Open Stack

Hello,
        I am trying to implement the Mixed Flat and Private Network topology with Neutron, where a VM gets 2 NICs, one to private network and other to public shared network. My physical router is acting as a gateway for public shared network (e.g. 192.168.4.1/24). When I boot up my instance (ubuntu or cirrus), i do get ip (via dhcp) on my both public (192.168.4.10) and private NICs (192.168.1.10), I can ping my private network's gateway (192.168.1.1), but can't ping my public network gateway (192.168.4.1on physical router). 
I am using OVS Gre plugin with neutron. Is there any specific knobs that I can verify. I did tcpdump and looks like packets are getting lost when transitioning from br-int to br-ex on controller/network node.
     Any help??

regards,
Ari