Comment 30 for bug 1837252

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?