It seems to me you can control traffic using the MPLS router. We have an MPLS line that connects offices A (us), B and C. It hits a Sonic firewall on A (us) before it gets into our LAN.
Office "B" is trying to hit our local LAN and it works fine.
Office "C" wants to hit our LAN and then use our internet gateway to get out to the net. This doesn't seem to be working when they try to reach the net thru us though. Is there a better way to accomplish this?
SONICWALL SONIC WALL
Office B-----MPLS------>Office A (us)---------OUR Internet---(office C is trying to go out thru us)
| SONIC WALL