Comment 6 for bug 1564395

Out of completeness I went back to:

root@maas19-node2:/home/ubuntu# cat /var/lib/lxd/containers/juju-machine-0-lxd-1/rootfs/etc/network/interfaces

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet manual
  dns-nameservers 10.17.20.200
  pre-up ip address add 10.17.20.214/24 dev eth0 || true
  up ip route replace 10.17.20.0/24 dev eth0 || true
  down ip route del 10.17.20.0/24 dev eth0 || true
  post-down address del 10.17.20.214/24 dev eth0 || true
  up ip route replace default via 10.17.20.1 || true
  down ip route del default via 10.17.20.1 || true

auto eth1
iface eth1 inet manual
  pre-up ip address add 192.168.10.103/24 dev eth1 || true
  up ip route replace 192.168.10.0/24 dev eth1 || true
  down ip route del 192.168.10.0/24 dev eth1 || true
  post-down address del 192.168.10.103/24 dev eth1 || true

auto eth2
iface eth2 inet manual
  pre-up ip address add 192.168.11.103/24 dev eth2 || true
  up ip route replace 192.168.11.0/24 dev eth2 || true
  down ip route del 192.168.11.0/24 dev eth2 || true
  post-down address del 192.168.11.103/24 dev eth2 || true

auto eth3
iface eth3 inet manual
  pre-up ip address add 192.168.12.103/24 dev eth3 || true
  up ip route replace 192.168.12.0/24 dev eth3 || true
  down ip route del 192.168.12.0/24 dev eth3 || true
  post-down address del 192.168.12.103/24 dev eth3 || true

auto eth4
iface eth4 inet manual
  pre-up ip address add 192.168.16.101/21 dev eth4 || true
  up ip route replace 192.168.16.0/21 dev eth4 || true
  down ip route del 192.168.16.0/21 dev eth4 || true
  post-down address del 192.168.16.101/21 dev eth4 || true

auto eth5
iface eth5 inet manual
  pre-up ip address add 192.168.24.101/21 dev eth5 || true
  up ip route replace 192.168.24.0/21 dev eth5 || true
  down ip route del 192.168.24.0/21 dev eth5 || true
  post-down address del 192.168.24.101/21 dev eth5 || true

auto eth6
iface eth6 inet manual
  pre-up ip address add 192.168.32.101/21 dev eth6 || true
  up ip route replace 192.168.32.0/21 dev eth6 || true
  down ip route del 192.168.32.0/21 dev eth6 || true
  post-down address del 192.168.32.101/21 dev eth6 || true

root@maas19-node2:/home/ubuntu# exit
ubuntu@maas19-node2:~$ logout
Connection to 10.17.20.213 closed.
aim@spicy:~/juju ((0798f54...)) (local.maas)
$ git log
commit 0798f5452273f653c561fb6d8f8543aa85ea7f5a
Merge: 965f56c 68fdac3
Author: Juju bot <email address hidden>
Date: Sat Mar 19 17:36:04 2016 +0000

    Merge pull request #4802 from dimitern/m-s-m-n-c-w-m-multi-nic-lxd

    Enable multi-NIC LXD containers on MAAS

    This is essentially https://github.com/juju/juju/pull/4789 with an minor
    fix for cloudconfig/containerinit tests. Enables multi-NIC LXD container
    provisioning on MAAS, using the same approach previously tested with
    LXC.

    Live tested on MAAS 1.9 with a mediawiki bundle deployment including
    placement to both LXC and LXD containers: http://paste.ubuntu.com/15426062/
    on both trusty and xenial.

    (Review request: http://reviews.vapour.ws/r/4244/)

and added a container to see what its /e/n/i would look like (which looks OK)

root@maas19-node2:/home/ubuntu# cat /var/lib/lxd/containers/juju-machine-0-lxd-1/rootfs/etc/network/interfaces

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet manual
  dns-nameservers 10.17.20.200
  pre-up ip address add 10.17.20.214/24 dev eth0 || true
  up ip route replace 10.17.20.0/24 dev eth0 || true
  down ip route del 10.17.20.0/24 dev eth0 || true
  post-down address del 10.17.20.214/24 dev eth0 || true
  up ip route replace default via 10.17.20.1 || true
  down ip route del default via 10.17.20.1 || true

auto eth1
iface eth1 inet manual
  pre-up ip address add 192.168.10.103/24 dev eth1 || true
  up ip route replace 192.168.10.0/24 dev eth1 || true
  down ip route del 192.168.10.0/24 dev eth1 || true
  post-down address del 192.168.10.103/24 dev eth1 || true

auto eth2
iface eth2 inet manual
  pre-up ip address add 192.168.11.103/24 dev eth2 || true
  up ip route replace 192.168.11.0/24 dev eth2 || true
  down ip route del 192.168.11.0/24 dev eth2 || true
  post-down address del 192.168.11.103/24 dev eth2 || true

auto eth3
iface eth3 inet manual
  pre-up ip address add 192.168.12.103/24 dev eth3 || true
  up ip route replace 192.168.12.0/24 dev eth3 || true
  down ip route del 192.168.12.0/24 dev eth3 || true
  post-down address del 192.168.12.103/24 dev eth3 || true

auto eth4
iface eth4 inet manual
  pre-up ip address add 192.168.16.101/21 dev eth4 || true
  up ip route replace 192.168.16.0/21 dev eth4 || true
  down ip route del 192.168.16.0/21 dev eth4 || true
  post-down address del 192.168.16.101/21 dev eth4 || true

auto eth5
iface eth5 inet manual
  pre-up ip address add 192.168.24.101/21 dev eth5 || true
  up ip route replace 192.168.24.0/21 dev eth5 || true
  down ip route del 192.168.24.0/21 dev eth5 || true
  post-down address del 192.168.24.101/21 dev eth5 || true

auto eth6
iface eth6 inet manual
  pre-up ip address add 192.168.32.101/21 dev eth6 || true
  up ip route replace 192.168.32.0/21 dev eth6 || true
  down ip route del 192.168.32.0/21 dev eth6 || true
  post-down address del 192.168.32.101/21 dev eth6 || true
root@maas19-node2:/home/ubuntu# cat /var/lib/lxd/containers/juju-machine-0-lxd-1/rootfs/etc/network/interfaces

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet manual
  dns-nameservers 10.17.20.200
  pre-up ip address add 10.17.20.214/24 dev eth0 || true
  up ip route replace 10.17.20.0/24 dev eth0 || true
  down ip route del 10.17.20.0/24 dev eth0 || true
  post-down address del 10.17.20.214/24 dev eth0 || true
  up ip route replace default via 10.17.20.1 || true
  down ip route del default via 10.17.20.1 || true

auto eth1
iface eth1 inet manual
  pre-up ip address add 192.168.10.103/24 dev eth1 || true
  up ip route replace 192.168.10.0/24 dev eth1 || true
  down ip route del 192.168.10.0/24 dev eth1 || true
  post-down address del 192.168.10.103/24 dev eth1 || true

auto eth2
iface eth2 inet manual
  pre-up ip address add 192.168.11.103/24 dev eth2 || true
  up ip route replace 192.168.11.0/24 dev eth2 || true
  down ip route del 192.168.11.0/24 dev eth2 || true
  post-down address del 192.168.11.103/24 dev eth2 || true

auto eth3
iface eth3 inet manual
  pre-up ip address add 192.168.12.103/24 dev eth3 || true
  up ip route replace 192.168.12.0/24 dev eth3 || true
  down ip route del 192.168.12.0/24 dev eth3 || true
  post-down address del 192.168.12.103/24 dev eth3 || true

auto eth4
iface eth4 inet manual
  pre-up ip address add 192.168.16.101/21 dev eth4 || true
  up ip route replace 192.168.16.0/21 dev eth4 || true
  down ip route del 192.168.16.0/21 dev eth4 || true
  post-down address del 192.168.16.101/21 dev eth4 || true

auto eth5
iface eth5 inet manual
  pre-up ip address add 192.168.24.101/21 dev eth5 || true
  up ip route replace 192.168.24.0/21 dev eth5 || true
  down ip route del 192.168.24.0/21 dev eth5 || true
  post-down address del 192.168.24.101/21 dev eth5 || true

auto eth6
iface eth6 inet manual
  pre-up ip address add 192.168.32.101/21 dev eth6 || true
  up ip route replace 192.168.32.0/21 dev eth6 || true
  down ip route del 192.168.32.0/21 dev eth6 || true
  post-down address del 192.168.32.101/21 dev eth6 || true