neutron openvswitch br-int can't reach external network br-ex through patch - networking

Question

I installed openstack liberty with 2 node configuration (1 controller, 1 compute), each one having 1 public nic and 1 private nic, and following this scenario with dvr: http://docs.openstack.org/networking-guide/scenario_dvr_ovs.html
In the controller node I created br-ex which has the eth0' IP (this is the public nic), and installed l3-agent (dvr_snat mode) ovs-agent dhcp-agent and services.
Using the admin account I created the ext-net and attached my subnet to it.
Using the demo tenant, I created then a demo-net, a demo-subnet and a demo-router, then I set the gateway neutron router-gateway-set demo-net ext-net
So my ovs-vsctl show looks as the following
Bridge br-int
fail_mode: secure
Port "sg-ef30b544-a4"
tag: 4095
Interface "sg-ef30b544-a4"
type: internal
Port "qr-a4b8653c-78"
tag: 4095
Interface "qr-a4b8653c-78"
type: internal
Port "qg-d33db11d-60"
tag: 1
Interface "qg-d33db11d-60"
type: internal
Port br-int
Interface br-int
type: internal
Port "tap9f36ccde-1e"
tag: 4095
Interface "tap9f36ccde-1e"
type: internal
Port int-br-ex
Interface int-br-ex
type: patch
options: {peer=phy-br-ex}
Bridge br-ex
Port "eth0"
Interface "eth0"
Port br-ex
Interface br-ex
type: internal
Port phy-br-ex
Interface phy-br-ex
type: patch
options: {peer=int-br-ex}
Bridge br-tun
Port br-tun
Interface br-tun
type: internal
ovs_version: "2.4.0"
and the network namespaces
root#controller:~# ip netns
qdhcp-3e662de0-9a85-4d7d-bb85-b9d4568ceaec
snat-f3f6213c-384c-4ec5-914c-e98aba89936f
qrouter-f3f6213c-384c-4ec5-914c-e98aba89936f
My problem is that l3-agent fails to setup the snat network, because it seems that the network is unreachable.
ERROR neutron.agent.l3.agent Command: ['sudo', '/usr/bin/neutron-rootwrap', '/etc/neutron/rootwrap.conf', 'ip', 'netns', 'exec', 'snat-f3f6213c-384c-4ec5-914c-e98aba89936f', 'ip', '-4', 'route', 'replace', 'default', 'via', '149.XXX.YYY.ZZZ', 'dev', 'qg-d33db11d-60']
ERROR neutron.agent.l3.agent Exit code: 2
ERROR neutron.agent.l3.agent Stdin:
ERROR neutron.agent.l3.agent Stdout:
ERROR neutron.agent.l3.agent Stderr: RTNETLINK answers: Network is unreachable
ping -I br-ex 8.8.8.8 works.
ping -I br-int 8.8.8.8 says network unreachable.
As you can see there is a patch between br-int and br-ex, so it should work, but it doesn't.