func electBridgeIPv4(config *NetworkConfiguration) (*net.IPNet, error) {
	// Use the requested IPv4 CIDR when available.
	if config.AddressIPv4 != nil {
		return config.AddressIPv4, nil
	}

	// We don't check for an error here, because we don't really care if we
	// can't read /etc/resolv.conf. So instead we skip the append if resolvConf
	// is nil. It either doesn't exist, or we can't read it for some reason.
	nameservers := []string{}
	if resolvConf, _ := readResolvConf(); resolvConf != nil {
		nameservers = append(nameservers, getNameserversAsCIDR(resolvConf)...)
	}

	// Try to automatically elect appropriate bridge IPv4 settings.
	for _, n := range bridgeNetworks {
		if err := netutils.CheckNameserverOverlaps(nameservers, n); err == nil {
			if err := netutils.CheckRouteOverlaps(n); err == nil {
				return n, nil
			}
		}
	}

	return nil, IPv4AddrRangeError(config.BridgeName)
}

// FindAvailableNetwork returns a network from the passed list which does not
// overlap with existing interfaces in the system
func FindAvailableNetwork(list []*net.IPNet) (*net.IPNet, error) {
	// We don't check for an error here, because we don't really care if we
	// can't read /etc/resolv.conf. So instead we skip the append if resolvConf
	// is nil. It either doesn't exist, or we can't read it for some reason.
	var nameservers []string
	if rc, err := resolvconf.Get(); err == nil {
		nameservers = resolvconf.GetNameserversAsCIDR(rc.Content)
	}
	for _, nw := range list {
		if err := netutils.CheckNameserverOverlaps(nameservers, nw); err == nil {
			if err := netutils.CheckRouteOverlaps(nw); err == nil {
				return nw, nil
			}
		}
	}
	return nil, fmt.Errorf("no available network")
}

func isOverlap(nw *net.IPNet) bool {
	var nameservers []string

	if rc, err := resolvconf.Get(); err == nil {
		nameservers = resolvconf.GetNameserversAsCIDR(rc.Content)
	}

	if err := netutils.CheckNameserverOverlaps(nameservers, nw); err != nil {
		return true
	}

	if err := netutils.CheckRouteOverlaps(nw); err != nil {
		return true
	}

	return false
}

func checkOverlap(nw *net.IPNet) error {
	var nameservers []string

	if rc, err := resolvconf.Get(); err == nil {
		nameservers = resolvconf.GetNameserversAsCIDR(rc.Content)
	}

	if err := netutils.CheckNameserverOverlaps(nameservers, nw); err != nil {
		return fmt.Errorf("overlay subnet %s failed check with nameserver: %v: %v", nw.String(), nameservers, err)
	}

	if err := netutils.CheckRouteOverlaps(nw); err != nil {
		return fmt.Errorf("overlay subnet %s failed check with host route table: %v", nw.String(), err)
	}

	return nil
}