gistfile1.txt

guest:

auto lo
iface lo inet loopback

iface eth0 inet 6 static
   address 2a01:4f8:160:3122::1:1
   netmask 64
   gateway 2a01:4f8:160:3122::3

host:

### Hetzner Online AG - installimage
# Loopback device:
auto lo
iface lo inet loopback

# device: eth0
auto  eth0
iface eth0 inet static
  address   176.9.148.50
  broadcast 176.9.148.63
  netmask   255.255.255.224
  gateway   176.9.148.33

# default route to access subnet
up route add -net 176.9.148.32 netmask 255.255.255.224 gw 176.9.148.33 eth0

auto virbr0
iface virbr0 inet static
   address 176.9.148.50
   netmask 255.255.255.255
   bridge_stp off
   bridge_fd 0
   pre-up brctl addbr virbr0
   up ip -6 neigh add proxy 2a01:4f8:160:3122::2 dev virbr0
   post-down  brctl delbr virbr0

iface virbr0 inet6 static
   address 2a01:4f8:160:3122::3
   netmask 64
   up ip -6 neigh add proxy 2a01:4f8:160:3122::1:1 dev eth0