diff --git a/clientconn.go b/clientconn.go
index 00a3b8d8..b2ff4292 100644
--- a/clientconn.go
+++ b/clientconn.go
@@ -37,6 +37,7 @@ import (
 	"errors"
 	"log"
 	"net"
+	"strings"
 	"sync"
 	"time"
 
@@ -96,11 +97,11 @@ func WithTimeout(d time.Duration) DialOption {
 	}
 }
 
-// WithNetwork returns a DialOption that specifies the network on which
-// the connection will be established.
-func WithNetwork(network string) DialOption {
+// WithDialer returns a DialOption that defines a function which takes an
+// address and turns it into a net.Conn.
+func WithDialer(f func(addr string, timeout time.Duration) (net.Conn, error)) DialOption {
 	return func(o *dialOptions) {
-		o.copts.Network = network
+		o.copts.Dialer = f
 	}
 }
 
@@ -117,24 +118,11 @@ func Dial(target string, opts ...DialOption) (*ClientConn, error) {
 	for _, opt := range opts {
 		opt(&cc.dopts)
 	}
-	// Validate the network type
-	switch cc.dopts.copts.Network {
-	case "":
-		cc.dopts.copts.Network = "tcp"  // Set the default
-	case "tcp", "tcp4", "tcp6", "unix":
-	default:
-		return nil, net.UnknownNetworkError(cc.dopts.copts.Network)
-	}
-	cc.authority = target
-	// Format target for tcp.
-	if cc.dopts.copts.Network != "unix" {
-		// format target for tcp.
-		var err error
-		cc.authority, _, err = net.SplitHostPort(target)
-		if err != nil {
-			return nil, err
-		}
+	colonPos := strings.LastIndex(target, ":")
+	if colonPos == -1 {
+		colonPos = len(target)
 	}
+	cc.authority = target[:colonPos]
 	if cc.dopts.codec == nil {
 		// Set the default codec.
 		cc.dopts.codec = protoCodec{}
diff --git a/credentials/credentials.go b/credentials/credentials.go
index fae0a302..aeab6737 100644
--- a/credentials/credentials.go
+++ b/credentials/credentials.go
@@ -43,6 +43,8 @@ import (
 	"fmt"
 	"io/ioutil"
 	"net"
+	"strings"
+	"time"
 
 	"golang.org/x/net/context"
 	"golang.org/x/oauth2"
@@ -71,15 +73,10 @@ type Credentials interface {
 // TransportAuthenticator defines the common interface all supported transport
 // authentication protocols (e.g., TLS, SSL) must implement.
 type TransportAuthenticator interface {
-	// Dial connects to the given network address using net.Dial and then
+	// Dial connects to the given network address using dialer and then
 	// does the authentication handshake specified by the corresponding
 	// authentication protocol.
-	Dial(network, addr string) (net.Conn, error)
-	// DialWithDialer connects to the given network address using
-	// dialer.Dial does the authentication handshake specified by the
-	// corresponding authentication protocol. Any timeout or deadline
-	// given in the dialer apply to connection and handshake as a whole.
-	DialWithDialer(dialer *net.Dialer, network, addr string) (net.Conn, error)
+	Dial(dialer func(string, time.Duration) (net.Conn, error), addr string, timeout time.Duration) (net.Conn, error)
 	// NewListener creates a listener which accepts connections with requested
 	// authentication handshake.
 	NewListener(lis net.Listener) net.Listener
@@ -98,19 +95,46 @@ func (c *tlsCreds) GetRequestMetadata(ctx context.Context) (map[string]string, e
 	return nil, nil
 }
 
-func (c *tlsCreds) DialWithDialer(dialer *net.Dialer, network, addr string) (_ net.Conn, err error) {
-	if c.config.ServerName == "" {
-		c.config.ServerName, _, err = net.SplitHostPort(addr)
-		if err != nil {
-			return nil, fmt.Errorf("credentials: failed to parse server address %v", err)
-		}
-	}
-	return tls.DialWithDialer(dialer, network, addr, &c.config)
-}
+type timeoutError struct{}
 
-// Dial connects to addr and performs TLS handshake.
-func (c *tlsCreds) Dial(network, addr string) (_ net.Conn, err error) {
-	return c.DialWithDialer(new(net.Dialer), network, addr)
+func (timeoutError) Error() string   { return "credentials: Dial timed out" }
+func (timeoutError) Timeout() bool   { return true }
+func (timeoutError) Temporary() bool { return true }
+
+func (c *tlsCreds) Dial(dialer func(addr string, timeout time.Duration) (net.Conn, error), addr string, timeout time.Duration) (net.Conn, error) {
+	// borrow some code from tls.DialWithDialer
+	var errChannel chan error
+	if timeout != 0 {
+		errChannel = make(chan error, 2)
+		time.AfterFunc(timeout, func() {
+			errChannel <- timeoutError{}
+		})
+	}
+	rawConn, err := dialer(addr, timeout)
+	if err != nil {
+		return nil, err
+	}
+	if c.config.ServerName == "" {
+		colonPos := strings.LastIndex(addr, ":")
+		if colonPos == -1 {
+			colonPos = len(addr)
+		}
+		c.config.ServerName = addr[:colonPos]
+	}
+	conn := tls.Client(rawConn, &c.config)
+	if timeout == 0 {
+		err = conn.Handshake()
+	} else {
+		go func() {
+			errChannel <- conn.Handshake()
+		}()
+		err = <-errChannel
+	}
+	if err != nil {
+		rawConn.Close()
+		return nil, err
+	}
+	return conn, nil
 }
 
 // NewListener creates a net.Listener using the information in tlsCreds.
diff --git a/test/end2end_test.go b/test/end2end_test.go
index 9e8abf5b..3d41c610 100644
--- a/test/end2end_test.go
+++ b/test/end2end_test.go
@@ -266,16 +266,21 @@ func TestReconnectTimeout(t *testing.T) {
 	}
 }
 
+func unixDialer(addr string, timeout time.Duration) (net.Conn, error) {
+	return net.DialTimeout("unix", addr, timeout)
+}
+
 type env struct {
 	network  string // The type of network such as tcp, unix, etc.
+	dialer   func(addr string, timeout time.Duration) (net.Conn, error)
 	security string // The security protocol such as TLS, SSH, etc.
 }
 
 func listTestEnv() []env {
 	if runtime.GOOS == "windows" {
-		return []env{env{"tcp", ""}, env{"tcp", "tls"}}
+		return []env{env{"tcp", nil, ""}, env{"tcp", nil, "tls"}}
 	}
-	return []env{env{"tcp", ""}, env{"tcp", "tls"}, env{"unix", ""}, env{"unix", "tls"}}
+	return []env{env{"tcp", nil, ""}, env{"tcp", nil, "tls"}, env{"unix", unixDialer, ""}, env{"unix", unixDialer, "tls"}}
 }
 
 func setUp(maxStream uint32, e env) (s *grpc.Server, cc *grpc.ClientConn) {
@@ -315,9 +320,9 @@ func setUp(maxStream uint32, e env) (s *grpc.Server, cc *grpc.ClientConn) {
 		if err != nil {
 			log.Fatalf("Failed to create credentials %v", err)
 		}
-		cc, err = grpc.Dial(addr, grpc.WithTransportCredentials(creds), grpc.WithNetwork(e.network))
+		cc, err = grpc.Dial(addr, grpc.WithTransportCredentials(creds), grpc.WithDialer(e.dialer))
 	} else {
-		cc, err = grpc.Dial(addr, grpc.WithNetwork(e.network))
+		cc, err = grpc.Dial(addr, grpc.WithDialer(e.dialer))
 	}
 	if err != nil {
 		log.Fatalf("Dial(%q) = %v", addr, err)
diff --git a/transport/http2_client.go b/transport/http2_client.go
index 136debfb..710908dd 100644
--- a/transport/http2_client.go
+++ b/transport/http2_client.go
@@ -98,6 +98,12 @@ type http2Client struct {
 // and starts to receive messages on it. Non-nil error returns if construction
 // fails.
 func newHTTP2Client(addr string, opts *ConnectOptions) (_ ClientTransport, err error) {
+	if opts.Dialer == nil {
+		// Set the default Dialer.
+		opts.Dialer = func(addr string, timeout time.Duration) (net.Conn, error) {
+			return net.DialTimeout("tcp", addr, timeout)
+		}
+	}
 	var (
 		connErr error
 		conn    net.Conn
@@ -110,12 +116,12 @@ func newHTTP2Client(addr string, opts *ConnectOptions) (_ ClientTransport, err e
 			// multiple ones provided. Revisit this if it is not appropriate. Probably
 			// place the ClientTransport construction into a separate function to make
 			// things clear.
-			conn, connErr = ccreds.DialWithDialer(&net.Dialer{Timeout: opts.Timeout}, opts.Network, addr)
+			conn, connErr = ccreds.Dial(opts.Dialer, addr, opts.Timeout)
 			break
 		}
 	}
 	if scheme == "http" {
-		conn, connErr = net.DialTimeout(opts.Network, addr, opts.Timeout)
+		conn, connErr = opts.Dialer(addr, opts.Timeout)
 	}
 	if connErr != nil {
 		return nil, ConnectionErrorf("transport: %v", connErr)
diff --git a/transport/transport.go b/transport/transport.go
index ebd36291..5dfd89f0 100644
--- a/transport/transport.go
+++ b/transport/transport.go
@@ -315,9 +315,7 @@ func NewServerTransport(protocol string, conn net.Conn, maxStreams uint32) (Serv
 
 // ConnectOptions covers all relevant options for dialing a server.
 type ConnectOptions struct {
-	// Network indicates the type of network where the connection is established.
-	// Known networks are "tcp", "tcp4", "tcp6", "unix"
-	Network     string
+	Dialer      func(string, time.Duration) (net.Conn, error)
 	AuthOptions []credentials.Credentials
 	Timeout     time.Duration
 }