IPv6 IPsec tunnel configuration

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Dear all:

I want to set up the gif tunnel for IPv6 IPsec as the Freebsd Handbook 
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/ipsec.html
"VPN over IPsec" suggested for IPv4. However, I could not configure the 
local IP address via
"ifconfig gif0 inet6 <local private IPv6 address> <remote private IPv6 
address>", ifconfig will complain the parameters are invalid!

Is there any other way to configure the IPv6 IPsec tunnel?

Thanks.

BR,

Yi-Wen