable on the local network.
• The second route sets the default route for all IPv6 traffic (::/0) to go through the specified gateway (2602:f96d::1), and the on-link: true option ensures that the system considers the gateway to be on the same link.

Apply the changes:
Save the file and exit the editor. Then apply the changes by running:

sudo netplan apply

Conclusion

By following these steps, your Ubuntu system will be configured to use an IPv6 gateway outside of the assigned /48 network. This ensures proper network routing and connectivity.

Additional Resources

• Netplan Documentation
• Ubuntu Networking Configuration