libvirt users - Dec 2018 - connecting two vm in a network

Greetings,

my router is running under a vm, I want to start another vm on that host and
have to connected to the router vm in the same manner the host connects to the
vm router.
looking at the docs, I think that guest private network is what I need. thing
is, from what I see, I need to define an ip and such. that's what the router
suppose to provide so I'm not sure what exactly I need to configure and how.

what is the correct config to achieve what I need?

Thanks,

Dagg.