Multiple IPv6 addresses per interface Debian / Ubuntu

To set multiple IPv6 addresses on one interface in Linux, you can use the tool ip.

ip addr add first_ipv6_address dev eth1
ip addr add second_ipv6_address dev eth1

When you like to set this on the system boot, you must do this in /etc/network/interfaces

auto eth0
iface eth0 inet6 static
address first_ipv6_address Adress
netmask 128
gateway ipv6_gateway
up ip addr add second_ipv6_address/128 dev eth1
down ip addr del second_ipv6_address/128 dev eth1