Mostly needed to reach the outside with IPv6 using an IPv6-enabled router on your link.
# /sbin/ip -6 route add <ipv6network>/<prefixlength> via <ipv6address> ¼ [dev <device>] |
# /sbin/ip -6 route add 2000::/3 via 3ffe:ffff:0:f101::1 |
# /sbin/route -A inet6 add <ipv6network>/<prefixlength> gw ¼ <ipv6address> [dev <device>] |
A device can be needed, too, if the IPv6 address of the gateway is a link local one.
# /sbin/route -A inet6 add 2000::/3 gw 3ffe:ffff:0:f101::1 |