Ytdyklly

I'm renting a dedicated server at Hetzner and installed Ubuntu server 18.04 LTS on it.
I've got two public IPv4 addresses named x.x.x.x and y.y.y.y and one IPv6 /64 block for connecting my private networks to the internet. I use NAT for IPv4.

My network is configured using Netplan as follows:

network:    

  version: 2

  renderer: networkd

  ethernets:

    eth0:

      addresses:

        - x.x.x.x/32

        - y.y.y.y/32

        - a.a.a.a::2/64

      routes:

        - on-link: true

          to: 0.0.0.0/0

          via: z.z.z.z

      gateway6: fe80::1

      nameservers:

        addresses:

          - 1.1.1.1

          - 1.0.0.1

          - 2606:4700:4700::1111

          - 2606:4700:4700::1001

  bridges:

    xenbr0:

      interfaces: 

      addresses:

        - 192.168.0.1/24

        - a.a.a.a::3/64

      parameters:

        forward-delay: 0

        stp: false

    xenbr1:

      interfaces: 

      addresses:

        - 192.168.1.1/24

        - a.a.a.a::4/64

      parameters:

        forward-delay: 0

        stp: false

The installation and configuration of XEN:

sudo apt-get install xen-hypervisor-amd64 xen-tools

sudo reboot

sudo vim /etc/default/grub

   GRUB_CMDLINE_XEN_DEFAULT="dom0_mem=min:1024M,max:1024M dom0_max_vcpus=2 dom0_vcpus_pin"

sudo vim /etc/xen/xl.conf

   autoballoon=0

sudo update-grub

sudo reboot

VM's should be accessible to and from the Internet using IP forwarding and NAT.

sudo vim /etc/sysctl.conf

   net.ipv4.ip_forward=1

sudo sysctl -p /etc/sysctl.conf

sudo apt-get install iptables-persistent

The NAT part:

sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

Forward HTTP and HTTPS requests to our VM2 server:

sudo iptables -A PREROUTING -t nat -p tcp -i eth0 -d x.x.x.x --dport 80 -j DNAT --to 192.168.0.11:80

sudo iptables -A PREROUTING -t nat -p tcp -i eth0 -d x.x.x.x --dport 443 -j DNAT --to 192.168.0.11:443

We don't want any traffic between 192.168.0.x <-> 192.168.0.y so we drop all data packages with some simple rules. This Blocks communication between the bridges:

sudo iptables -P FORWARD DROP

sudo iptables -A FORWARD -i eth0 -o xenbr0 -j ACCEPT

sudo iptables -A FORWARD -i xenbr0 -o eth0 -s 192.168.0.0/24 -j ACCEPT

sudo iptables -A FORWARD -i eth0 -o xenbr1 -j ACCEPT

sudo iptables -A FORWARD -i xenbr1 -o eth0 -s 192.168.1.0/24 -j ACCEPT

The IPv4 part works perfectly but the IPv6 doesn't. I've assigned an IPv6 address manually to my VM's.When logged in to VM1 i can ping xenbr0 at address ::3 and VM2 at address ::11 but can't ping eth0 at address ::2.
It's like the bridge prevents the IPv6 traffic from leaving the network but can't figure out why.