Add multicast support

PiperOrigin-RevId: 212750821
Change-Id: I822fd63e48c684b45fd91f9ce057867b7eceb792

5 files changed, 315 insertions, 108 deletions

diff --git a/pkg/tcpip/transport/ping/endpoint.go b/pkg/tcpip/transport/ping/endpoint.go
index fc98c41eb..7aaf2d9c6 100644
--- a/pkg/tcpip/transport/ping/endpoint.go
+++ b/pkg/tcpip/transport/ping/endpoint.go
@@ -385,7 +385,7 @@ func sendPing4(r *stack.Route, ident uint16, data buffer.View) *tcpip.Error {
 	icmpv4.SetChecksum(^header.Checksum(icmpv4, header.Checksum(data, 0)))
 
 	vv := buffer.NewVectorisedView(len(data), []buffer.View{data})
-	return r.WritePacket(&hdr, vv, header.ICMPv4ProtocolNumber)
+	return r.WritePacket(&hdr, vv, header.ICMPv4ProtocolNumber, r.DefaultTTL())
 }
 
 func sendPing6(r *stack.Route, ident uint16, data buffer.View) *tcpip.Error {
@@ -408,8 +408,9 @@ func sendPing6(r *stack.Route, ident uint16, data buffer.View) *tcpip.Error {
 
 	icmpv6.SetChecksum(0)
 	icmpv6.SetChecksum(^header.Checksum(icmpv6, header.Checksum(data, 0)))
+
 	vv := buffer.NewVectorisedView(len(data), []buffer.View{data})
-	return r.WritePacket(&hdr, vv, header.ICMPv6ProtocolNumber)
+	return r.WritePacket(&hdr, vv, header.ICMPv6ProtocolNumber, r.DefaultTTL())
 }
 
 func (e *endpoint) checkV4Mapped(addr *tcpip.FullAddress, allowMismatch bool) (tcpip.NetworkProtocolNumber, *tcpip.Error) {
diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go
index de5f963cf..ce87d5818 100644
--- a/pkg/tcpip/transport/tcp/connect.go
+++ b/pkg/tcpip/transport/tcp/connect.go
@@ -563,14 +563,14 @@ func sendSynTCP(r *stack.Route, id stack.TransportEndpointID, flags byte, seq, a
 	}
 
 	options := makeSynOptions(opts)
-	err := sendTCPWithOptions(r, id, buffer.VectorisedView{}, flags, seq, ack, rcvWnd, options)
+	err := sendTCP(r, id, buffer.VectorisedView{}, r.DefaultTTL(), flags, seq, ack, rcvWnd, options)
 	putOptions(options)
 	return err
 }
 
-// sendTCPWithOptions sends a TCP segment with the provided options via the
-// provided network endpoint and under the provided identity.
-func sendTCPWithOptions(r *stack.Route, id stack.TransportEndpointID, data buffer.VectorisedView, flags byte, seq, ack seqnum.Value, rcvWnd seqnum.Size, opts []byte) *tcpip.Error {
+// sendTCP sends a TCP segment with the provided options via the provided
+// network endpoint and under the provided identity.
+func sendTCP(r *stack.Route, id stack.TransportEndpointID, data buffer.VectorisedView, ttl uint8, flags byte, seq, ack seqnum.Value, rcvWnd seqnum.Size, opts []byte) *tcpip.Error {
 	optLen := len(opts)
 	// Allocate a buffer for the TCP header.
 	hdr := buffer.NewPrependable(header.TCPMinimumSize + int(r.MaxHeaderLength()) + optLen)
@@ -608,48 +608,7 @@ func sendTCPWithOptions(r *stack.Route, id stack.TransportEndpointID, data buffe
 		r.Stats().TCP.ResetsSent.Increment()
 	}
 
-	return r.WritePacket(&hdr, data, ProtocolNumber)
-}
-
-// sendTCP sends a TCP segment via the provided network endpoint and under the
-// provided identity.
-func sendTCP(r *stack.Route, id stack.TransportEndpointID, payload buffer.VectorisedView, flags byte, seq, ack seqnum.Value, rcvWnd seqnum.Size) *tcpip.Error {
-	// Allocate a buffer for the TCP header.
-	hdr := buffer.NewPrependable(header.TCPMinimumSize + int(r.MaxHeaderLength()))
-
-	if rcvWnd > 0xffff {
-		rcvWnd = 0xffff
-	}
-
-	// Initialize the header.
-	tcp := header.TCP(hdr.Prepend(header.TCPMinimumSize))
-	tcp.Encode(&header.TCPFields{
-		SrcPort:    id.LocalPort,
-		DstPort:    id.RemotePort,
-		SeqNum:     uint32(seq),
-		AckNum:     uint32(ack),
-		DataOffset: header.TCPMinimumSize,
-		Flags:      flags,
-		WindowSize: uint16(rcvWnd),
-	})
-
-	// Only calculate the checksum if offloading isn't supported.
-	if r.Capabilities()&stack.CapabilityChecksumOffload == 0 {
-		length := uint16(hdr.UsedLength() + payload.Size())
-		xsum := r.PseudoHeaderChecksum(ProtocolNumber)
-		for _, v := range payload.Views() {
-			xsum = header.Checksum(v, xsum)
-		}
-
-		tcp.SetChecksum(^tcp.CalculateChecksum(xsum, length))
-	}
-
-	r.Stats().TCP.SegmentsSent.Increment()
-	if (flags & flagRst) != 0 {
-		r.Stats().TCP.ResetsSent.Increment()
-	}
-
-	return r.WritePacket(&hdr, payload, ProtocolNumber)
+	return r.WritePacket(&hdr, data, ProtocolNumber, ttl)
 }
 
 // makeOptions makes an options slice.
@@ -698,12 +657,7 @@ func (e *endpoint) sendRaw(data buffer.VectorisedView, flags byte, seq, ack seqn
 		sackBlocks = e.sack.Blocks[:e.sack.NumBlocks]
 	}
 	options := e.makeOptions(sackBlocks)
-	if len(options) > 0 {
-		err := sendTCPWithOptions(&e.route, e.id, data, flags, seq, ack, rcvWnd, options)
-		putOptions(options)
-		return err
-	}
-	err := sendTCP(&e.route, e.id, data, flags, seq, ack, rcvWnd)
+	err := sendTCP(&e.route, e.id, data, e.route.DefaultTTL(), flags, seq, ack, rcvWnd, options)
 	putOptions(options)
 	return err
 }
diff --git a/pkg/tcpip/transport/tcp/protocol.go b/pkg/tcpip/transport/tcp/protocol.go
index 006b2f074..fe21f2c78 100644
--- a/pkg/tcpip/transport/tcp/protocol.go
+++ b/pkg/tcpip/transport/tcp/protocol.go
@@ -147,7 +147,7 @@ func replyWithReset(s *segment) {
 
 	ack := s.sequenceNumber.Add(s.logicalLen())
 
-	sendTCP(&s.route, s.id, buffer.VectorisedView{}, flagRst|flagAck, seq, ack, 0)
+	sendTCP(&s.route, s.id, buffer.VectorisedView{}, s.route.DefaultTTL(), flagRst|flagAck, seq, ack, 0, nil)
 }
 
 // SetOption implements TransportProtocol.SetOption.
diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index d091a6196..5de518a55 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -70,19 +70,24 @@ type endpoint struct {
 	rcvTimestamp  bool
 
 	// The following fields are protected by the mu mutex.
-	mu         sync.RWMutex `state:"nosave"`
-	sndBufSize int
-	id         stack.TransportEndpointID
-	state      endpointState
-	bindNICID  tcpip.NICID
-	regNICID   tcpip.NICID
-	route      stack.Route `state:"manual"`
-	dstPort    uint16
-	v6only     bool
+	mu           sync.RWMutex `state:"nosave"`
+	sndBufSize   int
+	id           stack.TransportEndpointID
+	state        endpointState
+	bindNICID    tcpip.NICID
+	regNICID     tcpip.NICID
+	route        stack.Route `state:"manual"`
+	dstPort      uint16
+	v6only       bool
+	multicastTTL uint8
 
 	// shutdownFlags represent the current shutdown state of the endpoint.
 	shutdownFlags tcpip.ShutdownFlags
 
+	// multicastMemberships that need to be remvoed when the endpoint is
+	// closed. Protected by the mu mutex.
+	multicastMemberships []multicastMembership
+
 	// effectiveNetProtos contains the network protocols actually in use. In
 	// most cases it will only contain "netProto", but in cases like IPv6
 	// endpoints with v6only set to false, this could include multiple
@@ -92,11 +97,29 @@ type endpoint struct {
 	effectiveNetProtos []tcpip.NetworkProtocolNumber
 }
 
+type multicastMembership struct {
+	nicID         tcpip.NICID
+	multicastAddr tcpip.Address
+}
+
 func newEndpoint(stack *stack.Stack, netProto tcpip.NetworkProtocolNumber, waiterQueue *waiter.Queue) *endpoint {
 	return &endpoint{
-		stack:         stack,
-		netProto:      netProto,
-		waiterQueue:   waiterQueue,
+		stack:       stack,
+		netProto:    netProto,
+		waiterQueue: waiterQueue,
+		// RFC 1075 section 5.4 recommends a TTL of 1 for membership
+		// requests.
+		//
+		// RFC 5135 4.2.1 appears to assume that IGMP messages have a
+		// TTL of 1.
+		//
+		// RFC 5135 Appendix A defines TTL=1: A multicast source that
+		// wants its traffic to not traverse a router (e.g., leave a
+		// home network) may find it useful to send traffic with IP
+		// TTL=1.
+		//
+		// Linux defaults to TTL=1.
+		multicastTTL:  1,
 		rcvBufSizeMax: 32 * 1024,
 		sndBufSize:    32 * 1024,
 	}
@@ -135,6 +158,11 @@ func (e *endpoint) Close() {
 		e.stack.ReleasePort(e.effectiveNetProtos, ProtocolNumber, e.id.LocalAddress, e.id.LocalPort)
 	}
 
+	for _, mem := range e.multicastMemberships {
+		e.stack.LeaveGroup(e.netProto, mem.nicID, mem.multicastAddr)
+	}
+	e.multicastMemberships = nil
+
 	// Close the receive list and drain it.
 	e.rcvMu.Lock()
 	e.rcvClosed = true
@@ -329,8 +357,13 @@ func (e *endpoint) Write(p tcpip.Payload, opts tcpip.WriteOptions) (uintptr, *tc
 		return 0, err
 	}
 
+	ttl := route.DefaultTTL()
+	if header.IsV4MulticastAddress(route.RemoteAddress) || header.IsV6MulticastAddress(route.RemoteAddress) {
+		ttl = e.multicastTTL
+	}
+
 	vv := buffer.NewVectorisedView(len(v), []buffer.View{v})
-	if err := sendUDP(route, vv, e.id.LocalPort, dstPort); err != nil {
+	if err := sendUDP(route, vv, e.id.LocalPort, dstPort, ttl); err != nil {
 		return 0, err
 	}
 	return uintptr(len(v)), nil
@@ -365,6 +398,56 @@ func (e *endpoint) SetSockOpt(opt interface{}) *tcpip.Error {
 		e.rcvMu.Lock()
 		e.rcvTimestamp = v != 0
 		e.rcvMu.Unlock()
+
+	case tcpip.MulticastTTLOption:
+		e.mu.Lock()
+		defer e.mu.Unlock()
+		e.multicastTTL = uint8(v)
+
+	case tcpip.AddMembershipOption:
+		nicID := v.NIC
+		if v.InterfaceAddr != header.IPv4Any {
+			nicID = e.stack.CheckLocalAddress(nicID, e.netProto, v.InterfaceAddr)
+		}
+		if nicID == 0 {
+			return tcpip.ErrNoRoute
+		}
+
+		// TODO: check that v.MulticastAddr is a multicast address.
+		if err := e.stack.JoinGroup(e.netProto, nicID, v.MulticastAddr); err != nil {
+			return err
+		}
+
+		e.mu.Lock()
+		defer e.mu.Unlock()
+
+		e.multicastMemberships = append(e.multicastMemberships, multicastMembership{nicID, v.MulticastAddr})
+
+	case tcpip.RemoveMembershipOption:
+		nicID := v.NIC
+		if v.InterfaceAddr != header.IPv4Any {
+			nicID = e.stack.CheckLocalAddress(nicID, e.netProto, v.InterfaceAddr)
+		}
+		if nicID == 0 {
+			return tcpip.ErrNoRoute
+		}
+
+		// TODO: check that v.MulticastAddr is a multicast address.
+		if err := e.stack.LeaveGroup(e.netProto, nicID, v.MulticastAddr); err != nil {
+			return err
+		}
+
+		e.mu.Lock()
+		defer e.mu.Unlock()
+		for i, mem := range e.multicastMemberships {
+			if mem.nicID == nicID && mem.multicastAddr == v.MulticastAddr {
+				// Only remove the first match, so that each added membership above is
+				// paired with exactly 1 removal.
+				e.multicastMemberships[i] = e.multicastMemberships[len(e.multicastMemberships)-1]
+				e.multicastMemberships = e.multicastMemberships[:len(e.multicastMemberships)-1]
+				break
+			}
+		}
 	}
 	return nil
 }
@@ -421,6 +504,12 @@ func (e *endpoint) GetSockOpt(opt interface{}) *tcpip.Error {
 			*o = 1
 		}
 		e.rcvMu.Unlock()
+
+	case *tcpip.MulticastTTLOption:
+		e.mu.Lock()
+		*o = tcpip.MulticastTTLOption(e.multicastTTL)
+		e.mu.Unlock()
+		return nil
 	}
 
 	return tcpip.ErrUnknownProtocolOption
@@ -428,7 +517,7 @@ func (e *endpoint) GetSockOpt(opt interface{}) *tcpip.Error {
 
 // sendUDP sends a UDP segment via the provided network endpoint and under the
 // provided identity.
-func sendUDP(r *stack.Route, data buffer.VectorisedView, localPort, remotePort uint16) *tcpip.Error {
+func sendUDP(r *stack.Route, data buffer.VectorisedView, localPort, remotePort uint16, ttl uint8) *tcpip.Error {
 	// Allocate a buffer for the UDP header.
 	hdr := buffer.NewPrependable(header.UDPMinimumSize + int(r.MaxHeaderLength()))
 
@@ -454,7 +543,7 @@ func sendUDP(r *stack.Route, data buffer.VectorisedView, localPort, remotePort u
 	// Track count of packets sent.
 	r.Stats().UDP.PacketsSent.Increment()
 
-	return r.WritePacket(&hdr, data, ProtocolNumber)
+	return r.WritePacket(&hdr, data, ProtocolNumber, ttl)
 }
 
 func (e *endpoint) checkV4Mapped(addr *tcpip.FullAddress, allowMismatch bool) (tcpip.NetworkProtocolNumber, *tcpip.Error) {
@@ -581,7 +670,9 @@ func (e *endpoint) Shutdown(flags tcpip.ShutdownFlags) *tcpip.Error {
 	e.mu.Lock()
 	defer e.mu.Unlock()
 
-	if e.state != stateConnected {
+	// A socket in the bound state can still receive multicast messages,
+	// so we need to notify waiters on shutdown.
+	if e.state != stateBound && e.state != stateConnected {
 		return tcpip.ErrNotConnected
 	}
 
diff --git a/pkg/tcpip/transport/udp/udp_test.go b/pkg/tcpip/transport/udp/udp_test.go
index 4700193c2..6d7a737bd 100644
--- a/pkg/tcpip/transport/udp/udp_test.go
+++ b/pkg/tcpip/transport/udp/udp_test.go
@@ -34,16 +34,20 @@ import (
 )
 
 const (
-	stackV6Addr          = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01"
-	testV6Addr           = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02"
-	stackV4MappedAddr    = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff" + stackAddr
-	testV4MappedAddr     = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff" + testAddr
-	V4MappedWildcardAddr = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff\x00\x00\x00\x00"
-
-	stackAddr = "\x0a\x00\x00\x01"
-	stackPort = 1234
-	testAddr  = "\x0a\x00\x00\x02"
-	testPort  = 4096
+	stackV6Addr           = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01"
+	testV6Addr            = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02"
+	stackV4MappedAddr     = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff" + stackAddr
+	testV4MappedAddr      = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff" + testAddr
+	multicastV4MappedAddr = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff" + multicastAddr
+	V4MappedWildcardAddr  = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff\x00\x00\x00\x00"
+
+	stackAddr       = "\x0a\x00\x00\x01"
+	stackPort       = 1234
+	testAddr        = "\x0a\x00\x00\x02"
+	testPort        = 4096
+	multicastAddr   = "\xe8\x2b\xd3\xea"
+	multicastV6Addr = "\xff\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
+	multicastPort   = 1234
 
 	// defaultMTU is the MTU, in bytes, used throughout the tests, except
 	// where another value is explicitly used. It is chosen to match the MTU
@@ -128,37 +132,35 @@ func (c *testContext) createV6Endpoint(v6only bool) {
 	}
 }
 
-func (c *testContext) getV6Packet() []byte {
+func (c *testContext) getPacket(protocolNumber tcpip.NetworkProtocolNumber, multicast bool) []byte {
 	select {
 	case p := <-c.linkEP.C:
-		if p.Proto != ipv6.ProtocolNumber {
-			c.t.Fatalf("Bad network protocol: got %v, wanted %v", p.Proto, ipv6.ProtocolNumber)
+		if p.Proto != protocolNumber {
+			c.t.Fatalf("Bad network protocol: got %v, wanted %v", p.Proto, protocolNumber)
 		}
 		b := make([]byte, len(p.Header)+len(p.Payload))
 		copy(b, p.Header)
 		copy(b[len(p.Header):], p.Payload)
 
-		checker.IPv6(c.t, b, checker.SrcAddr(stackV6Addr), checker.DstAddr(testV6Addr))
-		return b
-
-	case <-time.After(2 * time.Second):
-		c.t.Fatalf("Packet wasn't written out")
-	}
-
-	return nil
-}
-
-func (c *testContext) getPacket() []byte {
-	select {
-	case p := <-c.linkEP.C:
-		if p.Proto != ipv4.ProtocolNumber {
-			c.t.Fatalf("Bad network protocol: got %v, wanted %v", p.Proto, ipv4.ProtocolNumber)
+		var checkerFn func(*testing.T, []byte, ...checker.NetworkChecker)
+		var srcAddr, dstAddr tcpip.Address
+		switch protocolNumber {
+		case ipv4.ProtocolNumber:
+			checkerFn = checker.IPv4
+			srcAddr, dstAddr = stackAddr, testAddr
+			if multicast {
+				dstAddr = multicastAddr
+			}
+		case ipv6.ProtocolNumber:
+			checkerFn = checker.IPv6
+			srcAddr, dstAddr = stackV6Addr, testV6Addr
+			if multicast {
+				dstAddr = multicastV6Addr
+			}
+		default:
+			c.t.Fatalf("unknown protocol %d", protocolNumber)
 		}
-		b := make([]byte, len(p.Header)+len(p.Payload))
-		copy(b, p.Header)
-		copy(b[len(p.Header):], p.Payload)
-
-		checker.IPv4(c.t, b, checker.SrcAddr(stackAddr), checker.DstAddr(testAddr))
+		checkerFn(c.t, b, checker.SrcAddr(srcAddr), checker.DstAddr(dstAddr))
 		return b
 
 	case <-time.After(2 * time.Second):
@@ -495,7 +497,7 @@ func testV4Write(c *testContext) uint16 {
 	}
 
 	// Check that we received the packet.
-	b := c.getPacket()
+	b := c.getPacket(ipv4.ProtocolNumber, false)
 	udp := header.UDP(header.IPv4(b).Payload())
 	checker.IPv4(c.t, b,
 		checker.UDP(
@@ -525,7 +527,7 @@ func testV6Write(c *testContext) uint16 {
 	}
 
 	// Check that we received the packet.
-	b := c.getV6Packet()
+	b := c.getPacket(ipv6.ProtocolNumber, false)
 	udp := header.UDP(header.IPv6(b).Payload())
 	checker.IPv6(c.t, b,
 		checker.UDP(
@@ -682,7 +684,7 @@ func TestV6WriteOnConnected(t *testing.T) {
 	}
 
 	// Check that we received the packet.
-	b := c.getV6Packet()
+	b := c.getPacket(ipv6.ProtocolNumber, false)
 	udp := header.UDP(header.IPv6(b).Payload())
 	checker.IPv6(c.t, b,
 		checker.UDP(
@@ -718,7 +720,7 @@ func TestV4WriteOnConnected(t *testing.T) {
 	}
 
 	// Check that we received the packet.
-	b := c.getPacket()
+	b := c.getPacket(ipv4.ProtocolNumber, false)
 	udp := header.UDP(header.IPv4(b).Payload())
 	checker.IPv4(c.t, b,
 		checker.UDP(
@@ -769,3 +771,162 @@ func TestWriteIncrementsPacketsSent(t *testing.T) {
 		c.t.Fatalf("Write did not increment PacketsSent: got %v, want %v", got, want)
 	}
 }
+
+func TestTTL(t *testing.T) {
+	payload := tcpip.SlicePayload(buffer.View(newPayload()))
+
+	for _, name := range []string{"v4", "v6", "dual"} {
+		t.Run(name, func(t *testing.T) {
+			var networkProtocolNumber tcpip.NetworkProtocolNumber
+			switch name {
+			case "v4":
+				networkProtocolNumber = ipv4.ProtocolNumber
+			case "v6", "dual":
+				networkProtocolNumber = ipv6.ProtocolNumber
+			default:
+				t.Fatal("unknown test variant")
+			}
+
+			var variants []string
+			switch name {
+			case "v4":
+				variants = []string{"v4"}
+			case "v6":
+				variants = []string{"v6"}
+			case "dual":
+				variants = []string{"v6", "mapped"}
+			}
+
+			for _, variant := range variants {
+				t.Run(variant, func(t *testing.T) {
+					for _, typ := range []string{"unicast", "multicast"} {
+						t.Run(typ, func(t *testing.T) {
+							var addr tcpip.Address
+							var port uint16
+							switch typ {
+							case "unicast":
+								port = testPort
+								switch variant {
+								case "v4":
+									addr = testAddr
+								case "mapped":
+									addr = testV4MappedAddr
+								case "v6":
+									addr = testV6Addr
+								default:
+									t.Fatal("unknown test variant")
+								}
+							case "multicast":
+								port = multicastPort
+								switch variant {
+								case "v4":
+									addr = multicastAddr
+								case "mapped":
+									addr = multicastV4MappedAddr
+								case "v6":
+									addr = multicastV6Addr
+								default:
+									t.Fatal("unknown test variant")
+								}
+							default:
+								t.Fatal("unknown test variant")
+							}
+
+							c := newDualTestContext(t, defaultMTU)
+							defer c.cleanup()
+
+							var err *tcpip.Error
+							c.ep, err = c.s.NewEndpoint(udp.ProtocolNumber, networkProtocolNumber, &c.wq)
+							if err != nil {
+								c.t.Fatalf("NewEndpoint failed: %v", err)
+							}
+
+							switch name {
+							case "v4":
+							case "v6":
+								if err := c.ep.SetSockOpt(tcpip.V6OnlyOption(1)); err != nil {
+									c.t.Fatalf("SetSockOpt failed: %v", err)
+								}
+							case "dual":
+								if err := c.ep.SetSockOpt(tcpip.V6OnlyOption(0)); err != nil {
+									c.t.Fatalf("SetSockOpt failed: %v", err)
+								}
+							default:
+								t.Fatal("unknown test variant")
+							}
+
+							const multicastTTL = 42
+							if err := c.ep.SetSockOpt(tcpip.MulticastTTLOption(multicastTTL)); err != nil {
+								c.t.Fatalf("SetSockOpt failed: %v", err)
+							}
+
+							n, err := c.ep.Write(payload, tcpip.WriteOptions{To: &tcpip.FullAddress{Addr: addr, Port: port}})
+							if err != nil {
+								c.t.Fatalf("Write failed: %v", err)
+							}
+							if n != uintptr(len(payload)) {
+								c.t.Fatalf("got c.ep.Write(...) = %d, want = %d", n, len(payload))
+							}
+
+							checkerFn := checker.IPv4
+							switch variant {
+							case "v4", "mapped":
+							case "v6":
+								checkerFn = checker.IPv6
+							default:
+								t.Fatal("unknown test variant")
+							}
+							var wantTTL uint8
+							var multicast bool
+							switch typ {
+							case "unicast":
+								multicast = false
+								switch variant {
+								case "v4", "mapped":
+									ep, err := ipv4.NewProtocol().NewEndpoint(0, "", nil, nil, nil)
+									if err != nil {
+										t.Fatal(err)
+									}
+									wantTTL = ep.DefaultTTL()
+									ep.Close()
+								case "v6":
+									ep, err := ipv6.NewProtocol().NewEndpoint(0, "", nil, nil, nil)
+									if err != nil {
+										t.Fatal(err)
+									}
+									wantTTL = ep.DefaultTTL()
+									ep.Close()
+								default:
+									t.Fatal("unknown test variant")
+								}
+							case "multicast":
+								wantTTL = multicastTTL
+								multicast = true
+							default:
+								t.Fatal("unknown test variant")
+							}
+
+							var networkProtocolNumber tcpip.NetworkProtocolNumber
+							switch variant {
+							case "v4", "mapped":
+								networkProtocolNumber = ipv4.ProtocolNumber
+							case "v6":
+								networkProtocolNumber = ipv6.ProtocolNumber
+							default:
+								t.Fatal("unknown test variant")
+							}
+
+							b := c.getPacket(networkProtocolNumber, multicast)
+							checkerFn(c.t, b,
+								checker.TTL(wantTTL),
+								checker.UDP(
+									checker.DstPort(port),
+								),
+							)
+						})
+					}
+				})
+			}
+		})
+	}
+}