auto he-ipv6
iface he-ipv6 inet6 v4tunnel
address 2001:470:xxxx::2
netmask 48
endpoint xxx.xxx.xxx.xxx
local xxx.xxx.xxx.xxx
ttl 255
gateway 2001:470:xxx::1
post-up /sbin/ip -6 route replace local 2001:470:xxx::/48 dev lo
. . .
net.ipv6.ip_nonlocal_bind = 1
net.ipv6.conf.<YOUR_MAIN_INTERFACE_NAME>.disable_ipv6 = 1
Destination unreachable: Address unreachable