Sorry, just realized there is a VMmanager app too (free version seem to only have support for Debian 7 though.) I am using the Virtual Machine Manager GUI (virt-manager.)

-----Original Message-----
From: Laine Stump <laine@laine.org>
To: libvirt-users@redhat.com
Cc: shorawitz@gmail.com
Subject: Re: [libvirt-users] Isolated networks && test lab
Date: Thu, 27 Aug 2015 19:26:03 -0400

On 08/27/2015 07:13 PM, Spanky Horawitz wrote:

Thank you! I am still playing with KVM, and will more than likely setup my lab as you suggest in order to isolate the guests from the host. Not sure if I can create an isolated network from VM Manager.

I just tried it and yes it is possible. On the 2nd screen where it asks for IPv4 info, just uncheck the "Enable IPv4" checkbox, then on screen 4, clear out the "DNS Domain Name" at the bottom of the page. This will give you a virtual network with a bridge created by libvirt, but no IP address on the bridge itself, so no traffic will be able to go to/from the host from that bridge. The only other bit you'll need to do is setup the dhcp server on the router guest.