Added ip6tnlEncap to insert ip6tnl encap route

This commit added support to allow the operation of ip6tnl encapsulation.
It is equivalent to the iproute2 command, e.g., ip route add 192.168.99.0/24 encap ip6 dst 2001:db8:: dev ip6-tunnel
The limitation include that the options field defined in encap nl route attribute is not implenmented yet.
Testcase is included.

nl/ip6tnl_linux.go

@@ -0,0 +1,21 @@
+package nl
+
+// id's of route attribute from https://elixir.bootlin.com/linux/v5.17.3/source/include/uapi/linux/lwtunnel.h#L38
+// the value's size are specified in https://elixir.bootlin.com/linux/v5.17.3/source/net/ipv4/ip_tunnel_core.c#L928
+
+const (
+	LWTUNNEL_IP6_UNSPEC = iota
+	LWTUNNEL_IP6_ID
+	LWTUNNEL_IP6_DST
+	LWTUNNEL_IP6_SRC
+	LWTUNNEL_IP6_HOPLIMIT
+	LWTUNNEL_IP6_TC
+	LWTUNNEL_IP6_FLAGS
+	LWTUNNEL_IP6_PAD // not implemented
+	LWTUNNEL_IP6_OPTS // not implemented
+	__LWTUNNEL_IP6_MAX
+)
+
+
+
+

route_linux.go

@@ -590,6 +590,109 @@ func (e *BpfEncap) Equal(x Encap) bool {
 	return true
 }
 
+// IP6tnlEncap definition
+type IP6tnlEncap struct {
+
+	ID uint64
+	Dst net.IP
+	Src net.IP
+	Hoplimit uint8
+	TC uint8
+	Flags uint16
+
+}
+
+func (e *IP6tnlEncap) Type() int {
+	return nl.LWTUNNEL_ENCAP_IP6
+}
+
+func (e *IP6tnlEncap) Decode(buf []byte) error {
+	attrs, err := nl.ParseRouteAttr(buf)
+	if err != nil {
+		return err
+	}
+	for _, attr := range attrs {
+		switch attr.Attr.Type {
+		case nl.LWTUNNEL_IP6_ID:
+			e.ID = uint64(native.Uint64(attr.Value[0:4]))
+		case nl.LWTUNNEL_IP6_DST:
+			e.Dst = net.IP(attr.Value[:])
+		case nl.LWTUNNEL_IP6_SRC:
+			e.Src = net.IP(attr.Value[:])
+		case nl.LWTUNNEL_IP6_HOPLIMIT:
+			e.Hoplimit = attr.Value[0]
+		case nl.LWTUNNEL_IP6_TC:
+			e.TC = attr.Value[0]
+		case nl.LWTUNNEL_IP6_FLAGS:
+			e.Flags = uint16(native.Uint16(attr.Value[0:2]))
+		case nl.LWTUNNEL_IP6_PAD:
+			err = fmt.Errorf("decoding PAD in IP6tnlEncap is not supported",)
+		case nl.LWTUNNEL_IP6_OPTS:
+			err = fmt.Errorf("decoding OPTS in IP6tnlEncap is not supported")
+		}
+	}
+	return err
+}
+
+func (e *IP6tnlEncap) Encode() ([]byte, error) {
+
+	final := []byte{}
+
+	resID := make([]byte, 12)
+	native.PutUint16(resID, 12) //  2+2+8
+	native.PutUint16(resID[2:], nl.LWTUNNEL_IP6_ID)
+	native.PutUint64(resID[4:], 0)
+	final = append(final,resID...)
+
+	resDst := make([]byte, 4)
+	native.PutUint16(resDst, 20) //  2+2+16
+	native.PutUint16(resDst[2:], nl.LWTUNNEL_IP6_DST)
+	resDst = append(resDst, e.Dst...)
+	final = append(final,resDst...)
+
+	resSrc := make([]byte, 4)
+	native.PutUint16(resSrc, 20)
+	native.PutUint16(resSrc[2:], nl.LWTUNNEL_IP6_SRC)
+	resSrc = append(resSrc, e.Src...)
+	final = append(final,resSrc...)
+
+	resTc := make([]byte, 5)
+	native.PutUint16(resTc, 5)
+	native.PutUint16(resTc[2:], nl.LWTUNNEL_IP6_TC)
+	resTc[4] = e.TC
+	final = append(final,resTc...)
+
+	resHops := make([]byte, 5)
+	native.PutUint16(resHops, 5)
+	native.PutUint16(resHops[2:], nl.LWTUNNEL_IP6_HOPLIMIT)
+	resHops[4] = e.Hoplimit
+	final = append(final,resHops...)
+
+	resFlags := make([]byte, 6)
+	native.PutUint16(resFlags, 6)
+	native.PutUint16(resFlags[2:], nl.LWTUNNEL_IP6_FLAGS)
+	native.PutUint16(resFlags[4:], e.Flags)
+	final = append(final,resFlags...)
+
+	return final, nil
+}
+
+func (e *IP6tnlEncap) String() string {
+	return fmt.Sprintf("id %d src %s dst %s hoplimit %d tc %d flags 0x%.4x", e.ID, e.Src, e.Dst, e.Hoplimit, e.TC, e.Flags)
+}
+
+func (e *IP6tnlEncap) Equal(x Encap) bool {
+	o, ok := x.(*IP6tnlEncap)
+	if !ok {
+		return false
+	}
+
+	if e.ID != o.ID || e.Flags != o.Flags || e.Hoplimit != o.Hoplimit || e.Src.Equal(o.Src) || e.Dst.Equal(o.Dst) || e.TC != o.TC {
+		return false
+	}
+	return true
+}
+
 type Via struct {
 	AddrFamily int
 	Addr       net.IP

route_test.go

@@ -968,6 +968,66 @@ func TestMPLSRouteAddDel(t *testing.T) {
 
 }
 
+func TestIP6tnlRouteAddDel(t *testing.T) {
+	_, err := RouteList(nil, FAMILY_V4)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tearDown := setUpNetlinkTest(t)
+	defer tearDown()
+
+	// get loopback interface
+	link, err := LinkByName("lo")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// bring the interface up
+	if err := LinkSetUp(link); err != nil {
+		t.Fatal(err)
+	}
+
+	_, dst, err := net.ParseCIDR("192.168.99.0/24")
+	if err != nil {
+		t.Fatalf("cannot parse destination prefix: %v", err)
+	}
+
+	encap := IP6tnlEncap{
+		Dst: net.ParseIP("2001:db8::"),
+		Src: net.ParseIP("::"),
+	}
+
+	route := &Route{
+		LinkIndex: link.Attrs().Index,
+		Dst:       dst,
+		Encap:     &encap,
+	}
+
+	if err := RouteAdd(route); err != nil {
+		t.Fatalf("Cannot add route: %v", err)
+	}
+	routes, err := RouteList(link, FAMILY_V4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(routes) != 1 {
+		t.Fatal("Route not added properly")
+	}
+
+	if err := RouteDel(route); err != nil {
+		t.Fatal(err)
+	}
+	routes, err = RouteList(link, FAMILY_V4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(routes) != 0 {
+		t.Fatal("Route not removed properly")
+	}
+
+}
+
 func TestRouteEqual(t *testing.T) {
 	mplsDst := 100
 	seg6encap := &SEG6Encap{Mode: nl.SEG6_IPTUN_MODE_ENCAP}