Gfilui

I recently installed a new VM using Ubuntu 16.04, but I am unable to copy the post-up and pre-down rules that I use in my 14.04 install.

Can you please advise what to use? I've added a few notes to indicate what each of my edited out ips are

Example of the 14.04 config:

# The primary network interface
auto eth0
iface eth0 inet static
 address x.x.x.109 #vm ip
 netmask 255.255.255.255
 broadcast x.x.x.109 #vm ip
 post-up route add x.x.x.254 dev eth0 #root machine gateway
 post-up route add default gw x.x.x.254 #root machine gateway
 pre-down route del x.x.x.254 dev eth0 #root machine gateway
 pre-down route del default gw x.x.x.254 #root machine gateway
 dns-nameservers 213.186.33.99 8.8.8.8

Try with up and down instead of post-up and pre-down.

Example :

auto eth0
iface eth0 inet static
 address 192.168.1.1
 netmask 255.255.255.0
 up route add -net 192.168.2.0 netmask 255.255.255.0 gw 192.168.1.1

Or, but I didn't test it, you can write a bash script and put it in the folder /etc/network/if-up.d/ and /etc/network/if-down.d/ (you can use the variable $IFACE to know which interface is getting a connection).

In /etc/network/if-up.d/some-script:

#!/bin/bash

if [[ $IFACE == "eth0" ]]; then
 ip route add x.x.x.0/24 via x.x.x.254 dev $IFACE
fi

Hope this help.