Issue in external network communication when multiple networks are configured

Issue Occurrence: When two internal networks are created and with one of the internal network communication is established with the external network.

Set-up details: ODL Cluster running carbon distro, 1 control and 2 compute nodes with ocata(Packstack)

Reproducing the Issue:

1. Create Internal Network and Subnet (net1)
2. Create a VM for this network.(vm1)
3. Create external network and subnet (externl_net1)
4. Create a router and set gateway to the external network and add a interface to the internal network (net1)
5. Create a floating ip and associate it to vm1.
6. Check for the communication from vm1 to external host - SUCCESS
7. Now create another internal network and subnet(net2)
8. Create a VM for this network (vm2)
9. Create a router and add both the network's interface.
10. In the vm1 add the route gateway for the net2 and check for communication from vm1 to external host - FAIL

This issue can be reproduced even when we create both the internal networks one after another and then the external network. Then create one router for both the internal networks and another router for the internal and external network.
Here when we try to establish the communication between the internal and external host it fails .