Most of the modern versions of FreeBSD have IPsec support in their base source. So you will need to include the
<option>IPSEC
</option> option in your kernel config and, after kernel rebuild and reinstall, configure IPsec connections using
<citerefentry><refentrytitle>setkey
</refentrytitle><manvolnum>8
</manvolnum></citerefentry> command.