A simple example of using iptables with an empty chain to count traffic passing through a virtual network interface on linux.
You will need to edit the vagrantfile so that it points at a box you have access to. Anything debian flavoured will do.
The provision script adds an virtual ip on eth0:0 bound to 192.168.1.6, and sets up a user iptables chain that accepts all traffic, and jump rules for source and destination packets to this interface to pass through it.
vagrant up && vagrant ssh to shell in.
You can throw some traffic at the interface by telnetting to it. Something like this will do it.
Open a new shell and run nc -l 192.168.1.6 -p 12345 to listen on that interface.
From another shell telnet 192.168.1.6 12345.
Type some jank into the second shell, you should see it coming in on the first one .
From a third shell iptables -L -v should show a packet count on the user chain.