IPv6 network configuration /etc/network/interfaces

interfaces

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet dhcp

# Primary network interface ipv6 settings
# This isn't needed if you are only connecting out with this machine.
# Later I am providing IPv6 connectivity to my whole network.
iface eth0 inet6 static
address 2001:470:d51f:f35::1
netmask 64

# ipv6 tunnel
auto he-ipv6
iface he-ipv6 inet6 v4tunnel
endpoint 
209.51.191.5

address 2001:470:d51e:f35::1/64
netmask 64
up ip -6 route add default dev he-ipv6
down ip -6 route del default dev he-ipv6