How to configure IPv6

Edit the Netplan configuration

Open the YAML file in /etc/netplan/ (the filename varies by image, for example 01-netcfg.yaml or 50-cloud-init.yaml):

sudo nano /etc/netplan/01-netcfg.yaml

Add the IPv6 address to the addresses list alongside your IPv4 address, and route the default gateway for each address family. Recent Netplan releases no longer use the gateway4 / gateway6 keys, use routes instead:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp1s0:
      accept-ra: false
      addresses:
        - 192.168.1.2/24
        - 2001:db8:112::2/64
      routes:
        - to: default
          via: 192.168.1.1
        - to: default
          via: 2001:db8:112::1
      nameservers:
        addresses:
          - 9.9.9.9
          - 1.1.1.1

The example uses 2001:db8:112::/64, a prefix reserved for documentation, so it will never be your real subnet. Replace it with the values supplied for your server. The two resolvers shown are well-known public ones, included so the config is complete and testable. Use a public resolver you trust, or leave DNS on the default your server already provides. See Worldstream DNS servers.

Apply the configuration

sudo netplan try

netplan try applies the configuration, then asks you to confirm it. If you do not confirm within the timeout, it rolls back automatically, so a broken file cannot leave you locked out of your own server. Use sudo netplan apply only when you are certain the file is correct.

Find the connection name

nmcli connection show

Set the IPv6 address and gateway

sudo nmcli connection modify "System enp1s0" ipv6.method manual ipv6.addresses 2001:db8:112::2/64 ipv6.gateway 2001:db8:112::1
sudo nmcli connection up "System enp1s0"

Ping an IPv6 address

ping -6 2001:4860:4860::8888

Some older systems still use the separate ping6 command instead of the -6 flag on ping; use whichever your distribution provides.