func setupIPMasq(ipn ip.IP4Net) error {
	ipt, err := iptables.New()
	if err != nil {
		return fmt.Errorf("failed to setup IP Masquerade. iptables was not found")
	}

	err = ipt.ClearChain("nat", "FLANNEL")
	if err != nil {
		return fmt.Errorf("Failed to create/clear FLANNEL chain in NAT table: %v", err)
	}

	rules := [][]string{
		// This rule makes sure we don't NAT traffic within overlay network (e.g. coming out of docker0)
		{"FLANNEL", "-d", ipn.String(), "-j", "ACCEPT"},
		// NAT if it's not multicast traffic
		{"FLANNEL", "!", "-d", "224.0.0.0/4", "-j", "MASQUERADE"},
		// This rule will take everything coming from overlay and sent it to FLANNEL chain
		{"POSTROUTING", "-s", ipn.String(), "-j", "FLANNEL"},
	}

	for _, rule := range rules {
		log.Info("Adding iptables rule: ", strings.Join(rule, " "))
		chain := rule[0]
		args := rule[1:len(rule)]

		err = ipt.AppendUnique("nat", chain, args...)
		if err != nil {
			return fmt.Errorf("Failed to insert IP masquerade rule: %v", err)
		}
	}

	return nil
}

func rules(ipn ip.IP4Net) [][]string {
	n := ipn.String()

	return [][]string{
		// This rule makes sure we don't NAT traffic within overlay network (e.g. coming out of docker0)
		{"-s", n, "-d", n, "-j", "RETURN"},
		// NAT if it's not multicast traffic
		{"-s", n, "!", "-d", "224.0.0.0/4", "-j", "MASQUERADE"},
		// Masquerade anything headed towards flannel from the host
		{"!", "-s", n, "-d", n, "-j", "MASQUERADE"},
	}
}

func configureIface(ifname string, ipn ip.IP4Net, mtu int) error {
	iface, err := netlink.LinkByName(ifname)
	if err != nil {
		return fmt.Errorf("failed to lookup interface %v", ifname)
	}

	err = netlink.AddrAdd(iface, &netlink.Addr{ipn.ToIPNet(), ""})
	if err != nil {
		return fmt.Errorf("failed to add IP address %v to %v: %v", ipn.String(), ifname, err)
	}

	err = netlink.LinkSetMTU(iface, mtu)
	if err != nil {
		return fmt.Errorf("failed to set MTU for %v: %v", ifname, err)
	}

	err = netlink.LinkSetUp(iface)
	if err != nil {
		return fmt.Errorf("failed to set interface %v to UP state: %v", ifname, err)
	}

	// explicitly add a route since there might be a route for a subnet already
	// installed by Docker and then it won't get auto added
	err = netlink.RouteAdd(&netlink.Route{
		LinkIndex: iface.Attrs().Index,
		Scope:     netlink.SCOPE_UNIVERSE,
		Dst:       ipn.Network().ToIPNet(),
	})
	if err != nil && err != syscall.EEXIST {
		return fmt.Errorf("Failed to add route (%v -> %v): %v", ipn.Network().String(), ifname, err)
	}

	return nil
}

func (esr *etcdSubnetRegistry) updateSubnet(ctx context.Context, network string, sn ip.IP4Net, attrs *LeaseAttrs, ttl time.Duration, asof uint64) (time.Time, error) {
	key := path.Join(esr.etcdCfg.Prefix, network, "subnets", sn.StringSep(".", "-"))
	value, err := json.Marshal(attrs)
	if err != nil {
		return time.Time{}, err
	}

	resp, err := esr.client().Set(ctx, key, string(value), &etcd.SetOptions{
		PrevIndex: asof,
		TTL:       ttl,
	})
	if err != nil {
		return time.Time{}, err
	}

	ensureExpiration(resp, ttl)
	return *resp.Node.Expiration, nil
}

func configureIface(ifname string, ipn ip.IP4Net, mtu int) error {
	iface, err := net.InterfaceByName(ifname)
	if err != nil {
		return fmt.Errorf("failed to lookup interface %v", ifname)
	}

	n := ipn.ToIPNet()
	err = netlink.NetworkLinkAddIp(iface, n.IP, n)
	if err != nil {
		return fmt.Errorf("failed to add IP address %v to %v: %v", n.IP, ifname, err)
	}

	err = netlink.NetworkSetMTU(iface, mtu)
	if err != nil {
		return fmt.Errorf("failed to set MTU for %v: %v", ifname, err)
	}

	err = netlink.NetworkLinkUp(iface)
	if err != nil {
		return fmt.Errorf("failed to set interface %v to UP state: %v", ifname, err)
	}

	// explicitly add a route since there might be a route for a subnet already
	// installed by Docker and then it won't get auto added
	err = netlink.AddRoute(ipn.Network().String(), "", "", ifname)
	if err != nil && err != syscall.EEXIST {
		return fmt.Errorf("Failed to add route (%v -> %v): %v", ipn.Network().String(), ifname, err)
	}

	return nil
}

func (m *EtcdManager) allocateSubnet(config *Config, leases []Lease) (ip.IP4Net, error) {
	log.Infof("Picking subnet in range %s ... %s", config.SubnetMin, config.SubnetMax)

	var bag []ip.IP4
	sn := ip.IP4Net{IP: config.SubnetMin, PrefixLen: config.SubnetLen}

OuterLoop:
	for ; sn.IP <= config.SubnetMax && len(bag) < 100; sn = sn.Next() {
		for _, l := range leases {
			if sn.Overlaps(l.Subnet) {
				continue OuterLoop
			}
		}
		bag = append(bag, sn.IP)
	}

	if len(bag) == 0 {
		return ip.IP4Net{}, errors.New("out of subnets")
	} else {
		i := randInt(0, len(bag))
		return ip.IP4Net{IP: bag[i], PrefixLen: config.SubnetLen}, nil
	}
}

func (dev *vxlanDevice) Configure(ipn ip.IP4Net) error {
	setAddr4(dev.link, ipn.ToIPNet())

	if err := netlink.LinkSetUp(dev.link); err != nil {
		return fmt.Errorf("failed to set interface %s to UP state: %s", dev.link.Attrs().Name, err)
	}

	// explicitly add a route since there might be a route for a subnet already
	// installed by Docker and then it won't get auto added
	route := netlink.Route{
		LinkIndex: dev.link.Attrs().Index,
		Scope:     netlink.SCOPE_UNIVERSE,
		Dst:       ipn.Network().ToIPNet(),
	}
	if err := netlink.RouteAdd(&route); err != nil && err != syscall.EEXIST {
		return fmt.Errorf("failed to add route (%s -> %s): %v", ipn.Network().String(), dev.link.Attrs().Name, err)
	}

	return nil
}

func (esr *etcdSubnetRegistry) deleteSubnet(ctx context.Context, network string, sn ip.IP4Net) error {
	key := path.Join(esr.etcdCfg.Prefix, network, "subnets", sn.StringSep(".", "-"))
	_, err := esr.client().Delete(ctx, key, nil)
	return err
}

func MakeSubnetKey(sn ip.IP4Net) string {
	return sn.StringSep(".", "-")
}