Router interfaces constructed with pre-created ports fails L3 in Datapath when such router is put into BGPVPN

When the router interfaces are added using pre-constructed neutron ports (with subnet gateway ips of course), and then when we associate such router to a L3 BGPVPN, L3 forwarding fails in datapath between VMs on the arms of such router.

Steps to create the problem:

1. Create network 1

2. Create a subnet1 on network1.

3. Boot VM1 on network 1

4. Create network 2

5. Create a subnet2 on network2.

6. Boot VM2 on network 2

7. Create a Router

8. Create a port using neutron-port-create
with name as say "port-router-net1-interface" and fixed-ip as subnet gateway ip of subnet1.

9. Create a port using neutron-port-create
with name as say "port-router-net2-interface" and fixed-ip as subnet gateway ip of subnet2.

10. Attach "port-router-net1-interface' to the router using
neutron router-interface-add Router port=port-router-net1-interface

11. Attach "port-router-net2-interface" to the router using
neutron router-interface-add Router port=port-router-net2-interface

12. Now make sure VM1 pings VM2. It may fail (or) succeed

13. Create a L3 BGPVPN.
neutron bgpvpn-create --route-targets 40:4 --import-targets 40:1 --route-distinguishers '400:1' --tenant_id $(keystone tenant-list | grep '\sadmin' | awk '

{print $2}') --name myBgpVpn1

14. Associate the router to this myBgpVpn1.
neutron bgpvpn-net-assoc-create myBgpVpn1 --network $(neutron router-list |grep '\sRouter' |awk '{print $2}

')

15. Now again ping from VM1 to VM2 and it FAILS.