Hi Chris,
I use ruby-libvirt for Vagrant and Vagrant-kvm project.
A virNetworkUpdate method with libvirt ruby binding
is essential in order to support network configuration among multi VMs in Vagrant.
Please find an attachment that is trying to support virNetworkUpdate.
https://github.com/miurahr/ruby-libvirt/tree/virNetworkUpdate
--
Hiroshi Miura