Eu tentei uma pesquisa por freebsd ip tools ipv6
. Eu encontrei instruções no link .
method 1) completely static configuration like IPv4
Linklocal prefix (fe80:....) is automatically generated, so you
don't have to configure it.
-------/etc/rc.conf---------
ipv6_network_interfaces="fxp0"
ipv6_ifconfig_fxp0="3ffe:501:ffff:2::1 prefixlen 64"
ipv6_ifconfig_fxp0_alias0="2001:ffff:0:2::2 prefixlen 64"
ipv6_defaultrouter="fe80::1%fxp0"
----------------------------