Hi Francisco,
The following link should help determine when you should use the "qos pre-classify" & the placement of the service-policy command.
Apply the policy to the tunnel interface without qos-preclassify when you want to classify packets based on the pre-tunnel header.
Apply the policy to the physical interface without qos-preclassify when you want to classify packets based on the post-tunnel header. In addition, apply the policy to the physical interface when you want to shape or police all traffic belonging to a tunnel, and the physical interface supports several tunnels.
Apply the policy to a physical interface and enable qos-preclassify on a tunnel interface when you want to classify packets based on the pre-tunnel header.
http://www.cisco.com/en/US/tech/tk543/tk545/technologies_tech_note09186a008017405e.shtml
Tim
