diff --git a/dns/cache.go b/dns/cache.go
index 50b371a..03be604 100644
--- a/dns/cache.go
+++ b/dns/cache.go
@@ -42,20 +42,18 @@ func (c *Cache) Len() int {
 	return len(c.m)
 }
 
-// Put an item into cache, invalid after ttl seconds, never invalid if ttl=0
+// Put an item into cache, invalid after ttl seconds
 func (c *Cache) Put(k string, v []byte, ttl int) {
-	if len(v) == 0 {
-		return
+	if len(v) != 0 {
+		c.l.Lock()
+		it, ok := c.m[k]
+		if !ok {
+			it = &item{value: v}
+			c.m[k] = it
+		}
+		it.expire = time.Now().Add(time.Duration(ttl) * time.Second)
+		c.l.Unlock()
 	}
-
-	c.l.Lock()
-	it, ok := c.m[k]
-	if !ok {
-		it = &item{value: v}
-		c.m[k] = it
-	}
-	it.expire = time.Now().Add(time.Duration(ttl) * time.Second)
-	c.l.Unlock()
 }
 
 // Get an item from cache
diff --git a/dns/client.go b/dns/client.go
index f87da5a..6780549 100644
--- a/dns/client.go
+++ b/dns/client.go
@@ -41,7 +41,7 @@ func NewClient(dialer proxy.Dialer, upServers []string) (*Client, error) {
 
 // Exchange handles request msg and returns response msg
 // reqBytes = reqLen + reqMsg
-func (c *Client) Exchange(reqBytes []byte, clientAddr string) ([]byte, error) {
+func (c *Client) Exchange(reqBytes []byte, clientAddr string, preferTCP bool) ([]byte, error) {
 	req, err := UnmarshalMessage(reqBytes[2:])
 	if err != nil {
 		return nil, err
@@ -58,37 +58,14 @@ func (c *Client) Exchange(reqBytes []byte, clientAddr string) ([]byte, error) {
 		}
 	}
 
-	dnsServer := c.GetServer(req.Question.QNAME)
-	rc, err := c.dialer.NextDialer(req.Question.QNAME+":53").Dial("tcp", dnsServer)
+	dnsServer, network, respBytes, err := c.exchange(req.Question.QNAME, reqBytes, preferTCP)
 	if err != nil {
-		log.F("[dns] failed to connect to server %v: %v", dnsServer, err)
-		return nil, err
-	}
-	defer rc.Close()
-
-	if err = binary.Write(rc, binary.BigEndian, reqBytes); err != nil {
-		log.F("[dns] failed to write req message: %v", err)
-		return nil, err
-	}
-
-	var respLen uint16
-	if err = binary.Read(rc, binary.BigEndian, &respLen); err != nil {
-		log.F("[dns] failed to read response length: %v", err)
-		return nil, err
-	}
-
-	respBytes := make([]byte, respLen+2)
-	binary.BigEndian.PutUint16(respBytes[:2], respLen)
-
-	_, err = io.ReadFull(rc, respBytes[2:])
-	if err != nil {
-		log.F("[dns] error in read respMsg %s\n", err)
 		return nil, err
 	}
 
 	if req.Question.QTYPE != QTypeA && req.Question.QTYPE != QTypeAAAA {
-		log.F("[dns] %s <-> %s, type: %d, %s",
-			clientAddr, dnsServer, req.Question.QTYPE, req.Question.QNAME)
+		log.F("[dns] %s <-> %s(%s), type: %d, %s",
+			clientAddr, dnsServer, network, req.Question.QTYPE, req.Question.QNAME)
 		return respBytes, nil
 	}
 
@@ -104,28 +81,101 @@ func (c *Client) Exchange(reqBytes []byte, clientAddr string) ([]byte, error) {
 			for _, h := range c.handlers {
 				h(resp.Question.QNAME, answer.IP)
 			}
-
 			if answer.IP != "" {
 				ips = append(ips, answer.IP)
 			}
-
 			if answer.TTL != 0 {
 				ttl = int(answer.TTL)
 			}
-
 		}
-
 	}
 
 	// add to cache
-	c.cache.Put(getKey(resp.Question), respBytes, ttl)
+	if len(ips) != 0 {
+		c.cache.Put(getKey(resp.Question), respBytes, ttl)
+	}
 
-	log.F("[dns] %s <-> %s, type: %d, %s: %s",
-		clientAddr, dnsServer, resp.Question.QTYPE, resp.Question.QNAME, strings.Join(ips, ","))
+	log.F("[dns] %s <-> %s(%s), type: %d, %s: %s",
+		clientAddr, dnsServer, network, resp.Question.QTYPE, resp.Question.QNAME, strings.Join(ips, ","))
 
 	return respBytes, nil
 }
 
+// exchange choose a upstream dns server based on qname, communicate with it on the network
+func (c *Client) exchange(qname string, reqBytes []byte, preferTCP bool) (server, network string, respBytes []byte, err error) {
+	// use tcp to connect upstream server default
+	network = "tcp"
+
+	dialer := c.dialer.NextDialer(qname + ":53")
+
+	// If client uses udp and no forwarders specified, use udp
+	if !preferTCP && dialer.Addr() == "DIRECT" {
+		network = "udp"
+	}
+
+	server = c.GetServer(qname)
+	rc, err := dialer.Dial(network, server)
+	if err != nil {
+		log.F("[dns] failed to connect to server %v: %v", server, err)
+		return
+	}
+
+	switch network {
+	case "tcp":
+		respBytes, err = c.exchangeTCP(rc, reqBytes)
+	case "udp":
+		respBytes, err = c.exchangeUDP(rc, reqBytes)
+	}
+
+	return
+}
+
+// exchangeTCP exchange with server over tcp
+func (c *Client) exchangeTCP(rc net.Conn, reqBytes []byte) ([]byte, error) {
+	defer rc.Close()
+
+	if _, err := rc.Write(reqBytes); err != nil {
+		log.F("[dns] failed to write req message: %v", err)
+		return nil, err
+	}
+
+	var respLen uint16
+	if err := binary.Read(rc, binary.BigEndian, &respLen); err != nil {
+		log.F("[dns] failed to read response length: %v", err)
+		return nil, err
+	}
+
+	respBytes := make([]byte, respLen+2)
+	binary.BigEndian.PutUint16(respBytes[:2], respLen)
+
+	_, err := io.ReadFull(rc, respBytes[2:])
+	if err != nil {
+		log.F("[dns] error in read respMsg %s\n", err)
+		return nil, err
+	}
+
+	return respBytes, nil
+}
+
+// exchangeUDP exchange with server over udp
+func (c *Client) exchangeUDP(rc net.Conn, reqBytes []byte) ([]byte, error) {
+	defer rc.Close()
+
+	if _, err := rc.Write(reqBytes[2:]); err != nil {
+		log.F("[dns] failed to write req message: %v", err)
+		return nil, err
+	}
+
+	reqBytes = make([]byte, 2+UDPMaxLen)
+	n, err := rc.Read(reqBytes[2:])
+	if err != nil {
+		return nil, err
+	}
+	binary.BigEndian.PutUint16(reqBytes[:2], uint16(n))
+
+	return reqBytes[:2+n], nil
+}
+
 // SetServer .
 func (c *Client) SetServer(domain string, servers ...string) {
 	c.upServerMap[domain] = append(c.upServerMap[domain], servers...)
@@ -193,7 +243,7 @@ func (c *Client) GenResponse(domain string, ip string) (*Message, error) {
 
 	m := NewMessage(0, Response)
 	m.SetQuestion(NewQuestion(qtype, domain))
-	rr := &RR{NAME: domain, TYPE: qtype, CLASS: CLASSIN,
+	rr := &RR{NAME: domain, TYPE: qtype, CLASS: ClassINET,
 		RDLENGTH: rdlen, RDATA: rdata}
 	m.AddAnswer(rr)
 
diff --git a/dns/message.go b/dns/message.go
index 8730863..c583c2c 100644
--- a/dns/message.go
+++ b/dns/message.go
@@ -31,8 +31,8 @@ const (
 	QTypeAAAA uint16 = 28 ///ipv6
 )
 
-// CLASSIN .
-const CLASSIN uint16 = 1
+// ClassINET .
+const ClassINET uint16 = 1
 
 // Message format
 // https://tools.ietf.org/html/rfc1035#section-4.1
@@ -51,7 +51,7 @@ const CLASSIN uint16 = 1
 //     +---------------------+
 //     |      Additional     | RRs holding additional information
 type Message struct {
-	*Header
+	Header
 	// most dns implementation only support 1 question
 	Question   *Question
 	Answers    []*RR
@@ -68,10 +68,10 @@ func NewMessage(id uint16, msgType int) *Message {
 		id = uint16(rand.Uint32())
 	}
 
-	h := &Header{ID: id}
-	h.SetMsgType(msgType)
+	m := &Message{Header: Header{ID: id}}
+	m.SetMsgType(msgType)
 
-	return &Message{Header: h}
+	return m
 }
 
 // SetQuestion sets a question to dns message,
@@ -119,38 +119,35 @@ func (m *Message) Marshal() ([]byte, error) {
 
 // UnmarshalMessage unmarshals []bytes to Message
 func UnmarshalMessage(b []byte) (*Message, error) {
-	msg := &Message{Header: &Header{}}
-	msg.unMarshaled = b
-
-	err := UnmarshalHeader(b[:HeaderLen], msg.Header)
+	m := &Message{unMarshaled: b}
+	err := UnmarshalHeader(b[:HeaderLen], &m.Header)
 	if err != nil {
 		return nil, err
 	}
 
 	q := &Question{}
-	qLen, err := msg.UnmarshalQuestion(b[HeaderLen:], q)
+	qLen, err := m.UnmarshalQuestion(b[HeaderLen:], q)
 	if err != nil {
 		return nil, err
 	}
-
-	msg.SetQuestion(q)
+	m.SetQuestion(q)
 
 	// resp answers
-	rridx := HeaderLen + qLen
-	for i := 0; i < int(msg.Header.ANCOUNT); i++ {
+	rrIdx := HeaderLen + qLen
+	for i := 0; i < int(m.Header.ANCOUNT); i++ {
 		rr := &RR{}
-		rrLen, err := msg.UnmarshalRR(rridx, rr)
+		rrLen, err := m.UnmarshalRR(rrIdx, rr)
 		if err != nil {
 			return nil, err
 		}
-		msg.AddAnswer(rr)
+		m.AddAnswer(rr)
 
-		rridx += rrLen
+		rrIdx += rrLen
 	}
 
-	msg.Header.SetAncount(len(msg.Answers))
+	m.Header.SetAncount(len(m.Answers))
 
-	return msg, nil
+	return m, nil
 }
 
 // Header format
@@ -262,7 +259,7 @@ func NewQuestion(qtype uint16, domain string) *Question {
 	return &Question{
 		QNAME:  domain,
 		QTYPE:  qtype,
-		QCLASS: CLASSIN,
+		QCLASS: ClassINET,
 	}
 }
 
@@ -428,7 +425,9 @@ func (m *Message) UnmarshalDomain(b []byte) (string, int, error) {
 			if size == 0 {
 				idx++
 				break
-			} else if size > 63 {
+			}
+
+			if size > 63 {
 				return "", 0, errors.New("UnmarshalDomain: label size larger than 63")
 			}
 
diff --git a/dns/server.go b/dns/server.go
index 77717ed..1b6a998 100644
--- a/dns/server.go
+++ b/dns/server.go
@@ -61,11 +61,10 @@ func (s *Server) ListenAndServeUDP() {
 			log.F("[dns] not enough message data")
 			continue
 		}
-
 		binary.BigEndian.PutUint16(reqBytes[:2], reqLen)
 
 		go func() {
-			respBytes, err := s.Client.Exchange(reqBytes[:2+n], caddr.String())
+			respBytes, err := s.Client.Exchange(reqBytes[:2+n], caddr.String(), false)
 			if err != nil {
 				log.F("[dns] error in exchange: %s", err)
 				return
@@ -123,7 +122,7 @@ func (s *Server) ServeTCP(c net.Conn) {
 
 	binary.BigEndian.PutUint16(reqBytes[:2], reqLen)
 
-	respBytes, err := s.Exchange(reqBytes, c.RemoteAddr().String())
+	respBytes, err := s.Exchange(reqBytes, c.RemoteAddr().String(), true)
 	if err != nil {
 		log.F("[dns]-tcp error in exchange: %s", err)
 		return