about 'ivec' paramenter

Dear Pals
    It's question about the 'ivec' parameter!!
    For OpenSSL BF_cbc_encrypt() function, there is a 'ivec' parameter to
assign the initialization vector for the crypto engine. But in 'ipsecadm'
command in OpenBSD, I can't find out the relative parameters to be assigned.
    Can anyone give some comments or explanation for me how the IV assign and
process in OpenBSD  from user view?
    Thanks !!

Best Regards
/Tony