[libvirt] Network definition questions

If an IPv4 address is *not* specified, then the IPv4 network is isolated and, by default, internal (internal to the specific interface) IPv4 routing is enabled.. If an IPv6 address is *not* specified, then the IPv6 network is isolated and, by default, internal IPv6 routing is disabled but can be enabled if ipv6='yes' is specified on <network>. If an IPv6 address is specified, then it is routed. If an IPv4 address is specified, then it can be Network-Address-Translated or routed. Not having a <forward> explicitly specified does not mean that a route is not established. Do I understand thing correctly? Gene