Attaches an IPv6 prefix attribute:
$ipv6Prefix = "2001:1111:2222:3333::";
$ipv6PrefixLength = "64";
// Framed-IPv6-Prefix
radius_put_attr($res, 97, chr(0).chr($ipv6PrefixLength).inet_pton($ipv6Prefix));
// Delegated-IPv6-Prefix
radius_put_attr($res, 123, chr(0).chr($ipv6PrefixLength).inet_pton($ipv6Prefix));