diff --git a/extras/outbounds/ob_direct.go b/extras/outbounds/ob_direct.go
index 60bce09..f7622b2 100644
--- a/extras/outbounds/ob_direct.go
+++ b/extras/outbounds/ob_direct.go
@@ -29,7 +29,6 @@ type directOutbound struct {
 	DeviceName string // For UDP binding
 }
 
-/*
 // NewDirectOutboundSimple creates a new directOutbound with the given mode,
 // without binding to a specific device. Works on all platforms.
 func NewDirectOutboundSimple(mode DirectOutboundMode) PluggableOutbound {
@@ -40,7 +39,6 @@ func NewDirectOutboundSimple(mode DirectOutboundMode) PluggableOutbound {
 		},
 	}
 }
-*/
 
 // resolve is our built-in DNS resolver for handling the case when
 // AddrEx.ResolveInfo is nil.
@@ -51,23 +49,14 @@ func (d *directOutbound) resolve(reqAddr *AddrEx) {
 		return
 	}
 	r := &ResolveInfo{}
-	for _, ip := range ips {
-		if r.IPv4 == nil && ip.To4() != nil {
-			r.IPv4 = ip
-		}
-		if r.IPv6 == nil && ip.To4() == nil {
-			// We must NOT use ip.To16() here because it will always
-			// return a 16-byte slice, even if the original IP is IPv4.
-			r.IPv6 = ip
-		}
-		if r.IPv4 != nil && r.IPv6 != nil {
-			break
-		}
+	r.IPv4, r.IPv6 = splitIPv4IPv6(ips)
+	if r.IPv4 == nil && r.IPv6 == nil {
+		r.Err = errors.New("no IPv4 or IPv6 address available")
 	}
 	reqAddr.ResolveInfo = r
 }
 
-func (d *directOutbound) DialTCP(reqAddr *AddrEx) (net.Conn, error) {
+func (d *directOutbound) TCP(reqAddr *AddrEx) (net.Conn, error) {
 	if reqAddr.ResolveInfo == nil {
 		// AddrEx.ResolveInfo is nil (no resolver in the pipeline),
 		// we need to resolve the address ourselves.
@@ -252,7 +241,7 @@ func (u *directOutboundUDPConn) Close() error {
 	return u.UDPConn.Close()
 }
 
-func (d *directOutbound) ListenUDP() (UDPConn, error) {
+func (d *directOutbound) UDP(reqAddr *AddrEx) (UDPConn, error) {
 	c, err := net.ListenUDP("udp", nil)
 	if err != nil {
 		return nil, err
diff --git a/extras/outbounds/utils.go b/extras/outbounds/utils.go
new file mode 100644
index 0000000..01a8b94
--- /dev/null
+++ b/extras/outbounds/utils.go
@@ -0,0 +1,24 @@
+package outbounds
+
+import "net"
+
+// splitIPv4IPv6 gets the first IPv4 and IPv6 address from a list of IP addresses.
+// Both of the return values can be nil when no IPv4 or IPv6 address is found.
+func splitIPv4IPv6(ips []net.IP) (ipv4, ipv6 net.IP) {
+	for _, ip := range ips {
+		if ip.To4() != nil {
+			if ipv4 == nil {
+				ipv4 = ip
+			}
+		} else {
+			if ipv6 == nil {
+				ipv6 = ip
+			}
+		}
+		if ipv4 != nil && ipv6 != nil {
+			// We have everything we need.
+			break
+		}
+	}
+	return
+}
diff --git a/extras/outbounds/utils_test.go b/extras/outbounds/utils_test.go
new file mode 100644
index 0000000..280a600
--- /dev/null
+++ b/extras/outbounds/utils_test.go
@@ -0,0 +1,84 @@
+package outbounds
+
+import (
+	"net"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSplitIPv4IPv6(t *testing.T) {
+	type args struct {
+		ips []net.IP
+	}
+	tests := []struct {
+		name     string
+		args     args
+		wantIpv4 net.IP
+		wantIpv6 net.IP
+	}{
+		{
+			name: "IPv4 only",
+			args: args{
+				ips: []net.IP{
+					net.ParseIP("4.5.6.7"),
+					net.ParseIP("9.9.9.9"),
+				},
+			},
+			wantIpv4: net.ParseIP("4.5.6.7"),
+			wantIpv6: nil,
+		},
+		{
+			name: "IPv6 only",
+			args: args{
+				ips: []net.IP{
+					net.ParseIP("2001:db8::68"),
+					net.ParseIP("2001:db8::69"),
+				},
+			},
+			wantIpv4: nil,
+			wantIpv6: net.ParseIP("2001:db8::68"),
+		},
+		{
+			name: "Both 1",
+			args: args{
+				ips: []net.IP{
+					net.ParseIP("2001:db8::68"),
+					net.ParseIP("2001:db8::69"),
+					net.ParseIP("4.5.6.7"),
+					net.ParseIP("9.9.9.9"),
+				},
+			},
+			wantIpv4: net.ParseIP("4.5.6.7"),
+			wantIpv6: net.ParseIP("2001:db8::68"),
+		},
+		{
+			name: "Both 2",
+			args: args{
+				ips: []net.IP{
+					net.ParseIP("2001:db8::69"),
+					net.ParseIP("9.9.9.9"),
+					net.ParseIP("2001:db8::68"),
+					net.ParseIP("4.5.6.7"),
+				},
+			},
+			wantIpv4: net.ParseIP("9.9.9.9"),
+			wantIpv6: net.ParseIP("2001:db8::69"),
+		},
+		{
+			name: "Empty",
+			args: args{
+				ips: []net.IP{},
+			},
+			wantIpv4: nil,
+			wantIpv6: nil,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotIpv4, gotIpv6 := splitIPv4IPv6(tt.args.ips)
+			assert.Equalf(t, tt.wantIpv4, gotIpv4, "splitIPv4IPv6(%v)", tt.args.ips)
+			assert.Equalf(t, tt.wantIpv6, gotIpv6, "splitIPv4IPv6(%v)", tt.args.ips)
+		})
+	}
+}