How to set up IPv6 with netplan on Ubuntu 18.04?

I purchased a dedicated server installed with Ubuntu 18.04 which was given an IPv6 Block.

I used the guide How to set up IPv6 on Ubuntu 16.04 before. Since Ubuntu 18.04 uses netplan instead of /etc/network/interfaces, the above link does not work anymore.

Yesterday, I set up /etc/netplan/01-netcfg.yaml as following:

network:                                                                       
version: 2
renderer: networkd
ethernets:
  eno1:
    dhcp4: yes
    dhcp6: no
    addresses: ['2001:bc8:xxx:100::/56']

Things worked pretty well, but today I can no longer ping any IPv6 addresses. Tried in many ways but so far I can have no good result.

I want to know the exact way of implementing IPv6 under this circumstance, how should I do?

I also have a Dedibox server from Online.net.

After searching the web I find this on twitter

Try the following :

network:                                                                       
version: 2
renderer: networkd
ethernets:
  eno1:
    dhcp4: yes
    dhcp6: no
    addresses:
    - 2001:bc8:xxx:100::/56

This worked for me and now I'm able to ping6 !