@@ -380,7 +380,7 @@ func TestSRVServiceQuery(t *testing.T) {

 	sr := svcInfo{

 		svcMap:     make(map[string][]net.IP),

 		svcIPv6Map: make(map[string][]net.IP),

-		ipMap:      make(map[string]string),

+		ipMap:      make(map[string]*ipInfo),

 		service:    make(map[string][]servicePorts),

 	}

 	// backing container for the service

@@ -80,10 +80,18 @@ type NetworkInfo interface {

 // When the function returns true, the walk will stop.

 type EndpointWalker func(ep Endpoint) bool

+// ipInfo is the reverse mapping from IP to service name to serve the PTR query.

+// extResolver is set if an externl server resolves a service name to this IP.

+// Its an indication to defer PTR queries also to that external server.

+type ipInfo struct {

+	name        string

+	extResolver bool

+}

+

 type svcInfo struct {

 	svcMap     map[string][]net.IP

 	svcIPv6Map map[string][]net.IP

-	ipMap      map[string]string

+	ipMap      map[string]*ipInfo

 	service    map[string][]servicePorts

 }

@@ -1070,10 +1078,12 @@ func (n *network) updateSvcRecord(ep *endpoint, localEps []*endpoint, isAdd bool

 	}

 }

-func addIPToName(ipMap map[string]string, name string, ip net.IP) {

+func addIPToName(ipMap map[string]*ipInfo, name string, ip net.IP) {

 	reverseIP := netutils.ReverseIP(ip.String())

 	if _, ok := ipMap[reverseIP]; !ok {

-		ipMap[reverseIP] = name

+		ipMap[reverseIP] = &ipInfo{

+			name: name,

+		}

 	}

 }

@@ -1117,7 +1127,7 @@ func (n *network) addSvcRecords(name string, epIP net.IP, epIPv6 net.IP, ipMapUp

 		sr = svcInfo{

 			svcMap:     make(map[string][]net.IP),

 			svcIPv6Map: make(map[string][]net.IP),

-			ipMap:      make(map[string]string),

+			ipMap:      make(map[string]*ipInfo),

 		}

 		c.svcRecords[n.ID()] = sr

 	}

@@ -1612,8 +1622,8 @@ func (n *network) ResolveName(req string, ipType int) ([]net.IP, bool) {

 	c := n.getController()

 	c.Lock()

+	defer c.Unlock()

 	sr, ok := c.svcRecords[n.ID()]

-	c.Unlock()

 	if !ok {

 		return nil, false

@@ -1621,7 +1631,6 @@ func (n *network) ResolveName(req string, ipType int) ([]net.IP, bool) {

 	req = strings.TrimSuffix(req, ".")

 	var ip []net.IP

-	n.Lock()

 	ip, ok = sr.svcMap[req]

 	if ipType == types.IPv6 {

@@ -1634,7 +1643,6 @@ func (n *network) ResolveName(req string, ipType int) ([]net.IP, bool) {

 		}

 		ip = sr.svcIPv6Map[req]

 	}

-	n.Unlock()

 	if ip != nil {

 		return ip, false

@@ -1643,13 +1651,28 @@ func (n *network) ResolveName(req string, ipType int) ([]net.IP, bool) {

 	return nil, ipv6Miss

 }

-func (n *network) ResolveIP(ip string) string {

-	var svc string

+func (n *network) HandleQueryResp(name string, ip net.IP) {

+	c := n.getController()

+	c.Lock()

+	defer c.Unlock()

+	sr, ok := c.svcRecords[n.ID()]

+	if !ok {

+		return

+	}

+

+	ipStr := netutils.ReverseIP(ip.String())

+

+	if ipInfo, ok := sr.ipMap[ipStr]; ok {

+		ipInfo.extResolver = true

+	}

+}

+

+func (n *network) ResolveIP(ip string) string {

 	c := n.getController()

 	c.Lock()

+	defer c.Unlock()

 	sr, ok := c.svcRecords[n.ID()]

-	c.Unlock()

 	if !ok {

 		return ""

@@ -1657,15 +1680,13 @@ func (n *network) ResolveIP(ip string) string {

 	nwName := n.Name()

-	n.Lock()

-	defer n.Unlock()

-	svc, ok = sr.ipMap[ip]

+	ipInfo, ok := sr.ipMap[ip]

-	if ok {

-		return svc + "." + nwName

+	if !ok || ipInfo.extResolver {

+		return ""

 	}

-	return svc

+	return ipInfo.name + "." + nwName

 }

 func (n *network) ResolveService(name string) ([]*net.SRV, []net.IP) {

@@ -1689,8 +1710,8 @@ func (n *network) ResolveService(name string) ([]*net.SRV, []net.IP) {

 	svcName := strings.Join(parts[2:], ".")

 	c.Lock()

+	defer c.Unlock()

 	sr, ok := c.svcRecords[n.ID()]

-	c.Unlock()

 	if !ok {

 		return nil, nil

@@ -54,6 +54,9 @@ type DNSBackend interface {

 	ExecFunc(f func()) error

 	//NdotsSet queries the backends ndots dns option settings

 	NdotsSet() bool

+	// HandleQueryResp passes the name & IP from a response to the backend. backend

+	// can use it to maintain any required state about the resolution

+	HandleQueryResp(name string, ip net.IP)

 }

 const (

@@ -462,9 +465,20 @@ func (r *resolver) ServeDNS(w dns.ResponseWriter, query *dns.Msg) {

 				logrus.Debugf("Read from DNS server failed, %s", err)

 				continue

 			}

-

 			r.forwardQueryEnd()

-

+			if resp != nil {

+				for _, rr := range resp.Answer {

+					h := rr.Header()

+					switch h.Rrtype {

+					case dns.TypeA:

+						ip := rr.(*dns.A).A

+						r.backend.HandleQueryResp(h.Name, ip)

+					case dns.TypeAAAA:

+						ip := rr.(*dns.AAAA).AAAA

+						r.backend.HandleQueryResp(h.Name, ip)

+					}

+				}

+			}

 			resp.Compress = true

 			break

 		}

@@ -411,6 +411,13 @@ func (sb *sandbox) updateGateway(ep *endpoint) error {

 	return nil

 }

+func (sb *sandbox) HandleQueryResp(name string, ip net.IP) {

+	for _, ep := range sb.getConnectedEndpoints() {

+		n := ep.getNetwork()

+		n.HandleQueryResp(name, ip)

+	}

+}

+

 func (sb *sandbox) ResolveIP(ip string) string {

 	var svc string

 	logrus.Debugf("IP To resolve %v", ip)