I think this introduced an issue in Train (At least Train packages for Ubuntu) when using linuxbridge.

The bridges are set to the default ageing of 300 which makes instances on vlan-based networks unable to acquire network connectivity.

brctl showmacs brq.. shows that the local VM's MAC is learned from remote and thus no packets are being forwarded to it.

``` 
brctl showmacs brq33054c52-b8 | grep 3c:1c
  2     fa:16:3e:23:3c:1c       no                24.80
  1     fe:16:3e:23:3c:1c       yes                0.00
  1     fe:16:3e:23:3c:1c       yes                0.00

```

Flipping ageing to 0 for that bridge solves the issue and the VM acquires DHCP from neutron and responds to network traffic.

``` 
brctl showmacs brq33054c52-b8 | grep 3c:1c
  1     fe:16:3e:23:3c:1c       yes                0.00
  1     fe:16:3e:23:3c:1c       yes                0.00

```

However as a side-effect it seems that packets are being duplicated for some reason..

```
64 bytes from 10.13.37.87: icmp_seq=1 ttl=64 time=0.809 ms
64 bytes from 10.13.37.87: icmp_seq=1 ttl=64 time=0.833 ms (DUP!)
64 bytes from 10.13.37.87: icmp_seq=1 ttl=64 time=0.837 ms (DUP!)
64 bytes from 10.13.37.87: icmp_seq=1 ttl=64 time=0.955 ms (DUP!)
64 bytes from 10.13.37.87: icmp_seq=1 ttl=64 time=0.965 ms (DUP!)
64 bytes from 10.13.37.87: icmp_seq=1 ttl=64 time=0.968 ms (DUP!)
```

Packages:
ii  python3-os-vif                       1.17.0-0ubuntu1~cloud0                         all          Integration library between network and compute - Python 3.x
ii  nova-common                          2:20.0.0~rc1-0ubuntu3~cloud0                   all          OpenStack Compute - common files
ii  nova-compute                         2:20.0.0~rc1-0ubuntu3~cloud0                   all          OpenStack Compute - compute node base
ii  nova-compute-kvm                     2:20.0.0~rc1-0ubuntu3~cloud0                   all          OpenStack Compute - compute node (KVM)
ii  nova-compute-libvirt                 2:20.0.0~rc1-0ubuntu3~cloud0                   all          OpenStack Compute - compute node libvirt support
ii  python3-nova                         2:20.0.0~rc1-0ubuntu3~cloud0                   all          OpenStack Compute Python 3 libraries
ii  python3-novaclient                   2:15.1.0-0ubuntu2~cloud0                       all          client library for OpenStack Compute API - 3.x
ii  neutron-common                       2:15.0.0~rc1-0ubuntu1~cloud0                   all          Neutron is a virtual network service for Openstack - common
ii  neutron-linuxbridge-agent            2:15.0.0~rc1-0ubuntu1~cloud0                   all          Neutron is a virtual network service for Openstack - linuxbridge agent
ii  python3-neutron                      2:15.0.0~rc1-0ubuntu1~cloud0                   all          Neutron is a virtual network service for Openstack - Python library
ii  python3-neutron-lib                  1.29.1-0ubuntu1~cloud0                         all          Neutron shared routines and utilities - Python 3.x
ii  python3-neutronclient                1:6.7.0-0ubuntu1                               all          client API library for Neutron - Python 3.x


Any pointers on debugging this?