s.Spec.IPFamilies = nil
			},
			numErrs: 0,
		}, {
			name: "valid, service with valid ipFamilies (v4)",
			tweakSvc: func(s *core.Service) {
				s.Spec.IPFamilies = []core.IPFamily{core.IPv4Protocol}
			},
			numErrs: 0,
		}, {
			name: "valid, service with valid ipFamilies (v6)",
			tweakSvc: func(s *core.Service) {
				s.Spec.IPFamilies = []core.IPFamily{core.IPv6Protocol}

					IPFamilies: []v1.IPFamily{v1.IPv6Protocol}, // <- set by a api-server defaulting logic
				},
			},
			expectedEndpointFamily: ipv6,
		},
		{
			name:       "v6 legacy headless service, in a dual stack cluster  (connected to a old api-server)",
			ipFamilies: ipv4ipv6,
			service: v1.Service{
				Spec: v1.ServiceSpec{
					ClusterIP: v1.ClusterIPNone, // <- families are not set by api-server

  //
  // This field may hold a maximum of two entries (dual-stack families, in
  // either order).  These families must correspond to the values of the
  // clusterIPs field, if specified. Both clusterIPs and ipFamilies are
  // governed by the ipFamilyPolicy field.
  // +listType=atomic
  // +optional
  repeated string ipFamilies = 19;

  // IPFamilyPolicy represents the dual-stack-ness requested or required by

	"ipFamilyPolicy":                "IPFamilyPolicy represents the dual-stack-ness requested or required by this Service. If there...

		}
	}

	// match clusterIPs to their families, if they were provided
	if !isHeadlessService(service) && len(service.Spec.ClusterIPs) > 0 && len(service.Spec.IPFamilies) > 0 {
		for i, ip := range service.Spec.ClusterIPs {
			if i > (len(service.Spec.IPFamilies) - 1) {
				break // no more families to check
			}

			// 4=>6
			if service.Spec.IPFamilies[i] == core.IPv4Protocol && netutils.IsIPv6String(ip) {

have been born into the cause; innumerable young people have married into it; innumerable old people have died out of it. Scores of persons have deliriously found themselves made parties in Jarndyce and Jarndyce, without knowing how or why; whole families have inherited legendary hatreds with the suit. The little plaintiff or defendant, who was promised a new rocking-horse when Jarndyce and Jarndyce should be settled, has grown up, possessed himself of a real horse, and trotted away into the other...

  //
  // This field may hold a maximum of two entries (dual-stack families, in
  // either order).  These families must correspond to the values of the
  // clusterIPs field, if specified. Both clusterIPs and ipFamilies are
  // governed by the ipFamilyPolicy field.
  // +listType=atomic
  // +optional
  repeated string ipFamilies = 19;

  // IPFamilyPolicy represents the dual-stack-ness requested or required by

		return ip.addr.xor(p.ip.addr).and(mask6(p.Bits())).isZero()
	}
}

// Overlaps reports whether p and o contain any IP addresses in common.
//
// If p and o are of different address families or either have a zero
// IP, it reports false. Like the Contains method, a prefix with an
// IPv4-mapped IPv6 address is still treated as an IPv6 mask.
func (p Prefix) Overlaps(o Prefix) bool {

		a, b Prefix
		want bool
	}{
		{Prefix{}, pfx("1.2.0.0/16"), false},    // first zero
		{pfx("1.2.0.0/16"), Prefix{}, false},    // second zero
		{pfx("::0/3"), pfx("0.0.0.0/3"), false}, // different families

		{pfx("1.2.0.0/16"), pfx("1.2.0.0/16"), true}, // equal

		{pfx("1.2.0.0/16"), pfx("1.2.3.0/24"), true},
		{pfx("1.2.3.0/24"), pfx("1.2.0.0/16"), true},

	// This field may hold a maximum of two entries (dual-stack families, in
	// either order).  These families must correspond to the values of the
	// clusterIPs field, if specified. Both clusterIPs and ipFamilies are
	// governed by the ipFamilyPolicy field.
	// +listType=atomic
	// +optional
	IPFamilies []IPFamily `json:"ipFamilies,omitempty" protobuf:"bytes,19,opt,name=ipFamilies,casttype=IPFamily"`