Hi,
Juniper has native support for Ipv6 for Mx. If you are running Srx code base then you might have to enable is specifially.
What product / Junos are you using ? Can you see the Direct Interface populated in Inet6 table ? "show route" command would help
root@210# set security forwarding-options family inet6 mode flow-based
Refer to this Kb
http://kb.juniper.net/InfoCenter/index?page=content&id=KB25697&smlogin=true&actp=search
Regards
Rakesh
Kudos if my reply has helped